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Pumps

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Professional Development Training Course for Registered Engineers

Pumps

Tape 1 Side 1 (01 track 1)

This is tape one, side one, of a course entitled Pumps. It is dedicated to professional

development training for registered engineers indicated, as I said, a three-hour course. We will

during the progress of the tape discuss the varieties of pumps that are available, breaking themdown into three sections: centrifugals, positive displacement, and specialty pumps. Ill try and

follow the discussion of the pumps with a few comments on particular applications that

hopefully will have some guidelines for uses, observation, and analysis of pump systems.

My name is Ed Hardin. I am a registered professional engineer in the State of North Carolina. I

have been practicing engineering for some 50 years and Ive had the privilege of being part ofoperating plants and the development, construction and startup of a variety of process systems,

and, of course as could be expected, as a chemical engineer in working in the conditions in the

United States today. Ive covered quite a variety of process systems and a variety of pump

applications.

The initial type of pump that well discuss is a centrifugal pump. I will discuss under this

category several different aspects of the pumps and how theyre used and how they should beconsidered for applications. Ill discuss these as values of the pumps for the various varieties,

certain concerns about their operations, and some comments, also, on the types of drivers that areused for the pumps.

First item of discussion under Centrifugal Pumps is to definitely recognize that this is a realworkhorse type piece of equipment for the chemical process industries and for industry, in

general. There are very few things around that do not require pumps in one way or another.

This, of course, even includes things like air conditioning systems where you could consider thatthe air is, in fact, pumped. We will not deal with fans and light pumping of that variety in this

particular set of tapes, but everything else from water distribution for civic situations, waste

control, transfer of materials for convenience as well as for operating use, and, of course, in-

process transfers all use pumps of a wide variety and type that well discuss.

A key unit that is regularly used in almost all industries is the centrifugal pump. It is generally

used where a fairly consistent flow is desired, where the flow is relatively large compared to a lotof other things around itsmaller flow pumps, quite often, are done with positive displacement

units. Well discuss those a little bit later. Relatively large continuous and, again, the relatively

large can cover anything from a few gallons a minute in some small situations, where maybeonly five or ten gallons might be used as a total charge or a total operating section, to systems

such as very large liquid processing plants that might have plants circulating loops that would

run 15,000 to 20,000 gallons a minute, or transfer systems from storage and other types ofcontainment areas that might go into several hundred thousand gallons a minute.


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The first item to consider under the variety of centrifugal pumps to be discussed is the open

impeller. This is the general definition of almost a basic pump that anyone thinks of as a

centrifugal pump. It has a containing volute. It has an impeller placed in it. The impeller isconnected to a shaft. There is a seal. There is an inlet and an outlet. Quite often there are a few

other things that are involved. On the impeller itself, there are some vanes that create themovement of the fluid.

This very simple pump is used for almost anything for pumping. Quite typically for water

pumping and distribution, but many hydrocarbons, gasoline-pumping applications, oil and so on

pumping applications. Its rudiments are that the eye of the impeller receives the liquid. Theturning of the impeller itself causes the liquid to acquire an acceleration, which, as the

acceleration is absorbed in the casing, is turned into a velocity at the casing edge. That velocity

is generally directed around through an enlarging cross section volute until we finally arrive atthe outlet of the pump casing. Now the liquid that came into the eye at relatively low pressure is

at somewhat higher pressure and available for transfer from the pump itself on into the process.

The pump design, the design of the impeller, the rotational rate of the impeller, the size of the

inlet, the size of the volute, the size of the outlet are all factors that come into consideration in

deciding to use this pump. The main purpose is to increase the pressure so that a liquid can be

reliably transferred from one vessel, usually at the lower pressure to a higher-pressure vessel, ora vessel located in an elevated position.

The second type is what is called the closed impeller. General characteristics of these pumps arevery similar with the one exception that in the closed impeller pump, the casting for the impeller

provides an inside and outside plate with the vanes contained between the plates. This is usuallydone in order to improve the efficiency of momentum transfer and generally used for relatively

higher-pressure situations in order to be assured that all the material that comes into the eye goes

directly to the volute and that there is relatively little circulation.

In some cases, a centrifugal pump is used with a recessed impeller. This kind of pump would be

used in places where some solids might be contained within the liquid that is being pumped. Atypical application is a waste stream of one kind or another. Very frequently used in biological

waste processing facilities in order to prevent any kinds of paper or other materials coming down

the pipeline from blocking the pump.

In all of these situations, the impeller may or may not have a leading eye ring that will help direct

the flow into the impeller and help provide a little bit of stabilization for the impeller. Of course,

on the shaft as it discharges out of the driving end of the pump casing, there will generally bebearings and a type of seal in order to be able to hold the liquid within the pump casing. The

bearings are generally beyond the seal so that the seal does hold the liquid without having them

touch or provide any possible effect on the bearings.

One of the conditions that exist because of this arrangement is that the impeller itself is

cantilevered beyond the bearings of the pump shaft. This generally requires that the bearings bea little bit heavier than one might normally expect for these conditions. Also, the alignment of


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the pump and the seal housing with the bearing housing would be something of significance.Particularly where mechanical seals are being used because you certainly do not want an

elliptical type operation of a mechanical seal. This will cause excessive wear of the seal itself

and the seal rings and will ultimately lead to a loss of the sealing involved.

This was certainly very true, also, for those pumps that used to have braided type packing thatwere installed and for any pumps that are like that today. Replacing braided packing in a pumpis a rather time consuming and tedious operation. They were very valuable and very worthwhile

methods for packing and protecting pumps in the initial situations, but, again, the alignment is

very critical and, of course, anything beyond the last support bearing on the shaft that could

affect the balance of the shaft or the balance of the impeller will be critical to the sealing, theimpeller operation, and ultimately the bearing life.

More recently a new variety of pump referred to as a disk pump has been used in manysituations. This generally consists of several plates held together with small pins, shafts or

cylindrical arrangements, near the edge of the disk where the fluid action and the acceleration is

provided strictly by viscous contact of the liquid with the disk surface. Certainly some argumentmight be made that the little cylindrical connections at the far outside edge do something to

improve the efficiency and acceleration of the liquids as they go to the outside, but these disks

are generally used in areas where minimum sheer of the liquid is a prerequisite. They generally

serve very well under these conditions.

All of the above listed pumps, whether theyre open impeller, closed impeller, recessed or disk,

can be provided in a variety of materials. Very typical for pumps are rubber linings or rubbercoatings of one kind or another. Rubber has been found to be both a corrosion resistant material

as well as a very convenient way to handle relatively abrasive slurries. The generalunderstanding is that the material itself will rather adhere or dig into the surface of the rubber

and ultimately become its own abrasion surface. Often, all of these pumps are made out of

plastic. Sometimes they are made out of graphite, sometimes fiber reinforced plastics, and, ofcourse, a whole variety of specialty metalseverything from basic steels through stainless steels,

bronzes, ferrous alloys, and, of course, into some even more exotic materials.

A key factor is there is a variety of adjustments or modifications that can be made to the pump

itself, to the casing, to the impeller, to its method of support, and to its method of sealing so that

a centrifugal pump can generally be found to be functional and effective in the majority of any

transfer applications that are around. However, one criteria that does exist there is that the betterefficiencies and better applications of the centrifugal pumps are those cases where the pump will

run relatively continuously. Starting and stopping a centrifugal pump can be, depending on the

size of the pump, a very energy intensive function so that once a pump is turned on, its long-termreliability, smooth operation, and efficiency of plant operation is best controlled by giving it a

long service factor.

A variety of sizes exist in all of these pumps. Very small centrifugal pumps, something

considered very small today, might be something with 1/4-inch inlets and 1/8-inch outlets.

Those were probably somewhat unheard of 20 or 25 years ago. Certainly some applications


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today require those kinds of operating conditions, particularly something that might be smallusage and might have to do with hydraulics.

