Hydraulics-final na as in

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INTRODUCTION

Hydraulics is a topic in applied science and engineering dealing with the mechanical

properties ofliquids. Fluid mechanics provides the theoretical foundation for hydraulics,

which focuses on the engineering uses of fluid properties. In fluid power, hydraulics is used

for the generation, control, and transmission of power by the use ofpressurized liquids.Hydraulic topics range through most science and engineering disciplines, and cover concept

such as pipe flow, dam design, fluidics and fluid control circuitry, pumps, turbines,

hydropower, computational fluid dynamics, flow measurement, river channel behavior and

erosion.

The word "hydraulics" originates from the Greek word hydraulikos which in turn

originates from hydraulos meaning water organ which in turn comes from hydor, Greek

forwaterand aulos, meaning pipe).

Hydraulic power converts the energy from pressurized fluid into force and motion.

For this reason it is often also referred to as fluid power. Compressed air or pneumatics and

steam are also considered part of fluid power as air and steam are considered fluids in the

sense that they flow under pressure and can be utilized to produce force and motion. The

advantage of hydraulic power is that hydraulic fluid is virtually incompressible, that is, it does

not change volume when under pressure. This important characteristic is well used in

hydraulic machinery to hold loads in position, to produce smooth continuous motion even

under changing loads, and for safety systems.

It was then that French philosopher Blaise Pascal discovered that liquids cannot be

compressed. He discovered a law which states: Pressure applied on a confined fluid is

transmitted in all directions with equal force on equal areas. Pascal formulated the law in the

17th century - pressure exerted in a fluid acts equally in all directions. The apparatus is two

vertical cylinders joined together with a fluid inside. The fluid moves freely from one cylinder

to the other. The cylinders are unequal - one has an area of 1 sq.in. and the other 5 sq.in..

Pistons are placed in the cylinders and with 500lb on the larger and 100lb on the smaller

there is balance. The pressure is 100psi. If the 500lb weight is pushed down 2 ins, the

smaller weight is raised 10 ins (2 x5), and vice- versa - this is mechanical gain - the basis of

hydraulic jacks etc.

The fluid used in hydraulics is usually oil though water is used in some applications.

Hydraulic oil often has a number of chemical additives to prevent it from foaming,

deteriorating over time, igniting under heat and pressure, and also to increase lubrication

qualities.

The secret to the remarkable strength of hydraulic equipment is the root formula that

determines hydraulic strength: F = PA, where F= Output Force, P = System Pressure and
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A = Area, whether it is the area of a piston in a hydraulic cylinder or the area of a piston in a

hydraulic pump.

Figure 1. Principle of hydraulics

The power of hydraulic is further enhanced by the fact that it is transmitted over short

distances from one place to another. The motor and pump producing the power can be

located remotely from where the hydraulic actuator is doing the actual work. For this reason,

hydraulically operated equipment appears to be very compact for its strength. Machine

designers are given great flexibility in designing mechanisms when they are able to locate

the source of hydraulic power outside of the actual work area.

The other related equipment in a hydraulic system is also similarly tough and

forgiving of abuse. A properly designed and maintained hydraulic system will provide years

of trouble free, hard working service.

HISTORY OF HYDRAULIC SYSTEM

The history of hydraulic systems takes us into the world of technology and

construction. This is one of those Innovative methods of making work easier and more

efficient by compressing fluids that are locked inside a channel or compartment. This

compression is an applied force or torque and supplies leverage to a workload. Thus the

work load is lessened or made easier. The power steering in cars is a good example of the

use of hydraulic systems. There are countless other hydraulic systems that have come about

since the first use of such systems were invented.

In 1785 and Englander named Joseph Bramah was working on a press. William

Georges Armstrong ( sir - 1st Baron ) a contemporary of Bramah, was an industrialist and

the founder of Armstrong Whitworth. Sir Armstrong is said to have found inspiration in a

water wheel for his later engineering work while he was out on a fishing expedition. He noted


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that while the water wheel was doing much work it was still allowing much potential to be

lost. This lost potential, he reasoned, could be harnessed somehow. He first designed a

rotary engine from the concept but later moved it to an hydraulic piston type of design that

could move a crane.

At a time when the scientific field of hydraulics engineering was not yet recognizedArmstrong and Bramah were applying Pascal's laws to their inventions. Joseph Bramah got

a patent for his invention of the hydraulic press in 1795.

While arguments could be made that would place the use of hydraulic engineering at

a much earlier period in history such as a claim that in the 14 th century Somali tribes used

water forces in agriculture or that even thousands of years ago seafarers used oars as

contraptions or lever to exert force on water, or that in the Greek hellenic period writers were

describing machines that made use of leveraged fluids in force pumps. But history has a well

marked beginning with Bramah and Sir Armstrong.

Since 1795 several engineers and inventors have added their contribution to this scientific

field of science that deals with the subject of forces exerted on fluids or fluid dynamics.

The history of hydraulic systems is found in dam design and engineering. It is found in the

field of automobile, aviation, bicycles, rail. It is found in military applications and space

exploration and in other disciplines where fluid circuitry is used such as turbines, pumps, and

hydropower, The history of hydraulic systems is found in the current development of the

computer where computational fluid dynamics is a buzz term.

This history is found wherever hydraulic machinery and hydraulic cylinders are located.

SCHEMATIC DIAGRAM OF HYDRAULIC SYSTEM

A hydraulic schematic diagram as the name suggests, is a line comprising of

hydraulic symbols. It is a kind of route map of a hydraulic system indicating the placement of

all the components and the way they are connected with each other within circuit.

A schematic diagram of a hydraulic machine is a useful tool for a skilled technician to

interpret the hydraulic symbols and detecting the possible reasons of a problem. In fact,

schematic diagrams help save the costs and time incurred while troubleshooting the

problems.

Hydraulic systems vary in their design from small lifting pumps to systems that fill

compartments on ocean vessels. Possible components include pumps to create high

pressure and move fluid through the system. Pumps can also charge accumulators, which

use compressed gas to store energy and maintain pressure on the system. Actuators
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change the direction hydraulic fluid flows, or stop its flow, to impart translational mechanical

motion upon a component outside the system.

In case a diagram is not available, the technician needs to trace the entire hydraulic

circuit, recognize its components and zero in the potential grounds of problem. Now, given

the complexity of system this whole process can take a lot of time to complete, besides, thepresence of a valve manifold in the circuit can worsen the situation. The valve manifold

needs to be dismantled or removed only to understand the significance of its occupancy

because if the function of a component is not known, its possibility of being the root cause of

problem would multiply quite a few times. A schematic hydraulic map is a simple solution to

escape such a hassle.

The significance of the schematic diagram is most often underestimated and thus, it

is a rare case if a machine owner has the requisite schematic diagram for his hydraulic

system. Being a low rated document, most of the machine owners do not care much about it

and so it gets lost or misplaced. In case a machine is bought second hand, the possibility of

the non-issue of schematic diagrams strengthens all the more.

PARTS OF A HYDRAULIC SYSTEM

The power generating system consists of a group of units whose coordinated action

provides the hydraulic power necessary for the operation of the main hydraulic system. It

consists of the following principal parts:

a. The IMO pumps (1) supply hydraulic power to the system and are driven by

electric motors (2).

b. The main supply tank (6)contains the oil needed to keep the system filled.

c. The accumulator (4), as the name implies, accumulates the oil from the pump and

creates pressure oil which is maintained at a static head for instant use anywhere in the

system.

d. The main supply and return manifolds (7 and 8) act as distribution and receiving

points for the oil used throughout the system.

e. The pilot valve, (5) is a two-port, lap-fitted trunk, cam-operated slide valve, which

directs the flow of oil that causes the automatic bypass valve to open or shut.

f. The automatic bypass and non-return valves (3). The automatic bypass valve

directs the flow of pressure oil in response to the action of the pilot valve. The non-return

valve prevents the oil from escaping through the open automatic bypass.

g. Cut-out valves, serving various purposes throughout the system and non-return

valves to permit one-way flow.


