4.1 AIR CONTROL 4.1.1 Fluid Conditioner FRL unit consist of Filterations, Regulators and Lubricator unit. It is also known as Air Service Unit. Primary function is to provide clean air at optimal pressure and occasionally adds lubrication to extent the life of the pneumatic system components which need lubrication. Figure 4.4 : FRL Unit
Air Filter Filters all dust, rust, and condensed moisture in the compressed air. All dust, moisture are trapped in a storage underneath and must be emptied regularly
Regulator To ensure a steady (stable) air pressure in the system
Lubricator Supplies a mist of lubrication oil to the system in a controlled manner. The oil is used for lubrication of mechanical component Lubrication is need; a) the actuator is working under continuous reciprocating operation b) using large pneumatic cylinder
Air Service Unit Also known as FRL unit and symbol with lubrication without lubrication
4.1.2 Air Control Valve a) Directional Control Valve (DCV) A valve is a device which receives an external command. The command can either be in the form of mechanical, fluid pilot signal or electrical. This command is used either to release, stop or redirect the fluid that flows through it.
A control mechanism is needed to control air flow direction, in and out the cylinder for its operation. It is known as directional control valve (DCV)
Basic Valve Symbols Valve symbols is build from the following basic symbols; position Number of switching position Air flow lines, the arrow show air flow direction Shut off position
Ports and Positions for Control valve
Directional Control Valve Symbols
Valve Actuation Valve need some kind of mechanism to switch one position to another. Among the actuation mechanism are as follows;
Type of Actuation Symbols
Manual Actuated Mechanical Actuated
Pressure Actuated Solenoid Actuated
Example 1: 3/2 Way Valve There is a standard way to marking each port of the valve ( according ISO 11727) 1- compressed air supply 2- connection to cylinder 3- exhaust port The control valve usually drawn at its normal position ( before operation)
Example 2: 5/3 Way Valve 1- compressed air supply 2 & 4 - connection to cylinder 3 & 5- exhaust port The control valve usually drawn at its normal position ( before operation)
Pressure Actuated Solenoid Actuated Solenoid valves convert electrical energy into pneumatic energy. It can also used DC or AC supply. The advantages to used solenoid valve is that, electrical signal are very fast and efficient in actuating movement.
DCV Design There are two types of construction that is spool/sleeve/slide and popet. Recently spool valve is the most frequently used. Spool Valve Spool valve may be built for more than two switching position with normally spring centered. The valve is also balanced and uses only small actuating forces. Spool valve may operate without elastomer seals because the tolerance is very small. Figure 4.10 Spool Valve
Popet Valve Although spool valve is favourable in modern design, popet valve also offer significant advantage. Popet valve do not required lubrication and no close tolerance gaps on moving parts since they provide head-on instead of dynamic sealing. Popet valve also requires much higher operating force.
b) Pressure Control Valve The function of pressure control valve is to influence the pressure of the compressed air or react to specific values of pressure. The most commonly term used for pressure reducing valve is pressure regulator. Pressure reducing valve is used to maintain a nearly constant secondary pressure (adjusted pressure) and independent of pressure fluctuation on the primary side.
Pressure Reducing Valve
c) Ancillary Valves i) Check valves The function of check valve is allow airflow from one direction only. The opposite airflow will be cut off. It will also prevent backflow in diverse applications. To control this, check valve is equipped with or without spring with popet.
ii) Shuttle Valve Shuttle valve is also known as OR valve where it will only allow flow in only one direction at a time. The flow is cut off by sealing body that are made in the form of ball, cone or disc seal.
iii) AND Valve Double Cut-Off Valve normally is called as AND valve. Means that both inpu must be pressurized to obtain an output signal.
iv) Quick Exhaust Valve Quick exhaust valve is used as a speed controlling device. It allow the air to flow from the power port (Port P) to the actuator to which it is attached (Port A). When the actuator is exhausting, the valve element is shuttle to the left where it blocks port P and the exhaust air can rapidly flow through a large exhaust port (R) to atmosphere.
4.2 ACTUATOR (PNEUMATIC DRIVE ) Pneumatic drives convert the energy of pressure into mechanical work (pressure and flow into force and velocity). The work done by pneumatic actuators can be linear or rotary Linear movement is obtained by piston cylinder. Reciprocating rotary motion with an angle up to 270 O can be obtained by vane or rack and pinion type actuation. Pneumatic drive is devided into four category such as:- Linear Cylinder Rotary Cylinder Special Cylinder Compressed Air Motors However, it is necessary to have knowledge of basic construction on pneumatic cylinder when dealing with it. Figure 4.18 illustrates the main component of pneumatic cylinder.
Main Component of Double Acting Cylinder
Common Mounting for Pneumatic Cylinder
a) LINEAR CYLINDER Linear cylinder is is a very common cylinder used in pneumatic system. T wo types of linear cylinder is Single Acting Cylinder (Figure 4.18) and Double Acting Cylinder (Figure 4.19) Single acting cylinder is used whenever the force is needed in one direction only and where the return stroke is unimpeded and unloaded. Double acting cylinder is used whenever linear motion with small and medium forces is required and work is to be performed in both directions. Single Acting Cylinder-Spring Retract Type Double Acting Cylinder
b) ROTARY CYLINDER Rotary cylinder is used to transform the linear motion of a double acting cylinder into rotary motion. The angle of the rotation is also limited. Standard angle of rotation is commonly 90 O or 180 O. Figure 4.20 illustrates Rotary Actuators. Rotary Actuators
c) SPECIAL CYLINDER Double Acting Cylinder with Double Piston Rod This cylinder can perform work at both sides. The guidance of the piston is improved by the used of bearing.
Rodless cylinders Rodless Cylinder with Mechanical Connections Rodless Cylinder with Magnetic Force Rodless cylinders differ from basic air cylinders in that no piston rod extends outside the cylinder body. Instead, the internal piston is connected to an external carriage, by means of a magnetic or mechanical coupling system.
Multi Position Cylinder Multiposition Cylinder is used to attained number of stable position where two or more cylinder are combine. Normally it is used for sorting operations, movement of flaps.
Telescopic cylinder Telescopic cylinder is design for long strokes. It can also holds large forces and consists of several nested cylinder.
Tandem Cylinder Tandem cylinder is built with self lubrication element. It consists of two double acting mechanically coupled cylinder. Specially design for large forces and small strokes. Normally used for special machines where the diameter is limited by the space available.
Fine Lock Cylinder For this kind of cylinder, mechanical brake is used to stop the cylinder at stable intermediate position. It can hold forces higher than the maximum pneumatic force.
CUSHIONING CYLINDER Cushioning is an important element in pneumatic cylinder. In order to achieve smooth braking and noise reduction, internal and external cushioning methods can be used. The cushioning is achieved by the built up of pressure in the chamber sealed by the cushioning piston. Figure below illustrates the cushioning mechanism for pneumatic cylinder. Pneumatic Cylinder End Cushioning
Pneumatic Drive Symbols
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