The difference between self operated valve and command device

- Nov 15, 2018-

Self-operated control valve, also known as self-operated control valve, relies on the pressure and temperature of the medium flowing through the valve itself as energy source, uses the feedback signal (pressure, differential pressure, temperature) from the output end of the valve to transmit to the actuator through the signal tube, drives the valve disc to change the opening of the valve, so as to achieve the purpose of regulating pressure, flow and temperature. Yes.

1. Direct acting self regulating valve:

Also known as spring-loaded regulating valve, diaphragm up and down, or the comparison of the pressure behind the valve and spring force, or the comparison of the pressure before and after the valve to control the opening of the valve, its structure has elastic components: such as spring, bellows, bellows, thermostats, etc., using the principle of elastic force and feedback signal balance.

2. Self regulating valve with command device:

It adds a commander (pilot valve) to amplify the feedback signal and then drives the movement of the main valve disc through the actuator to change the opening of the valve. If it is a pressure regulating valve, the feedback signal is the outlet pressure of the valve, which is introduced into the actuator through the signal tube; if it is a flow regulating valve, there is an orifice plate (or other resistance devices) at the outlet of the valve, which takes out the differential pressure signal from both ends of the orifice plate and introduces it into the actuator; if it is a temperature regulating valve, the outlet of the valve has temperature. The degree sensor (or Wen Bao) drives the actuating mechanism through the thermal expansion and contraction of the medium in the temperature sensor.

Generally speaking, the control accuracy of the direct acting self-operated valve is not high. The main purpose of increasing the commander is to increase the control accuracy. It can be about twice as high as that of the general direct operating self-operated valve and has a large pressure difference ratio (such as 0.8MPa in front of the valve and 0.001MPa behind the valve). It is especially suitable for micro-pressure gas control.