Pump sizes go very large from there. One plant that I had the privilege of assisting in regularlyhad 1,500 horsepower, 8,000 gallon a minute pumps, and it would be very easy to list in the

neighborhood of 60 to 80 applications of that type of pump in that particular plant. I have beenmade aware that there are much larger pumps. One very interesting example that I noted a longtime ago was a pump that had an 11- or 12-foot diameter inlet that fed into a centrifugal type

pump and discharged something in the neighborhood of 130,000 to 150,000 gallons a minute,

creating a total pressure difference of something less than 20 feet. This pump was used for

removing rainwater from the City of New Orleans and there were a bank of these pumps thattransferred the water from the collection bases and collection system of the city into Lake

Pontchartrain in order to be able to keep New Orleans from being flooded.

A variety of styles exist in the centrifugal pump, too. In everything that weve discussed here so

far, weve generally looked at the idea of water coming into an inlet eye in the center of the

impeller and discharging out a side point at the terminus of the volute expansion. There are quitea few systems where the impeller can be fed not only from one inlet side, but from two inlet

sides to a center discharge and this is called a double volute system. Quite often, this was done

through a single inlet connection that is spread in the casting to allow the liquid to feed along the

shaft from either end of the impeller then move through the impeller and through a commoncentral discharge, but its not unheard for a double volute casing to have two separate inlets that

are then pumped with a variety of situations, such as a tee to split the incoming flow or allow the

incoming flow to go in both directions.

This type of pump, again, goes to the heart of the reason for using centrifugal pumps. You canget a better balance of application. You can put bearings on both ends of the shaft and improve

the alignment and stability of the pump for holding up over time. Its generally used for those

situations where consistent flows of relatively high rates of transfer are required. A very typicalapplication would be something like a cooling tower water transfer where the pump sits there

and runs on a continuous basis. It can be designed and developed for a very high efficiency and

very high reliability because of the overall balance of the system.

Another method of achieving improvements is variations on the basic centrifugal pumping

system and that is a system of multiple impellers. Quite regularly, this is done in places where

very high pressures are needed or where pumping must be done to great heights. A very typicalapplication for something like is a very deep well, down-hole pump that might have anywhere

from two to five or ten or sometimes even more impellers stacked one after the other. All

providing their own additional input to the pressure of the system because each impeller on thesystem will provide about the same pressure increase as the one before it of the given size and

the same given design. So, that if one pump might have the capability of 200 to 300 gallons a

minute with an increase of 150 to 200 feet of head, if four or five impellers were put in seriesinto the same volute casing, again, with some specialty designs, then the 200 to 300 gallons a

minute could be pumped out of a given pump with four stages at four times the 150 to 250-foot

head gain or a 600 to 800-foot head. This has very regularly been used for water recovery for


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irrigation systems, for water recovery for feeding into municipal water systems, and, of course,Im sure that many of you out there have other cases where that can be brought in also.

Of course, the other thing that we have alluded to in the discussion here is the idea of a widerange of operating rates. The one thing that is typical for a centrifugal pump is continuous

operation of a given flow rate. My leading question was that the flow should be relatively large.So, the relative concept now comes in and something for a given system that is consideredrelatively large might be down in the quarter to half a gallon a minute range because this is

something of a very, very expensive or very specialized material that needs to be added on a

continuous basis to a flowing stream. As long as it can be done at a continuous flow, the little bit

that would need to be added would be pumped regularly to a variety of applications.

Again, there are other much larger systems, as we indicated before, that could go up into

hundreds of thousands of gallons a minute. These generally might be water systems as wassuggested. However, a variety of oil pipeline systems would use very large pumps like this on a

continuous basis. Im sure that there are many places that we could follow pipelines along

through the United States and find pumping stations with, again, very large pumps like thiscontinually refreshing the pressure of the system in order to achieve transfer of everything from

gasoline products to lubricating oils and heating oils all around through the United States.

This, then in summary of the discussion of a wide range of operating rates, I tried to give you theexamples that indicate that it may not need to be a very large volume. It may be a lot of material

in relationship to the cost of the material or its potential application in a product. Therefore, a

continuous, relatively constant pressure entry and transfer rate is something of interest. Theseare the kinds of things that centrifugal pumps do very well, particularly at their output point, their

output flange.

This now brings in the discussion of several concerns that we must have about dealing with

centrifugal pumps. One of the principal concerns in working with a centrifugal pump is that itwill generally operate in either directionin the desired direction, which is the most efficient, or

it will very easily turn in the reverse direction. In the forward direction, of course, we have

pump curves that give pretty good indication of what the flow and head capacities are for thepumps. Generally these curves give you a reasonable operating range over which to work and

use the pump. Of course, a selection of the impeller and the speed of the pump gets you into a

given pressure range.

One of the things that gets very deceptive is that if an impeller is running in the reverse direction,

it quite often will generate almost exactly the same head under a no flow condition, but if the

flow is increased or requested in a large increased capacity, then the pressure available will dropoff very dramatically. This is one of the very serious situations it comes into when there are

multiple pumps in parallel pumping a given system. If for some reason one of the pumps

happens to be arranged so that it turns in the reverse direction, usually a change in wiring ofcontrols of one kind or another, often the pumps operating in the normal condition will very

rapidly run up to their capacity and then drop off in capacity. Still the system can show a

relatively decent head, but not have sufficient flow.


7/29

Of course, the other condition can occur where there may be two pumps running in parallelonein the proper direction and one in the reverse directionat startup. The pressure will be fine, but

very quickly its noted that there is no flow. The pressures drop off very dramatically and then it

comes back to the question of doing a little investigation and being sure that the pumps areturning in the right direction.

Ive included with the tapes here copies of pump curves out of several publications that indicatethe general conditions that will be affected by the pumps when operating in these ways. Of

course, an allied concern with the pump running in either direction is that they will in fact pump

in either direction. Therefore, it can sometimes be deceptive that you seem to be getting flow,

but youre not really getting it at the right pressure or volume rates and this, then, can lead tolonger diagnostic times and analyses. Quite often some other blockage is anticipated in the

linea valve malfunction. Definitely the operating direction of the pump should be one of the

first things checked when a pumping condition does not meet the expectations. Again, hopefullythe curves that are shown here give you a little better idea of the difference in performance that

you can expect under the two different conditions of operating the proper direction or in a

reverse direction.

One of the other concerns that is very significant with a centrifugal pump is the fact that we can

reach a condition at the inlet to the pump that is referred to as cavitation. This can occur for a

couple of reasons. The most typical reason is an improper NPSH sizing. Ill not go into thedetails of doing any of that right now, but net positive suction head is very important. It is

always discussed very thoroughly by pump manufacturers and representatives. Of course, there

are always indications of the required heads coming in.

The second condition that can exist is if there is some minor blockage in an inlet line. Theconditions can indicate that there should be sufficient NPSH at the pump eye, but the blockage

will tend to limit this. Under either condition, whether there is insufficient designed pump head

or there is some slight blockage in one way or another, at the eye of the impeller, we can getwhat is called cavitation. Cavitation is, in fact, the boiling of the pumped liquid due to low

pressure and then the later collapse. This boiling and collapse will cause quite a bit of vibration.

It will cause generally some significant erosion and wear at the impeller inlet because of thesevere collapse that can occur there. Generally, it will very quickly lead to the destruction of the

impeller and quite often some significant mechanical damage to the pump.