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h. The back-pressure tank, or volume tank (10), contains compressed air at a

pressure of 10 to 25 pounds per square inch, which provides the air pressure on top of the

oil in the main supply tank and maintains the entire system full of oil.

i. The accumulator air flask (9) serves as a volume tank for the accumulator, allowing

the air to pass to and from it when the accumulator is loading or unloading.

Figure 2. Schematic of Hydraulic System

Hydraulic Brake System

When brakes are applied suddenly in a moving vehicle,there is every chance of the

vehicle to skid because the wheels are not retarded uniformly.In order to avoid this danger of

skidding when the brakes are applied,the brake mechanism must be such that each wheel is

equally and simultaneously retarded. A hydraulic brake system serves this purpose. It works

on the principle of Pascal's law.


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Construction of Hydraulic Brake System

Figure 3. Schematic of Hydraulic Brake System

The following figure shows the schematic diagram of a hydraulic brake system. The

hydraulic brake system has a main cylinder filled with brake oil. The main cylinder is provided

with a piston P which is connected to the brake pedal through a lever assembly. A T shaped

tube is provided at the other end of the main cylinder. The wheel cylinder having two pistons

P1 and P2 is connected to the T tube. The pistons P 1 and P2 are connected to the brake

shoes S1 and S2 respectively.

Working of Hydraulic Brake System

When the brake pedal is pressed, piston P is pushed due to the lever assembly

operation. The pressure in the main cylinder is transmitted to P1 and P2. The pistons P1

and P2 push the brake shoes away, which in turn press against the inner rim of the wheel .

Thus the motion of the wheel is arrested. The area of the pistons P1 and P2 is greater than

that of P. Therefore a small force applied to the brake pedal produces a large thrust on the

wheel rim.

The main cylinder is connected to all the wheels of the automobile through pipe line

for applying equal pressure to all the wheels. A figure shows this:


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Figure 4. Hydraulic Brake System

Hydraulic Pump Schematic

The hydraulic pump schematic diagram on the left is for load sensing and pressure

limiting control. The schematic diagram on the right is for load sensing and pressure limiting

control, with power limiter.

Figure 5. Schematic of Hydraulic Pump

TYPES OF HYDRAULIC SYSTEM

Open-Center System

In this system, a control-valve spool must be open in the center to allow pump flow to

pass through the valve and return to the reservoir. In the illustration below, shows this

system in the neutral position. To operate several functions simultaneously, an open-center

system must have the correct connections, such as, series, series/parallel connection, and

flow divider. An open-center system is efficient on single functions but is limited with multiple

functions.


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Figure 6. Open Center System

Open-center System with a Series Connection

Illustrated below, shows an open-center system with a series connection. Oil from a

pump is routed to the three control valves in series. The return from the first valve is routed

to the inlet of the second, and so on. In neutral, the oil passes through the valvesin series

and returns to the reservoir, as the arrows indicate. When a control valve is operated, the

incoming oil is diverted to the cylinder that the valve serves. Return liquid from the cylinder is

directed through the return line and on to the next valve. This system is satisfactory as long

as only one valve is operating at a time. When it happens, the full output of the pump at full

system pressure is available to that function. However, if more than one valve is operating,

the total of the pressure required for each function cannot exceed the systems relief setting.

Figure 7. Open-center system with a series connection


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Open-center System with a Series/Parallel Connection

Illustrated below, shows a variation on the series-connected type. Oil from the pump

is routed through the control valves in series, as well as in parallel. The valves are

sometimes stacked to allow for extra passages. In neutral, a liquid passes through the valves

in series, as the arrows indicate.However, when any valve is operating, the return is closed and the oil is available to

all the valves through the parallel connection. When two or more valves are operated at

once, the cylinder that needs the least pressure will operate first, then the cylinder with the

next least, and so on. This ability to operate two or more valves simultaneously is an

advantage over the series connection.

Figure 8. Open-center system with a series/parallel connection

Closed-Center System

In this system, a pump can rest when the oil is not required to operate a function.

This means that a control valve is closed in the center, stopping the flow of the oil from the

pump.

The illustration below shows a closed-center system. To operate several functions

simultaneously, a closed-center system have the following connections:


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Figure 9. Closed-center system

Hydraulic Cylinders

An actuation device that makes use of a pressurized hydraulic fluid is known as a

hydraulic pump. This mechanism is used for producing in linear motion and force in

applications that transfer power. In other words, a hydraulic cylinder converts the energy

stored in the hydraulic fluid into a force used to move the cylinder in a linear direction.

Operation of a Hydraulic Cylinder

The hydraulic pressure in these cylinders is in the form of hydraulic fuels that are

stored under pressure in these cylinders. The energy stored in these oils is converted intomotion. In a complete hydraulic system, a hydraulic motor consists of one or more hydraulic

cylinders. A pump regulates the oil-flow in the hydraulic system. The pump is a part of the

generator of a hydraulic system. The hydraulic cylinders initiate the pressure of the oil, which

cannot be more than that required by the load.

A hydraulic cylinder consists of a cylindrical barrel, piston, and a piston rod. The

piston that is placed within the barrel is connected to the piston rod. The cylinder bottom, and

the cylinder head, closes the bottom and the head of the barrel respectively. The cylinder

head is the side from where the piston rod exits the cylinder.

The cylinder bottom and the piston rod are mounted with mounting brackets or

clevises. The piston in the hydraulic cylinder consists of sliding rings and seals. The piston

rod chamber and the bottom chamber are the two chambers within the cylinder.

The piston rod starts moving outwards, as the hydraulic fluid is pumped into the

bottom side of the hydraulic cylinder. In the reverse process, the hydraulic fluid is pushed


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back into the reservoir by the piston. The pressure in the cylinder is the ratio of unit force per

unit piston area.

The pressure generated in the piston rod chamber is the ratio of the unit load per the

difference in the unit piston area and unit piston rod area. This calculation is used when the

hydraulic fluid is let into the piston rod chamber as well as the fluid flows smoothly (withoutpressure) from the piston area to the reservoir. In this way, the expansion and retraction

(push and pull) action of the hydraulic cylinder is generated.

Classification of Hydraulic Cylinders According To Function

Single Acting Cylinders

In single acting cylinders the fluid is pressurized from only one side of the cylinder

during both the expansion as well as the retraction process. A spring or an external load is

used to return the cylinder top to its original position i.e. when pressure of the fluid is cut off.

Figure 10. Single Acting Cylinder

Double Acting Cylinders

In the double acting cylinders, the pressure from the fluid is applied in both the

directions. Single cylinders that consist of springs are not used in large stroke applications

because there are inherent mechanical problems associated with the spring. The double

acting rods could be of two types:

Single rod ended

Double rod ended


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Figure 11. Double Acting Cylinder

Classification Of Cylinders According To Specifications

Plunger Cylinders

These cylinders are also known as Ram cylinders. These types of hydraulic cylinders

are placed in an upright position. This is done so that once the supply of the fluid is stopped,

the weight on the cylinder will make it return to its original position. The cylinders used in

automobile service centers are a good example of the plunger cylinders.

Telescoping Cylinders

Telescopic cylinders are also known as multistage hydraulic cylinders. These

cylinders have at the most six stages. These are specially used in applications where there is

less area. Telescopic cylinders can either be single action or double action. The stroke of

these cylinders is long and is used in applications such as cranes and forklifts, etc.

Cable Cylinders

The cable cylinders can either be hydraulic or pneumatic powered cylinders that are

of the double acting type. These cylinders have long strokes and produce moderate force.

The cable cylinders can be operated in limited space.

Diaphragm Cylinders

Diaphragm cylinders are of two types i.e. flat diaphragm and rolling diaphragm.

These cylinders have zero leak around the piston.


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Components of A Hydraulic Cylinder

There are various components that form a part of the hydraulic cylinders.

