Main components and structure of pneumatic control valve

Pneumatic control valve uses compressed gas as the power source, cylinder as the actuator, and uses valve positioner, converter, solenoid valve, position-holding valve, gas storage tank, gas filter and other accessories to drive the valve, realize switch quantity or proportional regulation, and receive the control signal of industrial automation control system to complete the regulation of pipeline medium: flow, pressure, temperature, liquid level and other process parameters. The characteristics of pneumatic control valve are simple control, fast response, and inherent safety, without the need for additional explosion-proof measures.

Main components of pneumatic control valve

The pneumatic control valve is a control valve product with simple control, quick response and intrinsic safety. It plays an indispensable role in the field of industrial automation control. This article mainly talks about the main components of the pneumatic control valve.

1. Pressure reducing valve: reduce the control gas source pressure to suit the working pressure of the actuator;

2. Filter: Filter out water and other impurities in the compressed air to ensure the cleanliness of the compressed air entering the electric/pneumatic converter positioner and the actuator. Many products are integrated designs of pressure reducing valves and filters.

3. Electric/pneumatic converter: converts the 4-20mA current signal of the control system into a 3-15psi (0.2-1kg/cm2) air pressure control signal;

4. Positioner: It is the core component of valve position control and accurately controls the valve position of the regulating valve;

5. Position transmitter: The displacement of the connecting rod and the valve stem synchronously generates angular movement, which is converted into a 4-20mA electrical signal, linearly reflecting the opening of the valve.

6. Travel switch: Usually installed in the fully open and fully closed positions of the valve to send valve fully open and fully closed signals to the control system.

7. In order to realize some special control functions, some actuators are also equipped with other control components, such as solenoid valves for interlocking functions, holding valves for holding functions, pneumatic amplifiers to speed up the action speed, and energy storage tanks to maintain short-term operation in the event of air loss.

Pneumatic control valve structure:

The pneumatic control valve is mainly composed of three parts: pneumatic actuator, valve body and accessories. The actuator is powered by clean compressed air, receives 4~20 mA electrical signals or 20~100KPa gas signals, drives the valve body to move, changes the flow area between the valve core and the valve seat, and thus achieves the function of regulating the flow. In order to improve the linearity of the valve, overcome the influence caused by the friction of the valve stem and the changes in the working conditions (temperature, pressure) of the regulated medium, a valve positioner is used in conjunction with the control valve, so that the valve position can be accurately positioned according to the regulation signal.

The actuator is composed of the diaphragm/piston, spring, handwheel, pneumatic rod, coupling and other main components; the main components of the valve body are valve cage, valve disc, valve seat, valve stem, valve cage pressure ring, etc.; other accessories include solenoid valve, pressure reducing valve, filter, current/air pressure converter, positioner, flow amplifier, etc.

In order to ensure the safe operation of the unit, some important valve designs are equipped with accessories such as solenoid valves, position-holding valves, and quick pressure relief valves to ensure that the regulating valves can quickly open (close) or perform protection functions (three-break self-locking protection functions) in the event of power failure, signal loss, or gas loss, thus meeting the safe operation requirements of the process system.

The control valve has three protections: air source off protection, power source off protection and signal source off protection.

principle:

Pneumatic control valves are usually composed of pneumatic actuators and control valves connected, installed and debugged. Pneumatic actuators can be divided into single-acting and double-acting types. Single-acting actuators have return springs, while double-acting actuators do not have return springs. Single-acting actuators can automatically return to the open or closed state initially set by the valve when the source is lost or a sudden failure occurs.