It can also lead without too much difficulty to a condition that we generally refer to as vaporbind. This is a condition where there is a status where there will occur boiling at the inlet to the

pump and it is more vapor than can be recondensed by the flow of liquid thats available or the

pump conditions that are in there. At which case, the impeller begins to spins strictly within thevapor and do very little pumping. A typical situation on that would be some blockage at the inlet

that would limit the flow, allow the boiling to occur. Another condition would be a very low

flow that will allow the mechanical energy of the pump to continue to be absorbed by the liquidin which case it would begin to boil the liquid in the pumping cavity. Under those conditions,

you see a significant drop off in the flow rate of the pump, but quite often a still rather

continuous, rather typical indication of output pressure because of the physics of the fluid


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dynamics at the tip of the impeller will still maintain the pressure in the system if there is littleflow and if there is some back pressure working on it.

Centrifugal pumps will also operate at conditions that can lead to their own destruction. Wevediscussed one of thesethats cavitation. Weve alluded to another onethats the low flow in

which case quite often the fluids are overheated and boiled. This can lead or augment cavitation,which, again, can create significant problems of temperature and pressure within the pump.Certainly one of the conditions that needs to be recognized, particularly in the low flow

condition, is any time that youre working with a pump that has any elastomeric content in the

pumping chamber itself, if the impeller is either coated or made of an elastomeric or polymeric

material, the pressure of operation will become very critical. If a very low flow occurs and avaporization of the material occurs at an increased pressure, then, of course, the temperature will

be increased. It certainly is not uncommon to find plastic or rubber pumps that have been

operated under a closed flow condition that have heated up to the melting point of the pump.The impeller then becomes one lump of elastomeric material turning on the end of a rod and it

certainly is no longer a pump and quite often can lead to damage of the internal casing of the

volute also.

These are all conditions to be avoided, of course. One of the typical ways to avoid that is to

create a bypass around the flow system so that the pump will always pump a minimum flow, or

somewhat above the very minimum flow, around to a reservoir so that the temperature of thematerial in the pump body itself does not increase rapidly if the flow drops to a very low

condition. Quite often, an orifice bypass is used for this. It will maintain the pressure. It will

maintain the minimum flow. It costs a little bit in efficiency sometimes, but its a veryworthwhile protection of the pump.

A second method that is used for this kind of operation is a flow indication downstream that will,

on reaching some minimum flow condition, open a second valve and cause a recycle into the

feed in order to maintain a minimum flow through the pump. Then, of course, a decision shouldbe made whether that is a condition to be alarmed with, whether it is something that will happen

infrequently, but regularly, and is to be recognized but need not be alarmed, or is something that

will happen relatively infrequently and is accepted when it happens, then, when conditions returnto normal, the flow conditions and so on, will return back and the bypass line will close. So,

some protections against those kinds of cavitationlow flow and heatingare always

important.

A second situation that can occur and is a matter of some concern because it will cause damage

to the pump is the high flow condition. If the downstream pressure becomes much lower than is

anticipated, depending on how motor sizing is taken care of with the pump, you can run into ahigh flow condition where the motor itself will overload and the motor or the driver of the pump

will end up being damaged in some way because of excessive load.

Quite often, pumps are requested to be designed so that they are definitely non-overloading.

This, of course, puts quite a bit of responsibility on the one with the final responsibility for

selecting the pump and driver combination. It also gets to be a matter of some concern in thebalance between pump and transfer method selection on a centrifugal pump and system design


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because often there are minor changes in system design that dont get related back to thepurchasing or acquisition phases for the pump. A small pump that is later on deemed

inconsequential from a project or the unit cost standpoint quite often will have a significant

operating responsibility or operating effect simply because it hasnt been reconsidered in theselection review of the pump. A pump that was originally anticipated to be non-overloading is

now in a condition where the system change is such that it can become a motor overloadingcondition. Of course, something that can damage the motor has multiple possible effects.Certainly one of the things that was very typical in the past would be, especially with an electric

motor, to buy it with a 1.15 service factor. This would mean that you normally had a 10 to 15%

overload capability without a particular problem.

Another thing that was often done is the specifics of the electric power supply to the pump were

arranged such that a slight overload would not cause a trip-out of the system. In that case, then,

higher amperage flow rates, particularly on an electrical motor, would give some overheating tothe pump and this could have disastrous effects in very warm climates. This is something that

might be a little bit more acceptable in a very, very cold climate where you have better

temperature protection over the windings of the motor, particularly if its an outdoorarrangement. All of these things are trade offs that are relatively bad in practice and should be

avoided. The pump and motor combination should be selected for the appropriate conditions of

operation and should be reevaluated under the conditions that are finally installed, recognizing

that periodically things change.

Having run through the variety of some of the concerns to be aware of in the centrifugal pump

selection and application, lets talk a little bit about the specifics of the types of drivers andmotors that can be used with a centrifugal pump. Several things that weve discussed already

pointedly commented on electrical motors. There are, of course, several options to be used withthe electric motors. One of the things that motor application specialists quite regularly get into

are the types of startup and shutdown conditions. Different specific types of motors can be

appropriate for these different conditions.

Generally, most people look to the idea that a pump is going to be started up with a fairly decent

pressure against it with an immediate demand for usage and, therefore, it will look to a high earlystarting type motor and running at a constant speed. Then, using a control valve if there are any

variations in flow that are anticipated or using some other kind of a distribution system

multiple orifices or specialty limited flow designed systems to transfer liquids to a multiple

application arrangement downstream. Of course, with a constant speed motor, all of these thingsare possible. It does bring in the constant requirement of a little bit of extra energy and a little bit

of extra cost for that energy and, again, depending on the size of the system that may or not be

something of concern.

With very large systems it often is. So, a second variation is often looked to and that is a motor

that can be operated at a variety of speeds. Then, using the flow indication or the flowrequirement, either the actual liquid flow rate or the desired pressure at some given point in the

line, as the basis for controlling the speed of the main driver. So, centrifugal pumps can be used

at either constant or variable speed. When they go into a variable speed situation, of course,efficiency drops off very dramatically, but you can quite regularly run into significant piping and


10/29

instrumentation and a few other savings, particularly if you are operating very close to a constantflow rate, but may only be running in the 10 to 15% flow range variation 90 to 95% of the time.

Then, a variable speed motor can be very, very effective in reducing overall responsibilities and

problems in the system by taking you down to the fact that you only have one sensing unit andone variable unit, the motor driver itself, and eliminating the questions of secondary control

loops on valves, valve operations, and, of course, the other components that come along withthat. So, variable speed drives on any motor, and certainly theyre arranged very easily now onelectric motors, are a very good way of getting good, small variation, or range adjustment of the

flow conditions.

A typical driver thats also used is an air motor. These are usually used where space limitationsare very small. Air motors, in my experience, have generally been very, very reliable and a very

functional way of doing pump driving. Usually, the cost of generating the air and the other

problems that come along with it, Id rather argue against the use of air motors for many of thecentrifugal pump applications.

Quite often the hydraulic motors are used. Again, these can be parts of overall systems wherethe hydraulic system is generated itself with a centrifugal pump, but that there are many, many

little applications somewhere down the line on the systems that need either higher pressure or

higher capability. Then, small hydraulic motors and small pumping systems driven with these

hydraulic motors can be appropriate around through multiple systems.

There are many direct mechanical drivers that can be used with centrifugal pumps. Certainly

running down through the range of things that will be familiar to us all, like gasoline engines,steam turbines, gas turbines, quite often letdown turbines that might be used for energy recovery

are all viable options for powering pumps.

Tape 1 Side 2 (01 track 1a)

This is the beginning of tape 1, side 2, of the Professional Development Course, Pumps. Weve

just been discussing mechanical drivers for pumps. Certainly one of the most interesting or

fascinating little applications of a combined mechanical drive use of a turbine for a pump is thesystem where some electricity is used from a reservoir to drive a turbine and operate a generator

during a high demand electricity portion of the day. Later in the day, the generator is then

reconfigured, rewired, or the connections to it are modified so that the generator becomes a

pump and some of the water thats been let down through the turbine is pumped back up into thereservoir so that, later on in the day when a high demand period comes again, that same water

can be let down through the system and regenerate electricity. This is a very convenient and

practical way of doing this in some of the locales that are remote from other generations, buthave the physical characters, the geologic and mountainous arrangements, to allow this kind of

collection. Of course, the attractive point would be if many of the upper level streams in the area

could be directed in there so that not all of the water would have to be pumped back up.

