FRL Unit.
Definition of FRL Unit:
In pneumatic system, the three elements combined in single compact unit in the sequence filter, regulator and Lubricator known as FRL unit.
● They are commonly fitted to each and every pneumatic work station. In certain cases, the filter and the regulator form a single unit referred as combination filter-regulator.
● It is the service unit for the compressed air. It is the combination of three units in a sequence as per their operation in the pneumatic system.
● The main three elements of FRL unit are :
1. Filter
2. Regulator
3. Lubricator
Construction:
● FRL unit is combined box set made up of a filter, regulator and lubricator with the associated fittings and wall mounting bracket used in Pneumatic system.
Importance of FRL unit:
● Air leaving a compressor is hot, dirty, and wet-which can damage and shorten the life of downstream equipment, such as valves and cylinders.
● Before air can be used it needs to be filtered, regulated and lubricated.
Function of FRL unit:
● Filter(F) : To remove the micron and sub-micron particles present in the entering air of compressor. It is used to separate out contaminants like dust, dirt particles from the compressed air.
● Regulator(R) : In pneumatic system the pressure of compressed air may not stable due to possibility of line fluctuation. Hence there is a need to maintain and regulate the air pressure. This function is performing by regulator.
● Lubricator(L): Sliding components like spool, 3 pneumatic cylinder has sliding motion between parts. It may cause friction and wear and tear at mating parts To reduce friction, lubricating oil particles are added in the compressed air with the help of lubricator.
Location of FRL Unit :
● It is located after outlet of compressor. The filter is installed upstream from other conditioning components. It protects the internal moving parts in the regulator from harmful contaminants and avoids fouling of the lubricator reservoir. Regulator is mounted after filter.
● Lubricators are installed at the downstream end of the FRL unit just after the regulator and should be placed as close to the equipment they serve.
1. Filter :
Definition : It is the device which separate out the impurities from the compressed air to supply clean and pure air to the system.
There are two types of filters given below :
(i) Air Filter (Filter in air line)
(ii) Coalescent filter
(i) Air Filter (Filter in air line):
Construction :
It consists of:
(a) Filter cartridge: It is the filter element made of sintered brass or bronze.
(b) Body : The body is the outer case with inlet and outlet passages.
(c) Plastic bowl : It is the cylindrical bowl fitted to the body at the upper ends while water drain valve is located at the bottom. It is transparent for easy visibility.
(d) Deflector and baffle : They are used to guide the flow of air from inlet to the outlet.
(e) Water drain valve : At the bottom of the plastic bowl, there is an on-off drain valve which could be manual operated to drain out accumulated water and other solid particles.
Working:
● When the air containing impurities enters in the filter through the inlet, it will allowed to strike on the deflector of the filter element.
● The thickness of the filter cartridge provides random zig-zag passage for the air to flow and arrest the solid particles in the cartridge passage.
● The water vapour gets condensed inside the filter and collects at the bottom of the filter bowl.
● Major part of the bigger foreign particles may also get separated from the air and collect at the bottom of the bowl.
● It is used to separate contaminants of size 15 to 25 mm (microns).
(ii) Coalescent filter:
● If oil molecules and moisture are to be separate out from the compressed air, then coalescent filter is used.
● The filter is made of metal-wool which is kept compressed inside a stainless steel shell and the outer shell is made of some porous material like ceramic or borosilicate.
● Porous material like borosilicate has the capacity to absorb the finer oil molecules. The filter medium is fitted on a seat made of stainless steel.
● It is used to filter out moisture and other impurities present in the air. The air enters at medium and porous material where oil and solid impurities are filter out. The clean and pure air is obtained from the outlet of the filter.
Function of the filter:
1. It is the first component of FRL unit. As name indicates, it is used to separate out contaminants like dust, dirt particles from the compressed air.
2. It gives clean, pure and contamination free compressed air to the pneumatic system.
3. The presence of contaminants may have bad effect on the finely finished mating surfaces of the pneumatic components.
4. Hence filter is the first component located after the compressor
Function of the filter removes moisture from air:
1.To prevent entrance of solid contaminants to the system.
2.To condense and remove the water vapour.
3.To arrest any submicron particles.
Pressure Regulator :
Definition: It is the device which regulates or controls the incoming pressure to the desired air pressure at a steady condition.
Function :
● Its function is to supply air at constant pressure regardless of variations in the flow and upstream pressure.
● It is useful in pneumatic system for :
(a) Supply of air at constant pressure regardless of flow variation or upstream pressure.
(b) Helps to operate the system more economically by minimising the amount of pressurised air that is wasted. This happens when system operates at pressure higher than needed for the job.
(c) Helps to promote safety by operating the actuator at reduced pressure.
