Introduction to main accessories of pneumatic actuator
Main accessories of pneumatic actuator
1、 Filter pressure reducing valve
Filter pressure reducing valve is an accessory of industrial automation instrument. Its main function is to filter and purify the compressed air from the air compressor and stabilize the pressure at the required value. It can be used as the air supply source and pressure stabilizing device for various pneumatic instruments, solenoid valves, cylinders, spraying equipment and small pneumatic tools.
Filter pressure reducing valve can be divided into:
A. Duplex (filter, pressure reducing valve)
Function: filter and decompress compressed instrument air
B. Triple piece (optional filter, pressure reducing valve, oil atomizer, pressure gauge)
Function: filter and decompress the compressed instrument air, and lubricate the air.
be careful:
It is easy for some people to confuse the air supply triplet with the pneumatic triplet. The difference between the two is that the air source triplet is composed of three parts: filter, pressure reducing valve and oil atomizer. The pneumatic triplet is composed of three parts: air source triplet, signal switch and solenoid valve. The air source triplet is a part of the pneumatic triplet.
The filter is a purifying device for air. It filters out water and impurities in the air and is an integral part of the pneumatic actuator. Otherwise, absorbing impurities will affect its use function and service life. The pressure reducing valve regulates the pressure of the air source to a constant pressure. After the pressure reducing valve regulates the pressure appropriately, a locking device is used. The function of the oil atomizer is to send oil to the cylinder through the air pipe to lubricate the cylinder.
2、 Solenoid valve
Definition: A valve that uses an electromagnet to control the movement of the valve core is generally opened and closed by controlling the movement of the pneumatic actuator.
The on-off valve is a commonly used solenoid valve, which controls the air source, air circuit switch and valve switch through voltage signal.
Classification of solenoid valve:
1. Classification according to operation mode
Manual operation: button type, handle type, pedal type;
Mechanical operation: plunger type, roller lever type;
Pneumatic operation: direct control, brief control;
Electrical operation: direct acting, pilot operated.
2. Pneumatic actuators are classified according to usage
It is divided into two solenoid valves, two three-way solenoid valves, two four-way solenoid valves, two five way solenoid valves and three five way solenoid valves.
3、 Limit switch
Limit switch, also known as travel switch, is an electrical switch that indicates and feeds back the limit position of mechanical equipment movement.
The limit switch is divided into ordinary limit switch and explosion-proof limit switch; With inductive switch Contact type. Travel switch; Plastic limit switch Aluminum alloy limit switch. Stainless steel limit switch; The specification of limit switch is 210.310.410.510, etc; Protection level of limit switch: limit switch IP65.IP67.IP68, etc; Common limit switch and low temperature limit switch; In addition, there is an explosion-proof grade.
4、 Positioner
The valve positioner is the main accessory of the control valve. It takes the valve stem displacement signal as the input feedback measurement signal and the controller output signal as the setting signal for comparison. When there is a deviation between the two, the output signal is changed to the actuator to make the actuator move and establish a corresponding relationship between the valve stem displacement times and the controller output signal.
1. Classification of valve positioner
(1) According to the structure and working principle, the valve positioner is divided into:
a. Pneumatic valve positioner: the input signal is the standard gas signal. For example, the output signal of 20~100kPa gas signal is also a standard gas signal.
b. Electric valve positioner: the input signal is a standard current or voltage signal. For example, the 4~20mA output signal is the current signal of the standard gas signal.
c. Intelligent valve positioner
(2) Whether the valve positioner has CPU can be divided into: ordinary electric valve positioner and intelligent electric valve positioner.
2. Positioner
(1) When the medium pressure is high and the pressure difference is large;
(2) When the diameter of regulating valve is large (DN>100);
(3) High temperature or low temperature control valve;
(4) When it is necessary to increase the action speed of the regulating valve;
(5) Use standard signal to operate non-standard spring actuator (beyond the range of 20~100KPa spring);
(6) When used for split range control;
(7) Reverse the movement of the valve (air to close and air to open switch each other);
(8) Need to change the flow characteristics of the valve (the positioner cam can be changed);
(9) When there is no spring actuator or piston actuator to achieve proportional action;
(10) When the pneumatic actuator is operated by electric signal, the power distribution air valve positioner must be used.
3. Function of positioner
(1) An important regulating system used to improve the positioning accuracy and reliability of the regulating valve.
(2) It is used in the case of large pressure difference at both ends of the valve. In order to overcome the imbalance between the liquid and the valve core, reduce the stroke error, increase the air source pressure and increase the output force of the actuator.
(3) When the regulating medium is high temperature, high pressure, low temperature, toxic, flammable and explosive, in order to prevent external leakage, the packing is often compressed, the friction between the valve stem and the packing is large, and the positioner can overcome the lag.
(4) When the regulated medium is viscous fluid or contains suspended solids, the use of a positioner can overcome the resistance of the medium to the movement of the valve stem.
(5) In order to increase the output thrust of the actuator, the regulating valve is used for large diameter (Dg>100mm).
(6) The distance between the regulator and the actuator is 60m, which can overcome the delay of control signal transmission and improve the reaction speed of the valve.
(7) Used to improve the flow characteristics of the regulating valve.
5、 Pneumatic control valve
6、 Quick exhaust valve
Structure of quick exhaust valve
7、 Retaining valve
The pneumatic lock valve, also known as the pneumatic lock valve, is an auxiliary component of the pneumatic unit combination instrument. When the air source system fails, the holding valve can automatically cut off the channel between the regulating instrument and the regulating valve, so that the opening of the regulating valve can be guaranteed to stop before the failure and the process can operate normally. After eliminating the air source fault, it can automatically resume normal operation. Therefore, the safety valve can be used as a safety protection device in the automatic control circuit.
Function: In case of loss of air or power in the control circuit, the position keeping flash valve can be used to keep the valve in position before failure.
8、 Pressure switch
The air supply pressure of the high pressure control actuator passes through the pressure switch to ensure that the actuator can obtain a stable output torque.
9、 Governor valve
One way speed regulating valve: the opening and closing speed of the valve is controlled by regulating the air volume input to the actuator. Generally, exhaust throttling is adopted, which is more stable and reliable.
10、 Manual operating mechanism of pneumatic actuator
Classification: mechanical handwheel, gear box, manual hydraulic pump device.
Function: It is used to open and close the valve when the circuit and gas circuit are cut off or there is a fault.