The various parts are the cylinder bottom, cylinder bottom connection cylinder barrel,

and cylinder head. It also consists of the piston, piston rod, and the piston rod connection.And some of the hydraulic cylinders may comprise of the feet. These are used to mount the

barrels.

The cylinder barrel is a thick tube that has to be machined from the inside. The

interior of the barrel is honed or ground and in some cases both. The cylinder barrel and the

bottom of the cylinder are welded together in most of the hydraulic cylinders.

This welding of the bottom of the cylinder to the barrel can damage the interior of the

barrel. Hence, it is preferred to have the two screwed together. This type of connection will

be helpful during repairs or maintenance of the cylinder barrel. On the other hand, the barrel

is connected to the cylinder head with a lock.

There is a simple lock system used for a simple cylinder. In most of the hydraulic

cylinders the flanged or screwed connections are used. The best type of connections and

most expensive connections are the flanged connections. It is considered to be the best type

of connection because before machining a flange is welded onto the tube.

The other positive aspects are that the flange is always bolted and can be removed

easily when required. The disconnection process as well as the alignment process while

mounting is much tougher for the bigger hydraulic cylinders. This problem in particular arises

where the screw size is between 300 mm to 600 mm.

There should be no bending moments implied on the hydraulic cylinder as they are

applied in expansion and retraction actions. The single clevis connection with a ball bearing

is considered to be the most appropriate connection, as all the above-mentioned problems

do not arise.

Specifications to Be Considered While Purchasing A Hydraulic Cylinder

The specifications that need to be considered while purchasing a hydraulic cylinder

are:

Bore Diameter: It is the diameter of the cylinder bore.

Maximum operating pressure: The maximum working pressure a cylinder can

carry is known as maximum operating pressure.

Rod Diameter: It is the diameter of the piston or the rod that are used in hydraulic

cylinders.


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Stroke: The distance traveled by a piston in a hydraulic cylinder is known as stroke.

The length of a stroke could be several feet, or a fraction of an inch.

Type Of Cylinder: The different types of cylinders are tie-rod cylinder, ram cylinder

and welded cylinder.

Tie-rod cylinder:These types of hydraulic cylinders make use of a single or multiple

tie-rods to provide extra stability to the cylinder. The tie-rods are mostly installed on

the exterior diameter of the cylinder. The tie-rods carry most of the load in this type of

hydraulic cylinder.

Welded cylinder:There are heavy-duty welded cylinders used to balance the

cylinder. The welded cylinders are smooth hydraulic cylinders.

Ram cylinders:As the name suggests, this cylinders act as a ram. The cross-

section of the moving components is half of the cross-section area of the piston rod.

These hydraulic ram cylinders are not used to push and are mostly used to pull. Theram cylinder is a hydraulic cylinder that is used in applications of high pressure.

Types of Hydraulic Pumps

Gear pumps

Gear pumps (with external teeth) (fixed displacement) are simple and economical

pumps. The swept volume ordisplacement of gear pumps for hydraulics will be between

about 1 cm3 (0.001 litre) and 200 cm3 (0.2 litre). These pumps create pressure through the

meshing of the gear teeth, which forces fluid around the gears to pressurize the outlet side.

Some gear pumps can be quite noisy, compared to other types, but modern gear pumps are

highly reliable and much quieter than older models.

Figure 12. Schematic Diagram of Gear Pump
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A gear pump uses the meshing of gears to pump fluid by displacement. They are one

of the most common types ofpumps forhydraulic fluid powerapplications. Gear pumps are

also widely used in chemical installations to pump fluid with a certain viscosity. There are two

main variations; external gear pumps which use two external spur gears, and internal gear

pumps which use an external and an internal spur gear. Gear pumps are positivedisplacement (or fixed displacement), meaning they pump a constant amount of fluid for

each revolution. Some gear pumps are designed to function as either a motoror a pump.

Types of Gear Pump

External Gear Pump

Figure 13. External Gear Pump

External gear pumps are a popular pumping principle and are often used as

lubrication pumps in machine tools, in fluid power transfer units, and as oil pumps in engines.

External gear pumps can come in single or double (two sets of gears) pump

configurations with spur (shown), helical, and herringbone gears. Helical and herringbone

gears typically offer a smoother flow than spur gears, although all gear types are relatively

smooth. Large-capacity external gear pumps typically use helical or herringbone gears.

Small external gear pumps usually operate at 1750 or 3450 rpm and larger models operate

at speeds up to 640 rpm.
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Figure 14. Schematic of External Gear Pump

External gear pumps have close tolerances and shaft support on both sides of the

gears. This allows them to run to pressures beyond 3,000 PSI / 200 BAR, making them well

suited for use in hydraulics. With four bearings in the liquid and tight tolerances, they are notwell suited to handling abrasive or extreme high temperature applications.

Tighter internal clearances provide for a more reliable measure of liquid passing

through a pump and for greater flow control. Because of this, external gear pumps are

popular for precise transfer and metering applications involving polymers, fuels, and

chemical additives.

How External Gear Pumps Work

External gear pumps are similar in pumping action to internal gear pumps in that two

gears come into and out of mesh to produce flow. However, the external gear pump uses

two identical gears rotating against each other -- one gear is driven by a motor and it in turn

drives the other gear. Each gear is supported by a shaft with bearings on both sides of the

gear.

As the gears come out of mesh, they create expanding volume on the inlet side of

the pump. Liquid flows into the cavity and is trapped by the gear teeth as they rotate.

Liquid travels around the interior of the casing in the pockets between the teeth and

the casing -- it does not pass between the gears.

Finally, the meshing of the gears forces liquid through the outlet port under pressure.

Because the gears are supported on both sides, external gear pumps are quiet-

running and are routinely used for high-pressure applications such as hydraulic

applications. With no overhung bearing loads, the rotor shaft can't deflect and cause

premature wear.


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Advantages

High speed

High pressure

No overhung bearing loads

Relatively quiet operation

Design accommodates wide

variety of materials

Disadvantages

Four bushings in liquid area

No solids allowed

Fixed End Clearances

Applications

Common external gear pump applications include, but are not limited to:

Various fuel oils and lube oils

Chemical additive and polymer metering

Chemical mixing and blending (double pump)

Industrial and mobile hydraulic applications (log splitters, lifts, etc.)

Acids and caustic (stainless steel or composite construction)

Low volume transfer or application

Materials Of Construction / Configuration Options

As the following list indicates, rotary pumps can be constructed in a wide variety of

materials. By precisely matching the materials of construction with the liquid, superior life

cycle performance will result.

External gear pumps in particular can be engineered to handle even the most aggressive

corrosive liquids. While external gear pumps are commonly found in cast iron, newer

materials are allowing these pumps to handle liquids such as sulfuric acid, sodium

hypochlorite, ferric chloride, sodium hydroxide, and hundreds of other corrosive liquids.

Externals (head, casing, bracket) - Iron, ductile iron, steel, stainless steel, high alloys,

composites (PPS, ETFE)

Internals (shafts) - Steel, stainless steel, high alloys, alumina ceramic

Internals (gears) - Steel, stainless steel, PTFE, composite (PPS)

Bushing - Carbon, bronze, silicon carbide, needle bearings Shaft Seal - Packing, lip seal, component mechanical seal, magnetically-driven pump


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Figure 15. Composite External Gear Pump

Rotary vane pumps

Rotary vane pumps (fixed and simple adjustable displacement) have higher

efficiencies than gear pumps, but are also used for mid pressures up to 180 bars in general.

Some types of vane pumps can change the centre of the vane body, so that a simpleadjustable pump is obtained. These adjustable vane pumps are in general constant pressure

or constant power pumps: the displacement is increased until the required pressure or power

is reached and subsequently the displacement or swept volume is decreased until

equilibrium is reached.