(d) Extends component life because operating at higher than recommended pressure increases wear rate and reduces equipment life.
(e) Produces readily controlled variable air pressure where needed.
(f) Increases operating efficiency.
Construction :
The value has a:
1. Metallic body : It has two openings - primary and secondary.
2. Poppet valve : It is provided at the valve seat which helps for pressure regulation.
3. Diaphragm : It is the elastic member fitted at both the ends in a body of the valve. It is operated with the help of adjusting screw and spring.
4. Vent holes : They are provided for venting out compressed air if pressure increases above certain level.
5. Dampening spring : It helps to stabilise the pressure.
Working:
● The desired pressure is set with the help of adjusting screw. It will move the diaphragm in the upward direction.
● Thus, it will move the poppet from the valve seat and creates opening to allow air to flow from the primary side to the secondary side.
● The opening of the valve helps to regulate the pressure of air which depends on the compression of the spring by the setting screw.
● Pressure regulator acts as a pressure reducing valve and it ensures desired pressure level at various parts of the system.
● The two vent holes are used to exhaust air if secondary pressure to high level which is harmful to the system.
Types of pressure regulators:
(1) Non relieving pressure regulator
(2) Self relieving pressure regulator
(1) Non relieving pressure regulator :
Function:
● To regulate the pressure of compressed air with the help of unbalanced poppet by exhausting air through the application device (actuator / load).
Construction :
It consists of:
1. Poppet : It is the valve element which moves up and down to regulate the pressure of compressed air.
2. Diaphragm: It is the elastic member which is provided with spring on top side and poppet on bottom side.
3. Adjusting knob : It is the adjustment screw which helps to set the pressure of compressed air for the pneumatic application
4. Valve body : It is the outer case which holds all the components fitted properly with inlet and outlet ports.
Working:
This valve regulates the pressure of compressed air in following ways:
(a) When pressure of air is low :
When the inlet air pressure is less than the spring pressure, the force of the spring forces the poppet in the downward direction. The inlet port is directly connected to outlet port.
(b) When pressure of air is high :
The high pressure air forces the diaphragm in the upward direction and compress the spring, the poppet get lifted and reduces the air flow from inlet to the outlet. The air is vented through the Jod to maintain the pressure.
(ii) Self relieving pressure regulator :
Function:
When the air is vented through regulator itself to control pressure of compressor air, it is known as self relieving pressure regulator.
Construction and Working:
● It consists of adjusting screw, diaphragm and valve element fitted in the valve body. The inlet and outlet are given for air supply.
● The screw setting is adjusted so that it will push the valve in the downward direction and opens the valve openings to allow flow of air from inlet to outlet.
● When higher pressure is desired at the outlet, spring is compressed to higher value by adjusting screw which allows maximum opening of the valve to allow more air.
● If certain problem causes pressure at outlet to high value the air pass through orifice located at diaphragm and vented through vent holes to relieve excess pressure.
3. Lubricator:
Definition : It is the device which adds or mix particles of lubricating oil in the compressed air for the lubrication purpose, it is known as lubricator.
Principle :
● It works on the principle of venturimeter. The sketch shows the use of venturimeter principle for obtaining air and lubricating oil mixture.
● When compressed air passes through the venturimeter there is a pressure drop at the throat due to reduction is flow area.
● The throat is connected to the oil tank with the help of dip tube (oil pickup tube) which takes oil due to low pressure pushed at throat and by high pressure at the inlet A.
● The oil from the pickup tube will get mixed with the compressed air at the throat and further to the outlet of the venturimeter with the help of divergent cone.
● This mist of air and oil is supplied to the pneumatic system.
Construction:
It consists of:
1. Plastic bowl : It is transparent plastic bowl which contains sufficient quantity of lubricating oil. Usually servo spin 12 or shell - tellus 15 or SAE 10 grade oil is recommended.
2. Venturimeter : The venturimeter is fitted in the body of the lubricator with inlet for air and outlet for mixture of air and oil.
3. Oil pickup tube : Oil pickup tube is dipped at the throat section to take the oil from the bowl.
Working :
● The compressed air from the regulator is allowed to pass through the venturimeter. The air from the inlet of venturimeter is allowed to flow inside the bowl containing oil.
● As there is a drop in pressure at throat section, the oil pickup tube sucks the oil and it is feed to the oil drop tube.
● The oil drop tube collecting lubricating oil located at the sight feed dome allows fall of oil drops in the throat portion where they are mixed with air supply.
● The air with high velocity at throat brakes the oil particles and from mist of air and oil which flows out to the system.
Function of Lubricator (To add lubricating in the air) :
● In pneumatic system, components like sliding spool, pneumatic cylinders have sliding motion between parts. It may cause friction and wear and tear at mating surfaces.
