Module - Rfl

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MODULE - RFL

MODULE – RFL

AIR REGULATORS, FILTERS AND LUBRICATORS

INTRODUCTION

Industrial plants use a power system of one type or another. Work may be done

by a substance under pressure. This substance can either be a gas, e.g.

Compressed air, or a liquid, e.g. oil.

A system that uses a gas for transmitting force, is called a “Pneumatic” system.

Pneumatic systems are often used in the mining industry, e.g. in rock drills and

mechanical loaders that are used underground. Pneumatic systems are also used

in Process Instrumentation Control Systems that are to be found in plants on

surface or underground.

The air filter, regulator and inline lubricator are connected in line between the “air

supply system” and the instrumentation that uses air to operate. These devices

are used to regulate and enhance the quality of the air supplied to the instrument.

NOTE: The lubricator is only used when air is supplied to a device that requireslubrication, for example, air cylinders, air motors and some solenoid valves. In

such cases, the unit is installed just before those units.

When working with Pneumatics, there are two factors to consider. Namely

pressure and flow. This module will describe these factors. This module will

describe these factors. This module will also introduce you to the devises that are

used to provide a stable high quality air supply system.

PRESSURE

Pressure is defined as force per area. The basic unit of pressure measurement is

called the Pascal (Pa). There are 1000P in one kPa and 100kPa in 1 bar. The unit

Instrumentation : Document No. 10 of 20

Created : 01 February 2003 Revision No: 01Last Approved : March 2003 First Published : March 2003

Revised : Owner: Learnership Dept.



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kPa is used in pneumatics and hydraulics, because it is the most practical unit for

these types of applications.

If you blow up a balloon, you have created pressure. See the following figure.

FIGURE – 1

FLOW

Flow is the volume of air moved through a system in a certain period of time.

(figure – 2) Flow is expressed in terms of meter per second (m/s), cubic meter pet

minute (m²/min), or liters per second (l/s).

Figure – 2






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Flow and pressure are related, but they are obviously not the same. Pressure

difference can cause flow. If you let the air out of the balloon, you have caused the

air to flow. See figure – 3.

FIGURE – 3

It is possible to have a high pressure difference and relatively low flow. In figure –

4 a cylinder is filled very slowly through a small pipe at a high pressure. The piston

will move very slowly, but it will be able to lift a very heavy load due to the high

pressure.

Figure – 4

Conversely, you can have a high flow pressure difference. In figure – 5, a

compressor is supplying a large volume of air at a very low pressure to a cylinder.

You could stop this piston with one finger, but if the load is small it will travel at a

very high speed.






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Figure – 5

You can see from the examples given that:

a) PRESSURE causes the FORCE that permits the actuator to perform

mechanical work.

b) FLOW causes the SPEED at witch the actuator will perform work.

NOTE:

When a system is subject to a certain pressure, it is important to remember that

there is an equal force acting on every surface of that system. In figure – 6 a

force of 10 Newton (N) is acting in all directions and in all directions on all

surfaces.






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SELF TEST – 1

QUESTION – 1

What are the two main factors to consider in pneumatic systems and what are

their units of measurement?

a) _______________________in________________________________

b) _______________________in________________________________

QUESTION – 2

What causes the force in a actuator?

______________________________________________________________

QUESTION – 3

What causes the speed at wich the actuator moves?

______________________________________________________________

LEARNER

TRAINIG OFFICER

DATE.

AIR FILTERS






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FIGURE – 7

An air filter is normally installed before each instrument air user, in order to remove

the contaminants which otherwise would reduce the life span of instruments, clog

the small orifices and in general cause malfunctions.

Most inline air filters are of the stage mechanical separation type. The air entering

the unit is deflected into a swirling path, this causes the centrifugal force to cause

the larger particles and droplets to collect on the wall of the bowl.

A baffle plate in the lower part of the filter reverses the direction of the airflow

providing a quiet zone for the separated solids and liquids.

After this cyclonic separation, the air flows through the filter element which

removes the finer particles (see figure – 7). Filter bowls are normally made from a

transparent polycarbonate plastic, which allows for visual inspection of the filter

element and the amount of material collected in the bowl, without disassembling

the unit. The plastic bowls normally have protective guards around them to protect






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them against mechanical damage, but for full protection from mechanical damage,

a metal bowl should be used.

In most designs, the filtering element needs only to be cleaned, not replaced and

therefore the units are available with a quick release collar, which makes servicing

much more convenient. A manually operated stop cock at the bottom of the bowl

is used for draining collected material from the bowl. Units are also available with

automatic drains that are triggered by a float mechanism. As the liquid in the bowl

rises, the float lifts the drain valve, which in turn opens the drain. As the liquid

drains, the float descends to close the drain valve. Because the liquid is not

allowed to drain completely, no loss of compressed air occurs during this

procedure.

Air filters should be sized according to the airflow demand required by the

instrument. Oversize filters may not cause enough swirling action to separate all of

the droplets. Undersize filters require excessive operating pressure drops and

may create too much turbulence in the air to permit the particles and liquid to

settle.

Filters should be installed upstream and as close as possible to the instruments

they serve. The filter should be mounted in such a way that the bowl is installed in

a vertical position and in such a way that it is easy to observe the bowl for

inspection and draining purposes. Filters must never be opened or disassembled

whilst under pressure. Always ensure that the device has been properly isolated

and depressurized before performing any maintenance on the device.