Figure 16. Rotary Vane Pump

Screw pumps

Screw pumps (fixed displacement) are a double Archimedes spiral, but closed. This

means that two screws are used in one body. The pumps are used for high flows and

relatively low pressure (max 100 bar). They were used on board ships where the constant

pressure hydraulic system was going through the whole ship, especially for the control ofball
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valves, but also for the steering gear and help drive systems. The advantage of the screw

pumps is the low sound level of these pumps; the efficiency is not that high.

Figure 17. Screw Pumps

Theory

Screw pumps are a unique type of rotary positive displacement pump in which the

flow through the pumping elements is truly axial. The liquid is carried between the screw

threads on one or more rotors. The liquid is then displaced axially as the screws rotate and

mesh. In other types of rotary pumps, the liquid is forced to travel circumferentially, however

the screw pump has an axial flow pattern and low internal velocities.

Figure 18. Circumferential Flow

It provides a number of advantages in many applications where liquid agitation or

churning is objectionable. Screw pumps are classified as two different types: the single rotor

and the multiple rotor. The multiple rotor is further divided into timed and untimed categories.

Timed rotors rely on outside means for phasing the mesh of the threads and for supporting

the forces acting on the rotors. Untimed rotors rely on precision and accuracy of the screw

forms for proper mesh and transmission of rotation (Fraser, et. al., 1986.).
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History

The screw pump is the oldest type of pump. The first applications, dating back to the

third century B.C., included irrigation and land drainage. The screw pump is thought to have

been first used in Egypt (Ewbank, 1972). After several other types of pumps were invented,

the screw pump was not used as much because these other pumps could handle higherhead capacities. However, later it was found that these pumps could not handle wastewater

like the screw pump could. Because of this, the screw pump became widely used for such an

application. The Dutch were the first to design a spiral lift screw in 1955. After this, double

screw units were put into operation for flood control in the Netherlands and in municipal

sewage installations in Europe. Based on excellent results from the pumps used in Europe,

the trend extended to Canada and United States and are currently used today

(Cheremisinoff, et. al., 1992).

Applications

There are several applications of the screw pump that include a wide range of

markets: utilities fuel oil service, industrial oil burners, lubricating oil service, chemical

processes, petroleum and crude oil industries, power hydraulics, and many others (Fraser,

et. al., 1986). Listed below are some typical situations where a screw pump is used. The

benefits of using a screw pump in each of these situations are discussed (Cheremisinoff, et.

al., 1992).

Raw sewage lift stations: Can handle variety of raw sewage influent, are non-

clogging, require little attention, are resistant to motor overloads, and are not affected

by running dry

Sewage plant lift stations: Used for sewage lifts up to 40 feet and have self-regulating

lift capacity (Normal lifts are 30 feet, while high lifts are 40 feet high.)

Return activated sludge: Little floc disintegration, nonturbulent discharge into effluent

channel, low horsepower requirements, improved activated sludge treatment.

Stormwater pumping: Are ideal because of large capacity at low heads, no

prescreening necessary

Land Drainage: Used for flood control, can pump large volumes of water over levees.

Three Basic Types

Single Screw

The single screw pump is more commonly known as the Archimedean screw. It is

quite large; typical dimensions include a diameter of 12 inches or greater, and a length up to


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about 50 feet. It is normally used as a water-raising pump with the screw arranged at an

angle of 30 degrees. It can also be used for handling liquids containing solids in suspension

with either vertical lift or horizontal transport. The design of single screw pumps allows very

little fracturing of particles and little abrasion damage to the pump. One disadvantage is the

considerable bulk necessary to achieve high capacities since rotational speeds are of theorder of 30-60 rpm (Warring, 1984).

Figure 19. Single Screw Pump

Intermeshing Screw Pump

The intermeshing screw pump is commonly called a rigid-screw pump. This type of

pump is suitable for a wide range of sizes, and can be run at high speeds. The larger screw

pumps are used for bulk handling of oils and similar fluids. The basic type is suitable for

handling most clean fluids with low flow velocities and at low heads (Warring, 1984).

Eccentric screw pump

The eccentric screw pump is versatile. It is capable of handling a variety of liquids

and products with high efficiency. It comprises of a rigid screw form rotor rolling in a resilient

internal helical stator of hard or soft rubber with a moderately eccentric motion. It can handle

viscous liquids, slurries, pastes, solids in suspension, and delicate products. This is because

of the low flow velocities through the pump (Warring, 1984).

Capacity

The delivered capacity of any screw pump is the theoretical capacity minus the

internal leakage. In order to find the capacity of a screw pump the speed of the pump must

be known. The delivered capacity of any rotary screw pump can be increased several

different ways. The capacity can be increased by simply increasing the speed, increasing the

viscosity, or decreasing the differential pressure. The capacity of the pump depends on

several factors (Cheremisinoff, et. al., 1992):

Diameter of the screw


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Speed of the screw

Number of flights mounted on the screw shaft

o Flights: Single, double, and triple flights are often used. Flights are also

known as helixes. With each increase in flights, there is a 20% increase in

capacity. Therefore, a single flight pump has a capacity that is 80% of a

double flight pump, which in turn has a capacity that is 80% of a triple flight

capacity. The three-flight pump can handle the most capacity in the least

amount of space.

Angle of inclination of the screw

o The greater the angle of inclination, the lower the output. The output lowers

approximately 3% for every degree increase over a 22 inclination.

Level of influent in the influent chamber

Ratio of the diameter of the screw shaft to the outside diameter of the screw flights Clearance between screw flights and trough

Advantages

1. Wide range of flows and pressures

2. Wide range of liquids and viscosities

3. Built-in variable capacity

4. High speed capability allowing freedom of driver selection

5. Low internal velocities

6. Self-priming with good suction characteristics

7. High tolerance for entrained air and other gases

8. Minimum churning or foaming

9. Low mechanical vibration, pulsation-free flow, and quiet operation

10. Rugged, compact design -- easy to install and maintain

11. High tolerance to contamination in comparison with other rotary pumps (Fraser, et.

al., 1986)

Disadvantages

1. Relatively high cost because of close tolerances and running clearances

2. Performance characteristics sensitive to viscosity change

3. High pressure capability requires long pumping elements (Fraser, et. al., 1986


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Bent axis pumps

Figure 20. Bent Axis Pumps

Bent axis pumps, axial piston pumps and motors using the bent axis principle, fixed

or adjustable displacement, exists in two different basic designs. The Thoma-principle

(engineer Hans Thoma, Germany, patent 1935) with max 25 degrees angle and the

Wahlmark-principle (Gunnar Axel Wahlmark, patent 1960) with spherical-shaped pistons in

one piece with the piston rod, piston rings, and maximum 40 degrees between the driveshaft

centerline and pistons (Volvo Hydraulics Co.). These have the best efficiency of all pumps.

Although in general the largest displacements are approximately one litre per revolution, if

necessary a two-liter swept volume pump can be built. Often variable-displacement pumps

are used, so that the oil flow can be adjusted carefully. These pumps can in general work

with a working pressure of up to 350420 bars in continuous work.

Axial piston pumps swashplate principle

Axial piston pumps using the swashplate principle (fixed and adjustable

displacement) have a quality that is almost the same as the bent axis model. They have the
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advantage of being more compact in design. The pumps are easier and more economical to

manufacture; the disadvantage is that they are more sensitive to oil contamination.

Figure 21. Implementation of axial piston pump

Radial piston pumps

Radial piston pumps (fixed displacement) are used especially for high pressure and

relatively small flows. Pressures of up to 650 bar are normal. In fact variable displacement is

not possible, but sometimes the pump is designed in such a way that the plungers can be

switched off one by one, so that a sort of variable displacement pump is obtained.

