Self-acting control valve

Stabilizes pressure; principle can be found on Baidu

This post was last edited by ylb913 on 2015-12-29 06:50. It serves the same purpose as a control valve operated by DCS in indoor applications, namely to control the pressure behind the valve. It’s just controlled on-site directly, without using a DCS. A self-acting control valve is a type of valve that requires no external power source; it utilizes the pressure changes of the medium being regulated to carry out automatic adjustment. Based on mechanical principles, it directs the controlled medium into an actuator to generate force that drives the valve core element up and down, thereby achieving automatic regulation and stabilizing the pressure behind the valve – making it an energy-saving product. The functional principle of a self-acting control valve is the same as that of a conventional control valve; the main difference is that it does not require external power and does not accept control signals from external instruments. The biggest advantage of this product is its ability to operate in environments without electricity or gas, with the pressure setting able to be adjusted at will during operation. The main difference between a self-acting control valve and a pressure reducing valve: 1. Their functions are different; the self-acting control valve is designed for regulation, while the pressure reducing valve serves solely to reduce pressure ； 2. The pressure relief valve allows for manual adjustment of pressure; if the pressure before the valve fluctuates greatly, adjustments need to be made frequently. A self-acting control valve operates automatically based on a set, objective value, and the pressure after adjustment can be kept constant ； 3. The pressure relief valve requires manual adjustment of the pressure difference; if the pressure before the valve changes, the pressure after the valve also changes, and it cannot automatically adjust to a fixed pressure. Self-acting control valves can automatically maintain stable back pressure or pressure upstream of the valve ； 4. The main purpose of a self-acting control valve is to maintain pressure stability, whereas the primary function of a pressure reducing valve is to reduce pressure to a certain level or below ； 5. Pressure relief valves have a higher adjustment precision, typically 0.5, whereas the adjustment precision of self-acting control valves is generally 8%-10% ；

A self-acting control valve can set the back-pressure to any value not exceeding the front-pressure, and it maintains this pressure at a constant level by adjusting the length of the screw on the valve body. When setting the pressure, the back-pressure must be removed; otherwise, the set pressure will not be accurate

In a control valve, the air supply pressure is the pressure within the pipeline downstream of the valve. When there is a pressure imbalance, the diaphragm in the cylinder of the control valve moves toward the side with higher pressure, until the pressures are balanced

Thank you, that makes it clear now

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