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 Page 1 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
Instrumentation : Document No. 10 Page 2 of 20
Created : 01 February 2003 Revision No: 01Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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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.
Instrumentation : Document No. 10 Page 3 of 20
Created : 01 February 2003 Revision No: 01Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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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.
Instrumentation : Document No. 10 Page 4 of 20
Created : 01 February 2003 Revision No: 01Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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Instrumentation : Document No. 10 Page 5 of 20
Created : 01 February 2003 Revision No: 01Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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AIR REGULATORS, FILTERS AND LUBRICATORS
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
Instrumentation : Document No. 10 Page 6 of 20
Created : 01 February 2003 Revision No: 01Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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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
Instrumentation : Document No. 10 Page 7 of 20
Created : 01 February 2003 Revision No: 01Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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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
Instrumentation : Document No. 10 Page 8 of 20
Created : 01 February 2003 Revision No: 01Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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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 Page 9 of 20
Created : 01 February 2003 Revision No: 01Last Approved : March 2003 First Published : March 2003
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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 Page 10 of 20
Created : 01 February 2003 Revision No: 01Last Approved : March 2003 First Published : March 2003
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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)
Instrumentation : Document No. 10 Page 11 of 20
Created : 01 February 2003 Revision No: 01Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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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.
Instrumentation : Document No. 10 Page 12 of 20
Created : 01 February 2003 Revision No: 01Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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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.
Instrumentation : Document No. 10 Page 13 of 20
Created : 01 February 2003 Revision No: 01Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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MODULE – RFL
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?
__________________________________________________________________
__________________________________________________________________
____________________________________________________________
Instrumentation : Document No. 10 Page 14 of 20
Created : 01 February 2003 Revision No: 01Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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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
Instrumentation : Document No. 10 Page 15 of 20
Created : 01 February 2003 Revision No: 01Last Approved : March 2003 First Published : March 2003
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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)
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
Instrumentation : Document No. 10 Page 16 of 20
Created : 01 February 2003 Revision No: 01Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
______________________________________
Instrumentation : Document No. 10 Page 17 of 20
Created : 01 February 2003 Revision No: 01Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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RFL
AIR REGULATORS, FILTERS AND LUBRICATORS
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.
Instrumentation : Document No. 10 Page 18 of 20
Created : 01 February 2003 Revision No: 01Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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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
Instrumentation : Document No. 10 Page 19 of 20
Created : 01 February 2003 Revision No: 01Last Approved : March 2003 First Published : March 2003
Revised : Owner: Learnership Dept.
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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.
Instrumentation : Document No. 10 Page 20 of 20
Created : 01 February 2003 Revision No: 01Last Approved : March 2003 First Published : March 2003