AIR LUBRICATORS

Air lubricators (figure – 8) can either be installed directly in the air supply line, or

mounted remotely. For the in-line lubricator the flowing air lifts the oil from the

reservoir or bowl and injects it into the air steam and occasionally drop out and






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collect on the tube walls. By means of the sweeping action of the air and also

gravity, the air is moved along the airline to the cylinder.

For an air motor or oil tool, the air flow is unidirectional (figure – 8a) and for a dual

acting cylinder, air flow reversals occur frequently. (figure – 8b). For both of these

installations, an inline lubricator is recommended, but for the bi-directional

application, the lubricator should be installed upstream of the diverting valve.

In the inline lubricators, the oil delivery rate can be measured by a sight ball in a

graduated pickup tube or by a drip chamber where each drop of lubricant isobserved as it enters the air stream.

LUBRICATOR INSTALLATIONInstrumentation : Document No. 10 of 20





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If a filter, regulator and lubricator are required, the lubricator should be installed

downstream from the other devices. (See figure – 9)

FIGURE- 9

Combination units are available that incorporate a filter, regulator and lubricator

into a single unit. Lubricators with integral reservoirs should be mounted in the

vertical position and located in such a way that they can easily be accessed for

inspection and refilling, without exposing them to mechanical damage. The

lubricator bowl can be equipped with guard protectors that are perforated so as to

allow for visual inspection of the lubricant level.

Air lubricators should be installed at the same height or higher than the units that

they are serving. At startup, the lubricated air lines should be recoated with

lubricant in order to eliminate the lag time that it would take for the first lubricant to

reach the destination.

Oil delivery rate should be checked and readjusted as required to meet the

variable air flow conditions. The exact amount of lubricant to each user is not

critical, as long as there is sufficient lubricant reaching the cylinder.

PRESSURE REGULATORInstrumentation : Document No. 10 of 20





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The pressure regulator is used to reduce the pressure, being supplied from the

compressor, to a constant pressure that is required by each individual instrument.

If the supply to an instrument is not kept constant, it would not be able to give the

correct information to control the process accurately.

FIGURE – 10

With reference to figure – 10, the pressure required by the instrument is set by

adjusting the main range spring (A), acting downward on the diaphragm (C). This

will push the diaphragm and main valve assembly (H) downward, thus opening the

supply valve (E). This will allow air to pass from inlet (F) to the outlet (G). Air

passing the aspirator tube creates a lower pressure in the control chamber,

causing the supply valve to open further. (Figure – 11)






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FIGURE – 11

As the pressure in the outlet builds up, it will also build up in the control chamber

via the aspirator tube (B). As soon as the pressure builds in the control chamber

starts building up, the diaphragm will start lifting, which will tend to close the supply

valve and open the vent valve, until the spring force is balanced. As long as the

pressure in the outlet remains constant, a balance will be maintained between the

supply valve and the vent valve. If the flow of air to the instrument is stopped, thepressure at the outlet will increase above the value, causing the diaphragm to be

lifted. This will close the supply valve and open the vent valve, which will cause a

reverse flow, venting the excess pressure as shown in figure – 12.






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FIGURE – 12

When the outlet pressure has again reached the required value, a balance is again

setup between the supply valve and the vent valve.

Note that figure – 10 shows a fixed pressure regulator, where the force of the

range spring is adjusted by the bolt and then locked in position with the nut.

Regulators are also available with a hand wheel to facilitate easy adjustment.

Examples of such regulators are to be found on the calibration panels in the

workshop. If you have any questions, ask your Training Officer.






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AIR REGULATORS, FILTERS AND LUBRICATORS.

SELF TEST – 2

QUESTION – 1

Label the diagram of the typical air filters supplied below. (Include air flow).

QUESTION – 2

Where is an air filter installed with respect to an instrument?

__________________________________________________________________

__________________________________________________________________

____________________________________________________________






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QUESTION – 3

With respect to what is an air filter sized?

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________

QUESTION – 4

How is the oil dispersed in or from an inline air lubricator?

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________ ______________________________________________

QUESTION – 5

How is the oil delivery measured in an inline air lubricator?

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________

QUESTION – 6






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With respect to an air filter and regulator, where is an inline air lubricator installed?

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________

QUESTION – 7

Label the components on the diagram below.

QUESTION – 8

Describe how the air regulator operates. (Refer to the diagram in question – 7)

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________






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__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

______________________________________






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CRITERION TEST

Learner

Learner signature

Agreement number

Assessor signature

Date

Result Competent / Not yet competent

QUESTION – 1

What are the two main factors to consider in pneumatic systems and what are their

units of measurement?

a)____________________________in_________________________________

b)____________________________in_________________________________

QUESTION – 2

What causes the force in an actuator?

________________________________________________________________

QUESTION – 3

What causes the speed at which the actuator moves?

________________________________________________________________

QUESTION – 4

Label the diagram of the typical air filter supplied below.






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QUESTION – 5Where is an air filter installed with respect to an instrument?

__________________________________________________________________

__________________________________________________________________

____________________________________________________________

QUESTION – 6

With respect to what is an air filter sized?

__________________________________________________________________

__________________________________________________________________

____________________________________________________________

QUESTION – 7






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How is the oil delivery measured in an inline air lubricator?

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________

QUESTION – 8

With respect to an air filter and regulator, where is an inline air lubricator installed?

__________________________________________________________________

__________________________________________________________________

____________________________________________________________

QUESTION – 9

Label the components on the diagram below.



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