Figure 22. Radial Piston Pump

Peristaltic pumps

Peristaltic pumps are not generally used for high pressures. A peristaltic pump, or

roller pump, is a type of positive displacement pump used for pumping a variety offluids. The

fluid is contained within a flexible tube fitted inside a circular pump casing (though linear
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peristaltic pumps have been made). A rotorwith a number of "rollers", "shoes" or "wipers"

attached to the external circumference compresses the flexible tube. As the rotor turns, the

part of tube under compression closes (or "occludes") thus forcing the fluid to be pumped to

move through the tube. Additionally, as the tube opens to its natural state after the passing

of the cam ("restitution" or "resilience") fluid flow is induced to the pump. This process iscalled peristalsis and used in many biological systems such as the gastrointestinal tract. It

was invented by the world-famous heart surgeon Dr. Michael DeBakey while he was a

medical student in 1932.

Figure 23. Schematic diagram of Peristaltic Pump

Pumps for Open and Close Systems

Most pumps are working in open systems. The pump draws oil from a reservoir

at atmospheric pressure. It is very important that there is no cavitation at the suction side of

the pump. For this reason the connection of the suction side of the pump is larger in

diameter than the connection of the pressure side. In case of the use of multi-pump

assemblies, the suction connection of the pump is often combined. It is preferred to have

free flow to the pump (pressure at inlet of pump at least 0.8 bars). The body of the pump is

often in open connection with the suction side of the pump.

In case of a closed system, both sides of the pump can be at high pressure. The

reservoir is often pressurized with 6-20 bars boost pressure. For closed loop systems,

normally axial piston pumps are used. Because both sides are pressurized, the body of the

pump needs a separate leakage connection.

Multi Pump Assembly

In a hydraulic installation, one pump can serve more cylinders and motors. The

problem however is that in that case a constant pressure system is required and the system

always needs the full power. It is more economic to give each cylinder and motor its own

pump. In that case multi pump assemblies can be used. Gearpumps can often be obtained
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as multi pumps. The different chambers (sometimes of different size) are mounted in one

body or built together. Also vane pumps can often be obtained as a multi pump. Gerotor

pumps are often supplied as multi pumps. Screw pumps can be built together with a gear

pump or a vane pump. Axial piston swashplate pumps can be built together with a second

pump of the same or smaller size, or can be built together with one or more gear pumps orvane pumps (depending on the supplier). Axial plunger pumps of the bent axis design can

not be built together with other pumps.

The different types of Hydraulic control valves

1. Closed control - When a nozzle is in neutral position, it would automatically stop the

pump flow to the tank.

2. Parallel - In this valve the oil flow is divided equally on the consideration that the

operating pressure requirements are the same for all functions.

3. Open center- This valve connects the pump flow to the tank, when the valve spool

is in neutral position

4. Four way - These valves are most commonly known as the double acting valve.

They have four functional port connections. The ports consist of two work ports a

"pump" port and a "tank" port.

5. Free flow - The design of this valve is in such a way such so as to facilitate the flow

from "work" ports to "tank" while in neutral position.

6. Three way - They are mostly called as single-acting valve. They have three

functional port connections.

Types of Hydraulic Fluids

Petroleum-based Fluids

The most common hydraulic fluids used in shipboard systems are the petroleum-

based oils. These fluids contain additives to protect the fluid from oxidation (antioxidant), to

protect system metals from corrosion (anticorrosion), to reduce tendency of the fluid to

foam (foam suppressant), and to improve viscosity. Petroleum-based fluids are used in

surface ships electrohydraulic steering and deck machinery systems, submarines

hydraulic systems, and aircraft automatic pilots, shock absorbers, brakes, control

mechanisms, and other hydraulic systems using seal materials compatible with petroleum-

based fluids.

Synthetic Fire-resistant Fluids


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Petroleum-based oils contain most of the desired properties of a hydraulic liquid.

However, they are flammable under normal conditions and can become explosive when

subjected to high pressures and a source of flame or high temperatures. Nonflammable

synthetic liquids have been developed for use in hydraulic systems where fire hazards exist.

Phosphate Ester Fire-Resistant Fluid

These fluids will burn if sufficient heat and flame are applied, but they do not support

combustion. Drawbacks of phosphate ester fluids are that they will attack and loosen

commonly used paint and adhesives, deteriorate many types of insulations used in electrical

cables, and deteriorate many gasket and seal materials.

APPLICATIONS

Hydraulic systems use an incompressible fluid, such as oil or water, to transmit force

from one location to another. Hydraulic power can multiply an applied force to permit the

lifting or moving of heavy objects, and because of this ability, there are limitless opportunities

to use hydraulic power in industry.

Hydraulics is used in many ways. Most of them are used every day and not even

thought about. Here are some examples of how hydraulics are used.

Figure 24. Hydraulic System

A. Hydraulic Lift Application

As far as science is concerned, the concept of hydraulics is a vital discovery in the

field of engineering. Thanks to Blaise Pascal, the development of vital engineering concepts

provided by the mechanical properties of liquids was brilliantly advanced. The following are

some of the innovations that benefit from the discovery and development of the concept of

hydraulics and hydraulic lifts.

1. Jacks
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The water pressure mechanism in hydraulic car jacks provides an easier and less

strenuous way of lifting a car. It is almost effortless to pump a hydraulic car jack if you try to

compare it with cranking the screw of a mechanical jack. Hydraulic car jacks have definitely

changed how we view changing flat tires and getting underneath our cars.

Figure 25. Jacks

Hydraulic jacks, however, aren't limited to portable car jacks only. They can also be

found in the form of bulky auto lifts found in most car repair shops. Usually, this type of lift is

basically used to lift the whole car so that mechanics can easily access beneath it without

having any troubles of crawling underneath.

2. Wheelchair Lift

A wheelchair lift is a type of lift that is specifically design for the physically-

challenged. The wonders of hydraulic lifts can be of great help for their situation, especially

when they need to descend or ascend from a flight of stairs or any type of elevation for that

matter. Instead of using bulky ramps that can cause great hassles just by mere installation,

they can easily take advantage of the service hydraulic wheelchair lifts offer.


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Figure 26. Wheelchair Lift

3. Short Elevator/Residential Elevator

Before, residential elevators were considered a luxury, something only the affluent

can enjoy. But now, they are increasingly becoming a necessity in most two-story homes

though their prices remain undeniably high. Since people today tend to live in a fast-paced

dimension, everything should come in an instant, and no precious time should be wasted.

Unlike elevators that can be found in commercial buildings, the residential elevator

only travels short distances, approximately 2-4 floors per house. And similar to what the

wheelchair lift offers, this type of elevator offers more accessibility for people who have

mobility problems. This type of lift may often be mistaken as a wheelchair lift, but it isdifferent. They may have the same basic function, but their differences are apparent in their

respective appearances.

Figure 27. Elevator

B. Hydraulic Application on Brakes


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Car Brakes

Car brakes work when you push the brake pedal, it pushes the small piston. The

piston applies pressure on the brake fluid, which press the brake pads on the large pistons.

The brake pads come into contact with the brake drum and slows the car down, eventually

stopping the car.

Bike Brakes

Many bikes are installed with a brake Levers which are usually placed in a bikes

handlebars for easy access on the riders hand whether it is a road bike or a mountain bike.

As the biker activates the brake lever, it instantly transmits force through a mechanical or

hydraulic brake system.

Bicycles with drop handlebars may be equipped with more than one brake lever for

each of its brakes to properly facilitate the braking from any hand positions. There are many

kinds of brake levers that a biker can choose from which is the extension levers and interrupt

brake levers.

Hydraulic brake levers functions through the movement of a piston in the fluid

reservoir. Many bikers have mentioned that hydraulic brake levers are better used with the

appropriate brake system design.

Figure 28. Bike brakes lever

C. Hydraulics on Robots

Robot "muscles" are typically made of hydraulic cylinders that are filled with fluids.

When the hydraulic fluid flows into hydraulic cylinders, the increased pressure pushes the

piston at the other end. Fluid power has the highest power density of any technology.
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Figure 29. Hydraulically operated robot

The purpose of robotics technology is essentially to carry out repetitive, physically

demanding and potentially dangerous manual activities so that humans are relieved from

these tasks. Examples of these chores include working on factory production line assembly,

handling hazardous materials and dealing with hostile environments like mines, underwater

construction sites and even other planets like Mars.

