I have a minor question about valves!
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Today, on a whim, I thought of a question: In our factory’s valves, the pressure of the gas supply is 700 KP; after passing through the filter-reducing valve, it drops to 550 KP. This gas at such a low pressure is used to operate the control valves, but the medium inside those valves operates at pressures of 4 or 5 MPa. How is it possible to use a lower pressure to control valves that handle higher pressures? Is it by using different pressures? With a small pressure but a large force application area, the force transmitted to the valve core via the valve stem becomes greater? Also, the pressure at the source under test seems to have no relation to the pressure of the gas source; in my case, the control valve of the 550 KPa gas source can regulate media with various pressures. . Then, how can my valve positioners achieve accurate positioning?
Actually, this control valve has a considerable output force; otherwise, it wouldn’t be possible to regulate the valve. The pressure of 55 OKPA ensures that the pressure remains constant when the valve is fully open or fully closed. When the valve reaches its extreme positions, the output force is at its maximum. During the regulation process, the force output changes as the degree of opening increases. This is mainly achieved through a positioner – by understanding how a positioner works, one can comprehend this mechanism. In the case of intelligent positioners, valve position feedback is sent back to the main CPU, which then uses this information to calculate and adjust the output force. You can look at the following two formulas: 1. For membrane actuators: For a normally open valve, the output force F of FC is equal to (P – P0)XA; for a normally closed valve, the output force F of FO is equal to PLXA. Here, P represents the pressure of the air supply, while P0 represents the pressure at which the valve starts to operate (the pressure required for a normally open valve to close tightly, as it needs a force sufficient to overcome the pre-tension force). A – Effective area of the diaphragm head; PL – Spring force. For a piston actuator, the output force F = π/4ND²(P1–P2). D – Diameter of the piston; N – Cylinder efficiency (a constant value of N = 0.8–0.9); P1, P2 – Pressures at the upper and lower ends of the piston
Open the gas valve, right? I have a valve here with a medium pressure of 3.3 MPa, and it is a gas-actuated valve.
In fact, in the chemical industry, the gas pressure referred to by instruments is actually pressure in physics. In physics, pressure is given by the formula F=P*S, where P represents pressure and S represents the area of the diaphragm or the cylinder. The amount of pressure that drives the control valve to act is determined by the positioner
The poster is already in the fifth grade of elementary school – it’s impossible they would ask such a question, right? Are you teasing us?
Combined with the answer given on the 2nd floor, it is also necessary to use an air filter pressure reducing valve to adjust the pressure of the power air supply.
Reply to 5# bingyusun: My brain froze up; I suddenly hesitated, so I asked to confirm. .
WC? Not bad. Generally, the valve controller is equipped with a nameplate indicating the specific parameters; as long as those parameters meet the requirements, the valve can be closed tightly.
Multiply by the area of the film; the pressure you are referring to is actually stress. If the pressure acting on the film is P1 and its area is S1, while the pressure inside the pipe is P2 and the cross-sectional area of the piston is S2, then: P1XS1 > P2XS2
The gas source pressure is 700 KPa, which is a measure of pressure, That is, the force per unit area. Why does the control valve have a large diaphragm? It increases the area over which force is applied, thereby resulting in a greater output force. The valve positioner ensures accurate positioning of the valve by means of a negative feedback mechanism; the position of the control valve drives a feedback rod, and it is through this negative feedback mechanism that the valve is able to be positioned accurately.