● Hence to reduce friction, lubricating oil particles are added in the compressed air with the help of lubricator.
Dual (twin) pressure valve (AND Gate Valve)
● As name indicates, it is provided with twin (two) pressure inputs and a common output.
● This valve is very similar to the shuttle valve in shape and construction, but the function and the principle of operation is different.
● It is used for the logic AND connections. The picture and the symbol of the valve.
Construction and working :
●In pneumatic logic, a two pressure-valve works as an AND gate If a compressed air signal is applied to input P1 and input P2 at the same time, this will produce signal at output. However, if there is no signal, there is also no output signal.
● If only one input signal is applied, there will be no output signal.
● In case of time differences between the input signals the signal arriving last reaches the output.
● In case of pressure differences between signals, the signal with the lower pressure reaches the output.
Application :
● It is used in safety circuit when two operators are handling single machine like huge press machine in Which both the operators will place the large sheet of metal under then heavy punching ram and when both operators are safe then they will operate their valve push buttons to perform press operations.
Shuttle valve (OR gate Valve)
It is the valve which allows air supply through either port 1 or port 2 with the help of control element, which moves like a shuttle in the valve passage.
Need or purpose:
● Certain pneumatic systems, the supply of compressed air to a subsystem must be from more than one source to meet system requirements.
● In some systems an emergency system is provided as a source of pressure in the event of normal system failure.
● The main purpose of the shuttle valve is to accept the pneumatic signals from two different locations.
Construction:
● It is also known as OR GATE valve. It has three ports:
(a) P1 and P2 → inlet ports
(b) Outlet port
● The control element is the ball which is placed in the passage of port P1 and port P2.
Working:
(a) P1→ outlet, P2 → closed:
● When an air supply is allowed to enter in the port P1, it moves the ball and closes the port P2. The air will flow from port P1 to the outlet.
(b) P2 → outlet, P1 → closed:
● When an air supply is allowed to enter through port P2, it moves the ball and closes the port P1. The air will flow from port P2 to the outlet.
●Hence it will supply air through either port P1 or port P2
Applications:
● The supply of compressed air to a subsystem must be from more than one source to meet system requirements.
● In some systems an emergency system is provided as a source of pressure in the event of normal system.
Quick Exhaust Valve:
● When air is exhausted from the cylinder without passing in the D.C. valve and exhausted quickly through the valve known as quick exhaust valve.
● It helps to induce higher speed in a cylinder through quick exhaust of air.
Construction and working :
● During the movement of cylinder, air from the cylinder will exhaust through port A to port R to the atmosphere without travelling through port P and thus quick exhaust occurs.
● A quick exhaust valve is a typical shuttle valve. It consist of a movable disc (also called flexible ring) and three ports namely, Supply port P, which is connected to the output of the final control element (Directional control valve). The Output port, A of this valve is directly fitted on to the working port of cylinder. The exhaust port, R is left open to the atmosphere
● Forward Motion: During forward movement of piston, compressed air is directly admitted behind the piston through ports P and A, Port R is closed due to the supply pressure acting on the diaphragm. Port R is usually provided with a silencer to minimize the noise due to exhaust.
● Return Motion : During return movement of piston, exhaust air from cylinder is directly exhausted atmosphere through opening R (usually larger fitted with silencer). Port P is sealed by the diaphragm. Thus exhaust air is not required to pass through loan and narrow passages in the working line and final control valve.
Application of a Quick exhaust Valve:
They are available in a variety of shapes and sizes and are used in the industry to speed up the performance of a moving cylinder, evacuate air directly out into the atmosphere and increase the cylinder rod reaction time, or valve actuator.
Time Delay Valve
● As name indicates, this valve is used to initiate a delayed signal in the pneumatic system.
● It is useful in sequencing circuits to actuate the cylinder or motor with certain time delay.
Construction:
● This valve has three main components:
a) In built air reservoir (air chamber)
b) In built non return valve
c) Pilot controlled spring return 3/2 D.C. valve.
Working:
● Initially when compressed air is supplied to the port P of the valve, it is prevented from flowing to port A from port P, as the spool blocks this port A.
● When air is allowed to enter through pilot port Z, it flow through needle operated flow control valve where its flow can be regulated.
● The air then enters in the air chamber where pressure starts building here. when sufficient amount of pressure is generated, it pushes the spool of 3/2 D.C. valve.
● Now the opening port P is get connected port A and port R is closed. Air can flow easily from port P to port A to actuate the actuator.
● The time required to build up the pressure in the reservoir is the amount of time delay of the time delay valve.
● The time delay can be set by using needle adjustment screw to control flow rate of air.
● In pneumatic time delay valve, typical time delays in the range 5-30 seconds are possible. The time delay can be extended with the addition of external reservoir.