Other applications using turbines along pipelines might have to do with very large diesel engines

on liquid pipelines. Quite often these are in remote areas. They can be used with more of theactual pumping systems along the pipeline for thicker liquids, like oils or heavy heating oils,


11/29

where things like kerosene or gasoline are being pumped, or any lighter liquids might be goingthrough the system. Quite often, some of the large pumping units are shut down. One of the

advantages, of course, is whenever diesel is being transferred along the line, the system can be

set up so that some of the diesel can be transferred into a local operating tank and used as theenergy supply for pumps during those periods when high viscosity and heavier materials are

being pumped.

We mentioned gasoline engines as drivers for pumps. This is more typically applied from those

places that Ive seen in developing countries where its not normal to have large electricity or

convenient electricity nearby. Sometimes a direct automobile type engine is hooked up to a

pump and operated. This gives the capability of being able to bring a convenient power sourceto the pump. Again, in developed nations, such as the United States and Europe, this is relatively

unusual because of the access to electricity.

Certainly, one other application along this line that bears some discussion and, although its not a

pumping of liquids, its the natural gas distribution system of the American Southwest where gas

turbines are often used to drive the centrifugal compressors that transfer the natural gas. Again,more of the transfer and pressure increasing stations are used during periods of high demand.

When lower demand is being called for, then, of course, some of these stations can be turned off

and a little higher pressure drops are taken in certain portions of the line and still get sufficient

gas transfer. This also leaves the benefit that the gas thats being transferred along the pipeline isoften used as the gas that drives the turbines themselves. As with the diesel operated units on

large oil pipelines, these gas operated units on the gas transfer pipelines are often operated,

controlled, turned on, turned off, and the fuel supplies to them arranged by electric and radiosignal from hundreds or even thousands of miles away.

And to emphasize, one final mechanical type drive is the steam turbine. Certainly one of the

most fascinating applications that Ive been aware of with these has been particularly in the

context of sulfuric acid manufacturing process where sulfur liquid is usually pumped and burnedwith oxygen in order to create SO2, which then is catalytically absorbed and modified in a very

strongly exothermic process that generates a lot of steam in secondary heaters. This steam is

then used to drive the pumps for all of the rest of the operation, transferring the sulfuric acid,olefin, waters, and the boiler feed water into the recovery unit, to the point that the only electric

function within many of these contact plants is a backup pump on the liquid sulfur used for

startup situations. Very quickly after startup, the plant is completely self-sustaining in steam and

all operations are then done with steam turbines instead of with electric motors. Usually, theoffices might have a direct connection to a local utility for computer and certain security backup

situations, but often the acid plants are generating electricity and selling it to the local utilities.

Well, weve gone through quite a variety of conditions and things that can work with centrifugal

pumps. Hopefully, that might have given you a few ideas of other things or special things that

can be done with centrifugal pump applications that you have upcoming.

Now, lets turn to a little different type of pump, the positive displacement pump. Looking at

this, there are several significant points about them, of course. This is, in general, quite asignificant type of pump used in a lot of applications and becoming more popular because of


12/29

improvements in efficiency, I think. Particularly in the small air-operated type pumps, butwidely used in a number of applications in other ways that well talk about under specific pumps.

It does get used quite regularly in a variety of industries. Certainly throughout the specialtychemical industries now that pumps made out of specialty polymers and with the variety of

diaphragms and seals that can be put onto them are available. They are widely used in thechemical industry. Of course, theyre pretty widely used in the construction industry, too, wherethey are primarily used for reliable vacuum lift helping of water out of deep trenches and in some

other applications in waste handling activities.

There are a variety of types that exist. Of course, the typical one to start with, which is wellknown today, is the diaphragm type. Again, the general description would be two diaphragms,

usually connected on opposite sides of a chamber, with a motive force of one kind or another on

one side of the diaphragm, the pumped fluid on the other side, and a method for being able tomove the diaphragm by force on one side causing an expelling of the pumping medium on the

non-pumping side. Once a limit is reached on pumping, then a shift in the operation of the

valving is made so that the pumping begins in another direction. So, usually, there are twochambers and its a bi-modal type pumping operation.

Another type of positive displacement pump that is not usually possibly identified under that

way, but is truly one that uses a flexible impeller, is an impeller that has rubber ears orprotrusions on a rod. The rod is then eccentrically mounted in a pumping chamber and the little

impellers, as they move around, spring out, remove liquids, and as they get forced into the pinch

on the eccentricity arrangement, it will move materials forward.

Certainly intermeshing impellers are also used in positive displacement type pumps. Every nowand then, youll run into impellers mounted and working with a cage. The cage turns with the

impeller and becomes a method of controlling when the volume is in the pump and when the

volume is moved through the pump. Often, that is also used.

Gear pumps are very, very similar to the intermeshing impeller type pumps. Usually, they are

used at relatively high pressures or in situations where very accurate flows are required. Ofcourse, sometimes the reverse of that is also used at a gear pump every now and then or a gear

arrangement is used as a measurement of flow. Thats not within the purview of what were

going through here, but sometimes it can be used in that way, too.

Of course, the pumps can be made out of a variety of plastics. They can also be made of all the

varieties of metals and the combinations of seal types and shaft and bearing mounting types, all

work in this, also. Many, many of the impeller, impeller and cage, and gear type pumps will usebearings mounted on both sides of the pumping chamber. This gives a great stability to the

pump and allows closer clearances to be used. This is one of the things that improves the

efficiency and increases the possibility of using this for higher-pressure applications. Withplastic pumps, of course, you are going to be limited to the strength of the material of which the

casing is made, but often theyre used in the same way with seals near the bearings so that those

shafts are held very positively.


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One of the older types of positive displacement pumps that has been around for a long time andused in many, many applications, is a piston type pump where very large pistons are moved back

and forth. This, of course, is the classic reciprocating steam pump that is most typically found in

discussions of old mining operations where a large pump like this was used to move water up outof the lower depths of the mines. Some of the very old discussions talk about using one pump on

one level and having it work through three or four different mine levels, sequentially movingliquids from a lower level to an intermediate tank and then from that intermediate tank to anothertank and another tank and so on, until they finally get it up above ground or out of the mine and

are able to discharge it. Of course, the reasons for this generally came to the idea of the pressure

capacities of the piping in the systems that were available. So, they did have to work with no

more than a 30, 40 or 50 psi differential. Of course, the old problem of the bugaboo of amaximum 12 or 13 psi suction lift is usually available with the very cold waters that were down

in the mines. If they were using it for suction lift, then, of course, that was part of the differential

question, also.

Another positive displacement type pump that is often realized is one that is a combination of a

piston and a diaphragm. Instead of using a motive fluid directly on one side of a pump, amechanical piston is moved back and forth. The inelasticity or the incompressibility of a

pumping fluid is then utilized to cause the diaphragm to move by the action of the piston behind

the diaphragm and in a motive fluid. Then, on the other side of the diaphragm, a fluid can be

pumped. This type of pump has the advantage of some very high accuracies. There have beenmany variations on this pump that have been developed with changeable linkages so that a

variety of pumping rates can be achieved with a given pump and usually with a very wide range.

Some of these pumps are adjustable in run so they can actually be a very closely controlled and

automatically controlled during the operation of the pump. They have many applications inrecirculating transfer systems that require a basic concentration that can be measured. For

instance, one of the areas very regularly used on this is in cooling towers for various treatment

chemicals to go into the water where the conditions of the water are measured on a regular basisby instrumentation. The adjustment is made in run in order to be able to keep specialized

conditions and be sure that there is no bacterial growth within the cooling tower waters. Also,

any other treatment requirements for the water are maintained.