Figure 30. Robotic arm

D. Hydraulic Application on Airplanes and Board Ships

Airplanes

Airplanes and jet planes use hydraulics in many places.

Adjusting wings

Putting out/bringing in landing gear

Opening/closing doors

Board ships


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We all know that a ship is a mobile power plant. It has enormous varieties of

machineries for its propulsion, cargo operations, and shipboard safety as well as for

maintaining the comfort standards of the crew. In all this wide variety of machinery,

hydraulics plays a very vital role. The hydraulic technology is so precise and accurate that

they are used in the main engine control and maneuvering systems, too. Let us now discusson some important hydraulic applications on board ships and a short description of each.

1. Deck Machineries

Deck machineries include the deck cranes, winches, mooring drums, windlass,

capstans, emergency towing arrangements, hatch covers, and other similar equipment. All

these machineries have very simple and basic hydraulic systems involved in smoother and

heavy duty operation. In ships like bulk carriers that unload the cargo, it requires either a

deck crane or a derrick, which is usually controlled by an electro-hydraulic system. The

mooring winches are the machineries that keep the ship tied up to the jetty or to another

ship. The anchor is dropped and ship is held in a place by the windlass. They all have

hydraulic motors and source of hydraulic oil under high pressure.

Figure 31. Deck Machineries

2. Ship Stability

These ships have fish like fins called stabilizers that act as a resistance against

rolling. These operate under high hydraulic oil pressure and thus reduce rolling to very great

extent, making the life on board a cruise ship more comfortable.


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Figure 32. Ship Operating under Hydraulic Oil Pressure

3. Steering Gears

Figure 33. Steering Gears

Small boats may have a wire attached to the steering wheel and rudder, thus helping

in steering the ship. This can be compared to the normal steering of a car against a power

steering using hydraulics. As the size of ships increased, mechanical and other means ofsteering experienced problems and, thus, electro-hydraulic steering gears are being used.

4. Bow and Stern Thrusters

The biggest container ship in the world is of the size 14000 TEUs. It is not possible

for these ships to deliver cargo, maneuvering in restricted waters, without the bow and stern

thrusters. As we know, a bow and stern thruster is a propeller which has a transverse axis of

rotation instead of longitudinal axis. To alter the pitch of these thrusters, hydraulics is used,

and they perform a very precise and accurate control, thus enabling the ship to maneuver

easily.
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Figure 34.Bow and Stern Thruster

E. Hydraulic Cylinder

A hydraulic cylinder is a mechanical actuator that is used to give a

unidirectional force through a unidirectional stroke. It has many applications, notably

in engineering vehicles.

Agricultural Equipment Construction Equipment

Airport Ground Supporting Equipment Waste Management Equipments

Figure 35. Applications of Hydraulic Cylinders

Hydraulic cylinders get their power from pressurized hydraulic fluid, which is typically

oil. The hydraulic cylinder consists of a cylinder barrel, in which a piston connected to a

piston rod moves back and forth. The barrel is closed on each end by the cylinder bottom

(also called the cap end) and by the cylinder head where the piston rod comes out of the

cylinder. The piston has sliding rings and seals. The piston divides the inside of the cylinder

in two chambers, the bottom chamber (cap end) and the piston rod side chamber (rod end).

The hydraulic pressure acts on the piston to do linear work and motion.
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F. Hydraulic Machines

Hydraulic pressA combination of a large and a small cylinder connected by a pipe and filled with a

fluid so that the pressure created in the fluid by a small force acting on the piston in the small

cylinder will result in a large force on the large piston.

The operation depends upon Pascal's principle, which states that when a liquid is at

rest the addition of a pressure (force per unit area) at one point results in an identical

increase in pressure at all points.

Figure 36. Hydraulic jack

The principle of the hydraulic press is used in lift jacks, earth-moving machines, and

metal-forming presses. A comparatively small supply pump creates pressure in the hydraulic

fluid. The fluid then acts on a substantially larger piston to produce the action force. Heavyobjects are accurately weighed on hydraulic scales in which precision-ground pistons

introduce negligible friction.

Based on the nature ofwork, a hydraulic press may be modified to suit the need.

Hydraulic press used in industries are generally converted or built to crush or to press any

process or the product".
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For example, this may include steel plates, aluminum rolls, metallic ores, etc. In this

article, we will discuss the general principle of hydraulic presses followed by the details of the

actual industrial hydraulic press.

Figure 37. Principle of Hydraulic Press

The system is a very simple example which demonstrates the operation of a basic

hydraulic system. It has two simple cylinders connected to each other, containing an

adequate quantity of hydraulic fluid in it. One of the cylinders is larger in size when compared

to the other.Both the cylinders have pistons in them, but in strict hydraulic terminology, the larger

piston is called as a ram and small one a plunger.

As seen from figure, a small force P applied on the plunger, in the downward

direction, presses the hydraulic fluid below it.
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Figure 38. Hydraulics

Used in Heavy Equipments

The force applied on the plunger may be small when compared to the weight placed

on the ram. Also, the area of the plunger is small when compared to area of the ram. But the

pressure acting on the plunger (due to the application of force F on the plunger), and the

ram is same (Pascals Law). It is the area on which the pressure is acting that makes the

difference. The pressure P acts on the ram, which has a large area. The same pressure P

acting on the plunger has a small area. Also the distance traveled by the plunger is more

when compared to the distance traveled by the ram. This makes a small force applied on the

plunger able to lift heavy loads placed on the ram.

TROUBLESHOOTING

The troubleshooting charts and maintenance hints that follow are of a general systemnature but should provide an intuitive feeling for a specific system. More general information

is covered in the following paragraphs. Effect and probable cause charts appear on the

following pages.

There is, of course, little point in discussing the design of a system which has been

operating satisfactorily for a period of time. However, a seemingly uncomplicated procedure

such as relocating a system or changing a component part can cause problems. Because of

this, the following points should be considered:

1. Each component in the system must be compatible with and form an integral part of

the system. For example, an inadequate size filter on the inlet of a pump can cause

cavitation and subsequent damage to the pump.

2. All lines must be of proper size and free of restrictive bends. An undersized or

restricted line results in a pressure drop in the line itself.


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3. Some components must be mounted in a specific position with respect to other

components or the lines. The housing of an in-line pump, for example, must remain

filled with fluid to provide lubrication.

4. The inclusion of adequate test points for pressure readings, although not essential for

operation, will expedite troubleshooting.

Knowing the System

Probably the greatest aid to troubleshooting is the confidence of knowing the system.

The construction and operating characteristics of each one should be understood. For

example, knowing that a solenoid controlled directional valve can be manually actuated will

save considerable time in isolating a defective solenoid. Some additional practices which will

increase your ability and also the useful life of the system follow:

1. Know the capabilities of the system. Each component in the system has a maximum

rated speed, torque or pressure. Loading the system beyond the specifications simply

increases the possibility of failure.

2. Know the correct operating pressures. Always set and check pressures with a gauge.

The correct operating pressure is the lowest pressure which will allow adequate

performance of the system function and still remain below the maximum rating of the

components and machine.

3. Know the proper signal levels, feedback levels, and dither and gain settings in servo

control systems. If they arent specified, check them when the system is functioning

correctly and mark them on the schematic for future reference.

Developing Systematic Procedures

Analyze the system and develop a logical sequence for setting valves, mechanical

stops, interlocks and electrical controls. Tracing of flow paths can often be accomplished by

listening for flow in the lines or feeling them for warmth. Develop a cause and effect

troubleshooting guide similar to the charts appearing on the following pages. The initial time

spent on such a project could save hours of system down-time.

Recognizing Trouble Indications

The ability to recognize trouble indications in a specific system is usually acquired

with experience. However, a few general trouble indications can be discussed.

