Working principle of self-acting control valves
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I would like to ask the experts: How does the self-acting control valve in the image below achieve pressure regulation?
This principle should involve comparing the pressure-reduced air supply signal entering the upper part of the valve cylinder with the constant air supply signal at the lower end of the cylinder, or comparing it with changes in other air supply signals, in order to control the opening degree of the valve. It’s best to find a process flow diagram; understanding the principle behind the process in this way is more intuitive, for reference.
The detection pressure signal acts on the diaphragm head of the control valve; under the influence of this pressure signal, the diaphragm on the diaphragm head moves the valve element, thereby opening or closing the valve. When the detection pressure signal balances the spring force beneath the diaphragm, the diaphragm stops moving, achieving automatic control.
There is a pressure sampling point on the diaphragm of this control valve; there is a control valve at that pressure sampling point, and there is also a control valve located below the diaphragm and at the bottom of the valve. That’s the setup in detail. I hope the experts can explain the functions of these three control valves.
A pressure relief valve ensures the stability of the air supply signal pressure.
So how does one set the pressure for this valve? If it’s supposed to be 5.0 MPa, how does one adjust it?
On-site commissioning shall be carried out in accordance with the process requirements, plant parameters, and the instructions provided by the design unit. The pressure reducers used for instrument air supplies of this type are adjusted at the time of manufacture. If adjustment is needed, a pressure gauge is required. For reference.
The opening is adjusted according to the back pressure behind the valve, and there is a gauge tube on the valve leading to behind it.
Self-acting control valves come with various pressure ranges available; select the valve that corresponds to the operating pressure, and it will be able to adjust automatically within that range.