Special metals we mentioned before can be used for all of these pumps. Plastics can be used for

them. The development and requirements of the springs that are often used on the inlet and

discharge of the diaphragm sides of positive displacement pumps, also the seal surfaces and theball seals that might be used on these diaphragms, all become matters of some significant

concern to be assured that youre getting the pumping action that you want, as well as the pump

life that youd like to have and not having them eaten up or destroyed by the materials passingthrough them.

Generally, with the diaphragm pumps, there is not much of a concern with very high pressures.The operating fluids that supply them sometimes run into conditions where people will actually

use these pumps in what is referred to as a dead-headed condition, or a closed discharge

condition. As long as the driving fluid is relatively low in pressure, that can generally becontrolled within reason. So, these pumps can be used for filling and discharging operations


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where a manual valve or a full-close, full-open valve system is used and the pump, underavailable driving fluid conditions, will pick up and begin its transfer as soon as a valve is open.

However, some of the other type pumps, particularly the gear type or the eccentric impellertypes, generally have within them an internal relief valve to prevent over compression of a

relatively incompressible material in the pump and to prevent destruction of downstream pipingsystems. Sometimes these reliefs discharge immediately back into the suction side of the pump.In those cases, some very serious consideration must be given to the amount of temperature

pickup that might occur because, again, you can run into a condition of vaporizing the fluid in

the pumping chamber because of the mechanical action of the pump. On occasions, these relief

valves will discharge back into the supply vessel to the pump. This is a much-preferredarrangement because it does protect the pump and the people around it so that there are no

physical destructions of the pieces of equipment.

These pumps are available in size varieties that range from pistons that might be millimeters in

diameter and have strokes millimeters long, in order to provide very accurate low flow

discharges of materials for blending purposes, and can go up to situations where, in one plantwhere I operated, we were normally pumping a 40% solid slurry at 1,200 to 1,300 gallons per

minute and increasing the pressure up to 600 and 800 psi in one stage on a steam powered piston

type pump. Generally, the varieties that fit into these pumps, of course, fall into the categories

that we all generally see and recognize, and thats capacities of 30, 50, 100, 200, 250 gallons aminute.

The mechanical type impeller pumps and gear pumps, as they start getting into the 50, 75, and100 gallon a minute range, generally start getting expensive fairly quickly because of

requirements of gear reducers, additional protection, and the casing size and strength designs.So, be prepared if youre looking for that type of pump. Youre going to see some very

significant prices on them as the pumping rate goes up.

A variety of style is also available in these pumps. There are many pumps that operate as single

situations. There have been series of pumps that were used in many specialty applications where

there were multiple stages within a given pump that were used to provide small pressureincreases and a little bit more accuracy in its normal functioning operation. This was usually

done with four different check valves instead of possibly two on a diaphragm or piston

arrangement. Some changes in pressure were adjusted in that way.

In terms of multiple inlets, certainly this is not something that you look to as you get a double

volute pump with a centrifugal, you dont realize the same kind of condition with a positive

displacement pump. The closest comparison might be a double diaphragm pump that operatesrelatively continuously and would have one incoming line that then feeds into two pumping

chambers. One being used for pumping, while the other one is going through its filling cycle and

the expelling of the transfer pumping fluid. So, the bi-modal operation could be considered to bea double volute, but its quite different.

Sometimes, of course, with the gear type systems, there could be multiple impeller arrangements.Again, very high-pressure situations might require something like this. There are cases where


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these pumps are ganged together in order to achieve higher pressures. This is a very delicatebalance situation and something that should be reviewed rather thoroughly with the

manufacturers any time it is approached.

Another thing thats quite typical with several different types of the positive displacement pumps

is to find arrangements of a variety of pumping size modules that can be created on a singleshaft. So, that at a given turn, a specific amount, that would be different for different fluids,would be discharged per rotation. This is used in order to provide a mixed material of feeding

into process operations. Quite regularly this is used in some water treatment situations. Ive

seen it used with ratchet type drives that do create a single feed rate at a given time and do it as a

shot. Ive seen other situations where these are actually mounted on the shaft of a pump, or amotor, I should say. Then, each turn of the motor creates a certain transfer of different quantities

of fluids on a continuous basis.

The operating rates of these systems can vary in a variety of ways, but the applications are

usually highly specialized. Again, those who work in the industry will be able to help guide and

review with you anytime that might be something that would be of interest to you. In anyoperation that you would have and, of course, in these situations, quite often there are

arrangements where individual chambers within the system can be slightly adjusted in order to

keep a certain criteria of downstream mix conditions, even though some of the materials might

change a little bit in consistency or conditions.

One of the rather unique applications of pumping systems such as this, where the old lubricators

that were used quite regularly on large pieces of equipment that had many places where just alittle bit of oil or lubrication was required, you would see banks of these with each little

discharge point visible under a glass cover, or a transparent cover of one kind or another,dropping each individual drop of a lubricant so that you could check and make sure that every

point was being lubricated in a regular method. Of course, sometimes there were some operating

surfaces that needed a little bit more lubrication than others. So, we started working towardputting different size pumps in different points down those lines.

Having reviewed, again, the variety of types and some of the conditions under which theyoperate, its now appropriate to look at the concerns and special problems that may occur with

positive displacement pumps. To go down the line in a similar pattern as we did on the

centrifugal pumps, one of the concerns is the idea of whether the pump will run in either

direction. Generally they will not. Quite often, if operated in a reverse direction, something willvery definitely be obvious that something is going wrong. Typically, there may be check valve

situations around the pump that will chatter or make specific noises to indicate something is

difficult there. So, checking out rotation prior to hook up is very important with positivedisplacement pumps. That should certainly always be very carefully done at initial startups,

either in original applications and installations or after maintenance work.

Beyond the idea of whether they will run or just mechanically operate in either direction, there is

the question that since it is a positive displacement pump, if in some way the system is set up so

that it is pumping, or trying to pump in the reverse method, it will definitely not do the thing thatyoure looking for it to do with transfer of material in a given direction. A very dangerous


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situation of the reverse may occur and a material quite possibly may come back through thepump that is much more dangerous than the material that you are trying to pump. Therefore, the

conditions of operation are significantly changed and this, too, is an item that needs to be very

carefully considered and reviewed as they will begin operation.

The pump will very definitely cavitate. There are conditions, particularly suction starveconditions, where very disastrous things can occur. A positive displacement pump will verydefinitely continue drawing on a closed container and, quite regularly, some of those containers

have been drawn in if they are not appropriately vented or provided with the sufficient strength

for low-pressure operations. I think many of us have seen that as a problem, periodically, even

with using centrifugal pumps on pumping out storage tanks. Its not a very attractive situation tofind yourself in. Generally, its not a particular disaster, but in the case of a positive

displacement pump, it could be and it could be more serious than in most other situations

because of the strength of the tendency to operate and to create fluid transfer.

We mentioned earlier the idea of being careful about relief of the pumps and keeping them under

the proper conditions. These problems of vapor binding or boiling of a material inside a positivedisplacement pump, particularly the gear type or the rotary type, is something that is also of

significant concern. Generally, one of the things that we might consider in using these pumps is

that they are often pumping a relatively viscous material, which might generally indicate

something that is thicker or higher in possibly organic content. At least, in my generalexperience, a lot of it has been organic material. Of course, once you start getting too hot there,

then you will be creating dried materials and carbons and some very serious destruction and

problems can occur if you try and run under those conditions.

