Questions about control valves
Thread Content
I have a question: since the positioner of the control valve outputs a pressure of 0.02–0.1 MPa based on the electrical signal range of 4–20 mA, does that mean the diaphragm of the control valve uses this 0.02–0.1 MPa pressure as power to open or close the valve? Is the high-pressure control valve for hydrocracking also operated to open and close using this amount of air pressure?
The driving force of the valve is spring force; you can take a look at https://wenku.baidu.com/view/1f22d20c0508763230121252.html
After reviewing relevant materials and based on my own understanding, here is my opinion: the so-called pressure signal in the range of 0.02~0.1 MP does not exist in modern intelligent positioner control valves. That was the case with older control valves; today’s intelligent positioner control valves use electrical signals of 4~20 MA instead of pressure signals
However, the principle is roughly the same; the electrical signal is simply a transformation of the pneumatic signal. The pneumatic signal comes from the pneumatic control panel and acts on the bellows, thereby controlling the amplifier. In modern valves, the bellows have been replaced by magnetic torque, with the electrical signal being used to control the amplifier. Specifically, what pressure can be achieved by the air source used for pressure reduction through an amplifier? It seems that the pressure should exceed 0.1 MP when it’s high. Please point out any mistakes if there are any
The high-pressure control valve for hydrocracking should be at least 0.43 MPa
What is the typical range of air pressure output by the amplifier in a conventional low-pressure control valve positioner (the air pressure supplied to the diaphragm head)?
The instrument air pressure can be selected by the user; it is determined based on the process requirements during the selection process.
The operating pressure is indicated on the nameplate of the control valve, and it is definitely higher than 0.1 MPa