1. Excessive heat means trouble. A misaligned coupling places an excessive load on

bearings and can be readily identified by the heat generated. A warmer than normal

tank return line on a relief valve indicates operation at relief valve setting. Hydraulic


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fluids which have a low viscosity will increase the internal leakage of components

resulting in a heat rise. Cavitation and slippage in a pump will also generate heat.

2. Excessive noise means wear, misalignment, cavitation or air in the fluid. Contaminated

fluid can cause a relief valve to stick and chatter. These noises may be the result of

dirty filters, or fluid, high fluid viscosity, excessive drive speed, low reservoir level,loose intake lines or worn couplings.

The following charts are arranged in five main categories. The heading of each one

is an effect which indicates a malfunction in the system.

For example, if a pump is exceptionally noisy, refer to Chart 1 titled Excessive Noise.

The noisy pump appears in Column A under the main heading. In Column A there are four

probable causes for a noisy pump. The causes are sequenced according to the likelihood of

happening or the ease of checking it. The first cause is cavitation and the remedy is a.

Remedies for Excessive Noise

a. Any or all of the following:

replace dirty filters; wash strainers in solvent compatible with system fluid;

clean clogged inlet line;

clean or replace reservoir breather vent;

change system fluid; change to proper pump drive motor speed;

overhaul or replace supercharge pump;

fluid may be too cold.

b. Any or all of the following:

tighten leaking connections;

fill reservoir to proper level (with rare exception all return lines should be below

fluid level in reservoir);

bleed air from system;

replace pump shaft seal (and shaft if worn at seal journal).

c. Align unit and check condition of seals, bearings and coupling.

d. Install pressure gauge and adjust to correct pressure.

e. Overhaul or replace


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c. Align unit and check condition of seals and bearings; locate and correct mechanical

binding; check for work load in excess of circuit design.

d. Install pressure gauge and adjust to correct pressure (keep at least 125 PSI difference

between valve settings).

e. Overhaul or replace.f. Change filters and also system fluid if improper viscosity; fill reservoir to proper level.

g. Clean cooler and/or cooler strainer; replace cooler control valve; repair or replace

cooler.

Figure 40. Remedies for Excessive Heat

Remedies for Incorrect Flow

a. Any or all of the following:

replace dirty filters;


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clean clogged inlet line;

clean or replace reservoir breather vent;

fill reservoir to proper level;

overhaul or replace supercharge pump.

b. Tighten leaking connections.

c. Check for damaged pump or pump drive; replace and align coupling.

d. Adjust.

e. Overhaul or replace.

f. Check position of manually operated controls; check electrical circuit on solenoid

operated controls; repair or replace pilot pressure pump.

g. Reverse rotation.

h. Replace with correct unit.


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Figure 41. Remedies for Incorrect Flow

Remedies for Incorrect Pressure

a. Replace dirty filters and system fluid.

b. Tighten leaking connections (fill reservoir to proper level and bleed air from system).


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Figure 42. Remedies for Incorrect Pressure

Remedies for Faulty Operations

a. Fluid may be too cold or should be changed to clean fluid of correct viscosity.

b. Locate bind and repair.

c. Adjust, repair or replace.

d. Clean and adjust or replace; check condition of system fluid and filters.

e. Overhaul or replace.

f. Repair command console or interconnecting wires.

g. Lubricate.

h. Adjust, repair or replace counterbalance valve


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Figure 43. Remedies for Faulty Operation

MAINTENANCE

Three simple maintenance procedures have the greatest effect on hydraulic system

performance, efficiency and life.

1. Maintaining a clean sufficient quantity of hydraulic fluid of the proper type and

viscosity.

2. Changing filters and cleaning strainers.

3. Keeping all connections tight, but not to the point of distortion, so that air is excluded

from the system.


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Sound Advice

Producing quiet, hydraulically-actuated machines requires more than just the use of

quiet components. Meeting the stringent sound-level specifications of todays industrial

hydraulic systems and machines takes careful engineering. The pump should be considered

first. It not only produces sound directly but generates vibrations and fluid pulsations. Thesereact with other machine parts which produce more sound.

Mechanical Isolation

To meet lower sound level limits, the pump should be mechanically isolated from the

rest of the machine using anti-vibration mountings. This also requires that all connections to

the pumps be made with flexible hose.

Flexible hose will often reduce noise even where anti-vibration mountings are not

used. It prevents vibrations from reaching other lines and components to keep them from

becoming sound sources. In long lengths, this hose is itself, a good sound generator so only

short lengths should be used. For long runs, use solid pipes with short hoses at the ends. All

long lines must be supported every meter or so, preferably with clamps providing vibration

damping. Lines must not contact panels that are good sounding boards. Where they pass

through such panels, allow sufficient clearance to prevent direct contact; never use bulkhead

fittings in such cases.

Acoustic Isolation

The greatest sound level reductions are attained with the pump acoustically as well

as mechanically isolated. This requires that the pump be completely enclosed in a non-

porous shell weighing at least 10 kg per square meter of surface. No openings can be

tolerated and all joints must be sealed with resilient gaskets or moldings.

Grommets of rubber or other soft material should be used to close openings around

piping and to prevent mechanical contact between the enclosure and piping. It must be

emphasized that while mechanical isolation by itself can reduce noise, acoustic isolation can

only be effective when used in combination with mechanical isolation.

Fluids

The condition of the fluid being pumped is also important in controlling sound. Fluid

viscosity, temperature and vacuum by themselves have no effect on sound levels. It is

important to control them, however, to prevent the formation of entrained air or vapour

bubbles that can double sound levels, and reduce pump life.


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A combination of high fluid temperature and inlet vacuum generates what are called

cavitation bubbles. However, at low temperatures, a high viscosity fluid in a very long suction

line can also produce sufficient vacuum to cause cavitation. Important methods of

suppressing bubble formation include: Using short runs or large diameter inlet lines; keeping

the reservoir elevation close to or above that of the pump; using low pressure-drop inletfilters that signal when they are producing high vacuums and need changing; and, providing

adequate fluid controls. These are all good hydraulic practices that become increasingly

important where you must achieve low sound levels.

SWOT ANALYSIS

STRENGTHS

Today's hydraulic presses are faster and more reliable then ever. In the last decade,

the technology has gone through constant change. Improvements in seals, more efficient

pumps, and stronger hoses and couplings have virtually eliminated leaks and minimized

maintenance.

Programmable logic controllers (PLCs) and other electronically-based controls have

improved speed and flexibility. With new computer interfaces and monitoring, hydraulic

presses are now widely used in advanced computer-integrated manufacturing systems.

The primary advantage of hydraulic systems compared to pneumatic and electric

systems is that high forces and torques can be developed with comparatively compact

motors without the need for gearboxes. Very accurate motion controls are possible using

sophisticated servo valves.

Here are some other advantages of using hydraulics in multiple applications.

Small and Light

Hydraulic equipment such as hydraulic pumps, cylinders, motors, etc., is able to

provide a huge amount of power from a very small machine by using high hydraulicpressure. Pneumatic systems, unlike hydraulic systems, cannot hold a load in place rigidly,

as the air in pneumatic systems is compressible and hydraulic fluid isn't. Hydraulic systems

take up less room than pneumatic systems.


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Force Multiplication

You can adjust the amount of force by the design of the driving piston. This is also

very useful in the above auto and airplane applications.

Easily Remote Controlled

Because mechanical cranes use a lever, rod, link and chain for the control system,

the controls must be placed close to the mechanism. For hydraulic cranes, it is only

necessary to connect the control valves to the mechanism using pipes, so the controls can

be placed far away.

Easy to Changed Speed

Because mechanical cranes use a lever, rod, link and chain for the controlsystem, the controls must be placed close to the mechanism. For hydraulic cranes, it is only

necessary to connect the control valves to the mechanism using pipes, so the controls can

be placed far away.

Most electric motors (in electric energy systems) operate at a constant

speed. In the energy system of hydraulic, hydraulic motors can also be operated at a

constant speed. Nevertheless the working elements (both linear and rotary) can be run at a

speed of changing in a way to change the volume of drainage / discharge, or by using the

flow control valve.