The pump will very definitely operate at conditions that can destroy itself. We have indicated acouple of those, cavitation and low flow conditions, definitely overheating. Weve just reviewed

that one. High flow conditions. Certainly things like that can occur, too. If the sizing of the

pump, the sizing of the system, is not carefully done and the downstream pressure happens todrop in any of a variety of conditions, you may find yourself in a very high flow condition due to

efficiencies or particularly a new pump or new impeller situation that can, again, get into motor

overload conditions or, worse than that, overloading the downstream transfer system in variousways that can cause significant damage to that.

Definitely with a positive displacement pump, blocked flow conditions are something to be very

carefully reviewed. System drainage, to be sure that material and liquids are out of the systemand cannot set up once a flow system is shut down, is a matter of significance with positive

displacement pumps. It is very inconvenient to have to take down a pumping system in order to

be able to remove a catalyzed plastic or a very hot plastic that has been allowed to cool and setup. All of these things have happened in industry. They are certainly not desirable. Thats one

of the reasons why I mention them here because they could be of significant concern for you to

pay to attention to and consider as you begin putting systems together with positive displacementpumps. The control of the temperature, the control of the materials in there, and particularly the

removal of the materials in there, can be very important for the overall safety of the plant and

personnel as a primary condition. Of course, it can be very detrimental if improperly handled tothe physical aspects of the motors and the pumps themselves.


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The final item is a general requirement on the positive displacement pumps or, again, the variety

of drivers. Weve mentioned that fluids can be used with the diaphragm type pumps, either air

or liquids, to be able to move the diaphragms. This can be done in a variety of ways. It can besupplied from another pump, it can be supplied, of course, from air compressors, but periodically

these type pumps are driven with electric motors. Again, you have the operation decision ofwhether its a constant speed motor or whether you need a variable speed motor and all of theattendant requirements of making the decision of which is the appropriate drive to use.

Air motors are less often used for positive displacement pumps. They certainly can be used if

conditions warrant. Usually, an air, rotating motor is not significant, but certainly lots and lots ofair-operated double diaphragm pumps are used for transfer of materials.

Hydraulic motors certainly could be used. Now, we then run into all the questions of the othermechanical type drives, whether they be gasoline engine, steam turbines, gas turbines, and so on.

There might be applications for using these, but, in most situations on positive displacement

pumps, I think youll find that theyll either be air operated or electrically driven. If there arespecialty requirements of using other driving types, then there will be specialty industrial

conditions that will dictate this. Thats something, again, that should be very carefully reviewed

with the vendors, makers of the equipment, and applications people who are considering putting

them in. The special requirements of the drive type and drive conditions, the powered materials,and instrumentation that goes with it, are all things that should be very carefully discussed before

making a selection of specialty drives for positive displacement pumps.

As a little diversion at this point, I would throw in a consideration that has always been a bit of a

fascination to me and thats to look back at steam engines as they operated and recognized thespecific requirements for water transfer that existed in the old steam locomotives. To recognize

how peculiar and unusual the conditions were of a very large moving mass of equipment that had

to be regularly provided with a consistent and reliable flow of fairly good quality water in orderto create the steam necessary to make the engine drive as it rolled down the tracks. The old

conditions along the tracks of recognizing the water tanks and the refilling of the water tanks

and, of course, to look at many of the things that are seen around these days, particularly incentral Europe, and in pictures that Ive seen, anyway, of areas in China, Mongolia, and Eastern

Russia, of engines with large cooling plates on the discharge of the steam operating cylinders so

that the discharged steam after its used is condensed and recycled in order to be able to limit the

number of water stops that had to be made. I have to tip my hat and throw a little word ofsignificant praise to the gentlemen of long ago who came up with the techniques of being able to

keep all of these systems going and operating on a reliable method on that massive hunk of

material hurdling down a set of rails. I hope that this little diversion has been of interest to you,but we have now come to the end of tape one, side two of the Professional Development Course,

Pumps.

Tape 2 Side 1 (01 track 1b)


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This is the beginning of tape 2, side 1, of the Professional Development Course entitled Pumps.In this portion of the tape, well begin talking about some pumps that are a little less common,

but still widely used in many specialty-pumping applications. Ill refer to them generally as

progressive cavity pumps. There are other references that are used in many magazines of screwtype pumps or peristaltic pumps. Sometimes these are a little bit more specialized applications,

but generally, as I said, Ill begin the reference as a progressive cavity pump.

The operation of this type pump is fairly easy to describe, but not very easily defined because of

the variety of pumps that are used in this application. Generally, the movement of one rotating

unit of one kind or another inside the cavity creates a passage that is moved forward during the

operation of the pump and provides a discharge. Now, obviously there is an anomaly in thisimmediately because of the new peristaltic hose type pumps that have been referred to where

there is an external mover that, indeed, forces the liquid along down through the pump. So, the

general application is that there is a portion of material to be pumped that is, in some way,isolated in a chamber. Then, by the action of some mechanical means, that unit of pumped

material is moved along through the system until it is discharged, again, in another location at a

higher pressure and so on.

Generally, these pumps have somewhat specialized applications. They can be used in a wide

variety of situations, but because of cost, applications, areas, space, and other requirements, they

are often used as a final resort pump. I hesitate to use the item, last resort, but it generallyrequires unusual conditions that are not normal conditions to consider using this type pump. One

of the areas of application that are very typical of these pumps are non-newtonian activities. Of

course, this now covers quite a range of fluids and can include everything from slurries to verythick materials, to materials that have very specialized sheer characteristics where you would like

to have very low sheer conditions when youre actually doing the fluid handling on a mechanicalbasis, but a more moderate sheer as the flow gets started in order to take advantage of certain

characteristics of sheer viscosity that can occur.

Here, I would interject a little comment that I remember from physical chemistry education from

quite a while ago. Our professor said that one of the things quite regularly done with new people

going into the study of physical chemistry was for those more experienced to be in there andbegin talking with them and telling them about physical chemistry while playing with a little ball

of material in their hands. Then, just toss the ball to the newcomer and watch the reaction. The

little ball would be a material made out of a cornstarch-water mixture that, as long as it was

kneaded and rolled and worked and kept in a relatively high sheer condition, would remain as asomewhat plastic type or rubbery kind of ball. It could even be bounced and tossed around for

people to move, but if it wasnt worked on a continuous basis, it would turn into a fluid. It

would just be a mess all over the persons hands. So, this is one of the conditions that can existwithin these pumps, too. There are materials that will react in this way and so the sheer

conditions in the pump and the mixing condition in there have a big effect on what happens with

the performance of the material in the pump and the material after the pump.

Going down through the variety of types that we can run into with this type pump, one of the

very simplest is a screw pump. This essentially is like intermeshing threads on a screw. For me,one of the simplest comparisons that I might offer is somewhat like a twin screw extruder, but


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quite often the screws are intermeshing rather than tangential and so they might be thought ofmore like a lobe air blower that is used as, again, a progressive cavity type pump, but used for

air. Screw pumps are used for very thick liquid materials or liquid-like materials and one of the

specific applications that Im aware of using this kind of pump is pumping very thick slurriesthat are used to create catalyst-based materials and pump them through a dye as a paste-like

material. Then create the size that youre looking for as the catalyst support or the catalystmechanism.

A variety of screw type pump might be called the mated impeller and lining pump. Of course,

there are trade names that go with these things and several people making them now. One of the

widely known makers of this type pump in the past has been Moyno. I do not suggest that this isthe best of those available, but it is one of the names and, unfortunately, it has often been used as

a characteristics reference to this type pump. However, there are alternate manufacturers of this

same type pump. In this case, a screw-like unit is turned within a sinusoidal type lining.

The several specific requirements that come into using this type pump are that the drive usually

must be flexible since the pump, in fact, turns in a generally eccentric type motion as it worksinside the lining material. Also, one of the things that becomes a bit of a question on this is the

sealing around the shaft as it begins to drive. This has been an area of some interest and concern

over time with the materials. However, certainly one of the things that is very true with this

pump is, that in use, particularly in non-newtonian fluid applications, it can be very valuablebecause it does have limited sheer characteristics. So, you can handle material in a very gentle

way through this pump and through the rest of the piping system. So, it is usually very reliable

for those situations.

Finally, weve made a couple of allusions in the general discussion, but the peristaltic, or hose-type pump, has been a relatively recent innovation in the last 10 or 15 years. It has certainly

been, Im sure, a lifesaver for some people in some applications. The general condition here is

that a hose is laid in an arch of some kind and a driver has connected to it several arms. At theend of those arms there are rollers. As the roller comes around and approaches and touches the

hose, it creates a backflow block. Then, by rolling down the hose, moves material down through

the hose and forward. A very simple idea. Something that started out as possibly a laboratorycuriosity, but functional, has now become an industrial pump in many applications and certainly

very serviceable for many materials.

I do have some concerns about applications of these type pumps because of the potential for tubefailure. One of the questions that always has to be balanced out in any plant design is the

question of a little bit of leakage on a continuous basis versus a very large leakage on a failure

basis in other ways. Certainly, working with smaller pumps or different pumps with long knownshaft seals, you cannot completely eliminate all leakage all of the time. So, for some materials,

thats something that would want to be avoided and, certainly, this hose type pump is a way to

consider avoiding that. However, then youre faced with the question of what is the real hoselife in the pump because if the material is as dangerous as implied by the desire to completely get

away from a seal question on a pump, then if the hose were to fail in operation, the loss would

probably be even greater and more significant at any given time. So, the hose failure nowbecomes a factor and we get into the cost trade-off of how frequently do we change out the hose


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in order to minimize the potential for failure versus the cost of maintaining control over aleakage near a shaft on another variety of pump.

Certainly, all of these pumps that weve suggested here, the screw, the mated impeller and lining,and the peristaltic type pump, can be made with a variety of materials. Quite frequently, the

liners are rubber or very flexible plastics. Often, specialty metals are used in many of thesepump systems. Plastics are quite regularly used, particularly for the mated impeller and lining.These become very specialized plastics due to the wear conditions that can occur, particularly if

you are pumping slurry with a material that has any wearing characteristics to it. Of course, the

rubbing aspect of the impeller or screw inside the mated lining will offer a question of

contamination of material being pumped. So, thats something that has to be taken into accountwhen considering this.

From the metal standpoint, certainly with the screw type pump if theyre intermeshing, there is awear and clearance question that will always be there. With any of the other type pumps,

particularly the peristaltic or hose type pump, the big questions there are what are the

surroundings made out of and what do you want to make the support and the rotor arms, and soon, so that is not the principal point of failure of the system.

Sizes of these pumps, of course, are available in quite a range. Many of the mated impeller and

lining pumps have a limitation on lower end size, but they can become very large. Other pumps,the screw pumps certainly, would generally be moderate in size. Ive never experienced the

application of these down in the fractional volume flows or the milliliter per second type flows,

but certainly in larger flows, things that were frequently faced with the 30 and 50 gallon a minutescrew type pumps have been used very regularly in those.

As for size variety in the peristaltic or hose type pumps, many vendors will bring those out and

discuss those quite regularly with you. They can be very large. Ive seen advertisements for

them with six- and eight-inch diameter hoses, which means a pretty significant drive and somepretty significant space requirements, but for many applications, this is something that is worth

considering.

With these pumps, also, there are a few things that can be done in terms of installation style.

When I speak of this, Im thinking more of which end is fed, whether its fed from the powered

end or from the non-powered end. Particularly with the mated impeller and lining situation, this

can be done very easily, so you do have a variety of opportunities there to select placement andthe arrangement of the motor and pump situation. Certainly, if you are driving it from the

discharge end, youre now into the point that you have a pressure concern for the material as it

comes to the discharge. So, your sealing is going to be a little bit different. Something like thismight be appropriate in a place where the pump is used to create a mix as it comes down the line

and that you really dont want to have the sealing problem where there might be a combination

of solids and liquids that would not possibly exist at the end of the mixing use of the pump.

With these pumps, system arrangements can be rather interesting. It is not unusual for some of

these situations to see series pumps because of pressure or mixing requirements, but, of course,parallel pumping systems on all of these are possible. Again, the usual recommendation is to be


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sure that your relative sizes, flows, and so on, match so that one pump is not fighting another ifthey are installed in parallel.

Generally, each size of these pumps is relatively limited in its operating range of rate. A givensize only has a certain speed range within which it can operate. So, you are much more affected

by rate and in selection of the unit that you want to use than you might be with some otherpumps. Centrifugal pumps can give a very wide range of operating flow rates even to thestandpoint of changing impeller diameters in order to effect or allow combinations of flow and

pressure that were considerably different from what a pump might have originally been selected

for. With these type systems, theyre a little bit more mechanically limited in what they can put

through the operating components of the pumps themselves.

Having gone through a general discussion of these type pumps, I would at this point offer to you

a suggestion that a very good reference to be able to see the variety of internals of a number ofpumps to consider something like this, and several other varieties as they come along, would be a

specialty handbook that was published by Power Engineering magazine in October of 1954.

That may sound like something quite old and possibly outdated, but I think youll find that its anexcellent reference and a very convenient thing. I would suggest that the publishers of that

magazine be contacted. You may be able to find examples of that little handbook still available.

Of course, manufacturers of pumps generally put out small magazines or handbooks on pumpdesign and varieties. All of these are excellent references to have, but the systems put together

and shown by trade magazines will usually give you a very broad cross-section of the types of

pumps that are available on the market and give you a little better chance to see what all isavailable. Of course, the old standard reference of the Perrys Chemical Engineers Handbook

also includes demonstrations of quite a few pumps. This is a worthwhile thing to have availablewhen youre considering any of these things, too. Some of the pictures and illustrations that are

shown can certainly help in understanding whether the pump will indeed fit to your application

and making an investment in something like this. Usually, its somewhat more expensive thanthe more typical pumps and, therefore, as you make that investment, youll want to go through

the range of information available and have a good understanding of what you want to do with

the pump as you move forward.

With these pumps, of course, certainly there are some concerns that have to be addressed and

weve discussed this kind of item on the reviews of the centrifugal and positive displacement

pumps. Certainly, lets run down through the general categories here, too.

Because of the special mechanical requirements of these pumps, generally they will not work in

either direction. You can have some safety in that, but, of course, that brings back the commentthat we mentioned on positive displacement that it makes the requirement of checking the

rotation before final use and hookup much more important. Generally, these pumps will not

really work in either direction. By that I mean the transferring flow. Certainly, on things like theperistaltic or hose pump, if the rotation were reversed, you would end up having some backflow

possibilities, but youre very limited because the downstream piping arrangements usually dont

give you a supply. So, you would often end up being in a starved condition, which may not beappropriate for the materials or construction of the selection that youve made.


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Screw pumps, particularly the mated metal units, quite possibly might be able to turn in a reverse

direction, but the gearing and so on inside those generally makes that an unpopular thing to do

with the manufacturers. Youll generally find in their literature very strong recommendations,again, to be sure of the rotational direction because the pump is designed to work in a given

direction. Reverse directions certainly could cause some serious internal concerns.

These pumps are usually not moving at high rates of flow and, therefore, there is less concern

about the problem of cavitation. Now, that does not mean that boiling cannot occur in these

because, certainly, youll recognize that if a downstream line is partially plugged and you have

this essentially positive displacement pump, you could put an awful lot of mechanical work intosome liquid very quickly. If there is the possibility of some fluid slip or some recycling inside

the system, you can very easily get into boiling conditions and possibly the cooling and collapse

that are the creators of the problems of cavitation.