Downtime Reduced

In addition to accomplishing a task faster, hydraulics also can contribute to

decreased downtime. Grease is a dirty word to many, not because of its grimy connotations,

but because contractors are all too familiar with the work stoppages necessary to ensure that

equipment is properly greased or lubricated at various intervals, along with the

consequences of neglecting this task. Fortunately for the operator of a handheld hydraulic

breaker, the hydraulic oil providing the power also is supplying constant lubrication during

operation, taking the task of greasing out of the operators hands. A similar pneumatic toolwould need to be regularly oiled during use. Not only does this difference maximize uptime,

but also minimizes risk of equipment being damaged due to inadequate lubrication.

Hydraulics also reduces downtime on jobs during the winter. While the oil powering

hydraulic tools will quickly warm to working temperature, condensation on pneumatic tools


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can sometimes cause the exhaust ports to freeze up in cold weather if some sort of

antifreeze is not used. For all contractors, stoppages and downtime cost money.

Plug and Play

Hydraulics also provides benefits for interior or confined-space work. Pneumatics is

not a good choice under either of these circumstances, due to the exhaust ports on air-powered tools creating both dust and noise pollution. With hydraulics working in a closed

circuit, exhaust fumes and sound are kept to a minimum, making work conditions much

safer.

While hydraulic tools are generally friendlier from an operators perspective, they also

are environmentally friendly. Fuel consumption is drastically lower on a hydraulic power pack

compared with an air compressor, which has more cylinders and requires higher horsepower

to produce sufficient air to operate pneumatic tools. In some cases, air compressors will use

up to eight times as much fuel as comparable hydraulic power packs, which affects the

financial side of a contractors operation in addition to the environmental aspect of the job.

To further reduce any potential environmental effects, some hydraulic-equipment

manufacturers design their power packs and hydraulic tools to work with biodegradable oil.

This minimizes any sort of jobsite contamination risks. It also means that no special permits

are required for discarding the oil, thereby keeping the task of oil disposal simple for the

contractor.

Cost

Pneumatic systems tend to be simpler than hydraulic systems, and therefore less

expensive to purchase and install. However, their operating costs tend to be higher than

those of hydraulic systems, making hydraulics more cost-effective in the long run.

Flexibility for a Wide Range of Applications

Lines of hydraulic presses are showing up in increasing numbers on high volume

jobs. The jobs listed below, and hundreds of others, are being done on hydraulic presses

today.

o Electric motor manufacturers assemble motor shafts to rotors, compress laminations,and press cores into housing.

o Automotive manufacturers press tiny shafts into water pumps, assemble shock

absorbers, blank and form diaphragms and stake disc brakes together.

o Jewelers coin Boy Scout pins.

o Frozen fish blocks are shaped for more efficient processing.


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o Aircraft companies form tough titanium housings.

o Tuba bells and cymbals are shaped in huge forming presses.

o Hardened road grader blades and machine ways are straightened.

o Hollowware manufacturers blank and draw brass bowls automatically from coiled

stock.

o Computer disc shafts are pressed into precision bearings.

In industries, hydraulics is commonly applied on presses. It has been widely used in

the said field. Here are ten advantages of using hydraulic presses.

1. Full power stroke

The full power of a hydraulic press can be delivered at any point in the stroke. Not

only at the very bottom, as is the case with mechanical presses. As an advantage, there areno allowances for reduced tonnage at the top of the stroke. In drawing operations, for

example, you have the full power of the press available at the top of the stroke. A person

doesnt have to buy a 200-ton press to get 100 tons throughout the stroke. Other advantages

are faster set-ups and no time consuming job of adjusting the stroke nut on the slide to

accommodate different dies.

2. Built-in overload protection

A 100-ton hydraulic press will exert only 100 tons of pressure (or less, if you have set

it for less) no matter what mistakes you make in set-up. You needn't worry about overloading

or breaking the press or smashing a die. When a hydraulic press reaches its set pressure

that is all the pressure there is. The relief valve opens at that limit and there is no danger of

overload.

3. Much lower original cost and operating costs

Hydraulic presses are relatively simple, and you may be surprised at the significant

cost advantage over mechanical presses in comparable sizes. The numbers of moving parts

are few, and these are fully lubricated in a flow of pressurized oil. Breakdowns, when theyoccur, are usually minor; not, for example, like a broken crankshaft. Replacements of

packing, solenoid coils, and occasionally a valve, are typical maintenance items. Not only are

these parts inexpensive, but also they are easily replaced without tearing the machine apart.

This means more up-time and lower maintenance costs.


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4. Larger capacities at lower cost

It is easier and less expensive to buy certain kinds of capacity in hydraulic presses.

Stroke lengths of 12, 18, and 24 inches are common. Extra stroke length is easy to provide.

Open gap (daylight), too, can be added without much additional cost. Similarly, larger table

areas and small presses with big bed areas can be provided. Large 200-ton presses withrelatively small beds are available; tonnage of the press doesn't dictate what the bed size will

be.

5. More control flexibility

Hydraulic press power is always under control. The ram force, the direction, the

speed, the release of force, the duration of pressure dwell, all can be adjusted to fit a

particular job. Jobs with light dies can be done with the pressure turned down. The ram can

be made to approach the work rapidly, and then shifted to a slower speed before contacting

the work. Tool life is thus prolonged. Timers, feeders, heaters, coolers, and a variety of

auxiliary functions can be brought into the sequence to suit the job. Hydraulic presses can do

far more than just go up and down, up and down.

6. Greater versatility

A single hydraulic press can do a wide variety of jobs within its tonnage range.

Commonly seen are deep draws, shell reductions, urethane bulging, forming, blank and

pierce, stake, punch, press fits, straightening, and assembly. They are also used for powered

metal forming, abrasive wheel forming, bonding, broaching, ball sizing, plastic and rubber

compression, and transfer molding.

7. Quiet

Fewer moving parts and the elimination of a flywheel reduce the overall noise level of

hydraulic presses compared to mechanical presses. Properly sized and properly mounted

pumping units meet and exceed current Federal standards for noise, even with the pump

under full pressure.

Because each phase of the ram movement can be controlled, noise levels can also

controlled. A hydraulic ram can be controlled to pass through the work slowly and quietly.

8. More compact

A typical 20-ton hydraulic press is eight feet high, six feet deep, and two feet wide. A

200-ton press is only ten feet high, nine feet deep, and a little over three feet wide. At ten


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times the capacity, the 200-ton press only takes up 50 percent more floor space. Hydraulic

presses become less and less expensive compared to mechanical presses.

9. Lower tool costsThe built-in overload protection goes for the tools, too. If they are built to withstand a

certain load, there is no danger of damaging them because of overloading. Tools can be

sized to withstand the load of a particular job, not a particular press. The pressure of the

press can be set down to suit the job. The lack of impact, shock, and vibration promotes

longer tool life.

10. Safety

No manufacturer will (or should) claim that hydraulic presses are safer than

mechanical presses. Both types of machines are designed and built to be safe if the controls

and safety features built in are used properly. Improperly used, all machines are potentially

dangerous. But the factor of control of the ram movements makes hydraulic presses easy to

make safe. Non-tie down, anti-repeat, dual palm button controls are used. The interlocking of

guards, as well as other safety devices, is relatively easy because of the nature of a

hydraulic press control system.

WEAKNESSES

Weaknesses of Hydraulic System

Expensive components and maintenance

o Intensive cleaning needed

o Conditioning and containing hydraulic fluid

Precision parts life are shortened due to exposure to bad climates and dirty

atmosphereo Hydraulic hose has a finite service life, which can be reduced by extreme

temperatures and no attention paid until failure occurs

o Clogging due to contaminants

o Any contamination in the internal fluid can cause clogs and jams, leading to

over pressurization or system failure.

8/7/2019 Hydraulics-final

Hydraulics-final na as in

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