Generally, because they are specialized application pumps, their arrangements are such that

people are pretty sure that they dont allow them to get into those conditions. So, the cavitationand the vapor binding questions go down in basic concern, but are all there in overall concern to

be sure that those conditions are avoided. Of course, operating manuals for the pumps

themselves and, hopefully, the representatives of the specific pump manufacturers, if you move

into those, would help and review with you any of the arrangements to offer their suggestions tobe sure that those kinds of conditions will not exist.

A very big concern, though, is that because they are very mechanical in nature, there are somevery serious concerns about use of these in operation. If the feed to the pump is in any way

arranged so that something that is larger than the cavity will drop into the pump, its very easy tojam one of these systems or create a significant piece of damage to the internals of one of these

systems. So, some kind of assurance of small particles feeding into any of these pumps is a

matter of some interest.

Certainly the conditions of low flow, many of these positive displacement pumps and these are

representatives of that will indeed get into an overheating situation. Series of high flow isusually very difficult to obtain, but variations in viscosity, density, or downstream conditions can

easily create conditions that would lead to concern to motor overheating and overloading, or

drive overloading in terms of what is there.

Of course, finally, speed is something to be of great interest. Speed, of course, is a significant

factor in friction, particularly with flow rate or, in any case, the material might be somewhat

limited in flow. If there is friction, then internal damage can occur. We suggested that in thecentrifugal pumps where we mentioned that using a plastic pump and pumping a boilable liquid

against a relatively high head could create a condition that is so hot that the impeller softens up

and is destroyed. The same thing can occur in many of these pumps if youre trying to pump amaterial that is either too hot or youre trying to pump it at conditions where the friction inside

the pump itself can increase to a point where the internals can be damaged. You can run into

some very serious problems on replacement and rebuilding of this type pump. They are a veryexpensive base unit and replacements and modifications are comparably expensive.


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The last item that weve generally discussed in looking at the variety of pumps, as weve talked

through them, are the drivers. This is one of the areas where the progressive cavity pumps

probably offer some very interesting alternatives, mainly from the standpoint of use in varietiesof flow rate conditions. The general aspects of drivers for these are very similar to any other

pump and, certainly, electric motors are the most typical drive for these. Probably less potentialfor application for any of the specialty situations, like turbines, letdown turbines, or gasolineengines, and so on, simply because of the complexity of the mechanical system for being able to

connect to the pump and to drive it.

The electric motors, particularly variable speed electric motors, would offer quite a variety ofopportunities with these pumps. I would review for just a minute one particular application that I

was exposed to. We had a relatively thick paste that was to be conveyed through a relatively

long pipeline. General calculations on the flow conditions in the pipeline indicated that thepressure drop was so severe that we would probably have to go to thick wall piping on the

system. However, in reviewing and looking at the flow rates, it was very easily understood that

the designed flow rates were fairly high and that, because of this, the pressure drop wascorrespondingly high and that, under general pumping conditions, we would probably be in

somewhat better or more favorable conditions. So, the system was put together with a relief

valve, basically a rupture disk in this case, at the feed end of the system to be able to protect the

piping system from high pressure. The pump itself was then arranged with a variable speeddrive and the material was started at low flow rates, moved up to a moderate flow rate very

quickly in order to get the line into a full condition, and then very quickly controlled to the

desired operating flows by carefully watching the line pressure. Certainly, we generally operatedfairly close, again, those are all relative terms, but at something in the 80 to 85% of the designed

operating capabilities of the pipeline that we were using and had very successful service. It was5 to 8% below the typical design rate that might have been used for that pipeline, but given those

situations and the maximums that could occur with the pump, the relief mechanism was a

completely satisfactory protection for everything involved and worked out very nicely for theoverall system.

Certainly, this kind of arrangement is possible in any of the other pumps that are there, too.Again, operating rates are, as I suggested earlier, generally of more concern in selecting these

pumps. So, your variations are more limited than under some other conditions. Certainly for

some systems, air motors or hydraulic motors might be appropriate for these units under very

specialized arrangements, but, as I said earlier, the very mechanical type drives of very largeengines, steam and so on, probably are inappropriate to these much more mechanically involved

pumping systems.

Weve now spent some time reviewing each of the several types of pumps and discussing some

of the characteristics about their application. Now, I would like to add to this section that Ill

refer to as a kind of pump magic. This is something to be aware of and, hopefully, the littlesuggestions and guidelines in here will be of some help to you as you look at pumping systems in

the future.


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The first one I would like to review with you is the idea of casing pressure distribution. Thisapplies primarily to centrifugal pumps, but it was a very interesting thing for me to learn some

time ago and I think that its important enough to pass it on as a special idea. That would be the

understanding that if you look at the volute of a centrifugal pump casing, you see that thedischarge from the impeller is isolated from the inlet as it comes in by the action of the impeller.

The spinning of the impeller creates the head that is recognized or measured and realized in theoutside edge of the volute. That feeds out through the discharge of the pump. The impeller eyeis, of course, on one end of that impeller, or one side of the impeller, and on the other side of the

impeller is the drive shaft. Therefore, the liquid connection behind the impeller is a direct

involvement of the pressure in the casing volute. It is held there by the action of the pump and

by the action of the impeller and isolated in the back of the case so that the whole back or driveside of the impeller case receives essentially the same pressure as the pump discharge. This

means that the seal on the pump shaft sees, on a continuous basis, the highest pressure in the

pump. On the inlet side, or the eye side, there is, of course, some leakage flow back downbetween the impeller and the casing, also, but its going down to the lower pressure of the inlet

flow. Thats one of the inefficiencies in the pump, but the shaft side regularly sees the pressure

of the discharge of the pump. So, thats one of the things to keep in mind as you select and pickyour pump pressures and your pump sealing. Thats what will occur.

There is a way to resolve that problem, though. If the pressure at the casing, or at the seal for the

system, seems excessively high, a very simple solution to this is to go into the impeller itself anddrill a hole from the back of the impeller, the solid plate, through to the eye and very close to the

shaft. This will provide enough leakage so that the actual pressure seen at the shaft will now

come closer to the inlet pressure rather than the outlet pressure and the potential problems forsealing are somewhat reduced. Im sure that youll find that there are a variety of pumps

available on the market that will provide you with impellers that have just such a hole, low andclose to the shaft, and in the back section of the impeller plate, to provide just this kind of

protection.

It is, of course, particularly attractive to look at places where something other than a mechanical

seal is used. Particularly things like packing and reducing the pressure that must be recognized

by that first roll of packing will improve packing life and reduce packing difficulties for anypumps that might happen to still use that. Of course, its a very easy way to reach that. The

other thing is the actions of the seals themselves maintain those conditions. Also, recognizing

that if there are just even slight solids impurities in the flowing stream and they are under very

high pressures in the back, they can be forced out through the seals. If theyre a wearing typematerial, they can, of course, have a very serious effect on the surface life, or the seal surface

life, and thats an undesirable. Of course, the other thing is if you are flushing the seals with a

water of some kind to try and prevent liquid from moving back toward the seal, by lowering thepressure that youre pumping against, youll generally have better control over the amount of

flush water that goes inor whatever the flush fluid might be. You will be protecting the seals

to an even greater extent because of the reduced pressure downstream and the circulation of thepumped liquid back to the inlet, giving you a little bit more assurance that, in the immediate area

of the seal itself, any flush liquid that goes in there would be more favorably positioned under

general circumstances.


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As were very close to the end of tape two, side one, tape situation, I will discontinue activitieson the discussions of these other special points now and resume again on tape two, side two.

Tape 2 Side 2 (02 track 2b)

General Characteristics of Pumps

Pump Magic

The second item that Ill discuss and review with you for a moment is the idea of seal andpacking pressure options. The first item that we talked about was one way of controlling seal

and packing pressure. However, there are other ways to do this. Somewhat unusual, but not

necessarily infrequent, is to actually arrange the inlet of the liquid to come in on the drive shaftside of the impeller. This way, youre always sealing against the incoming liquid conditions.

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