The self-operated control valve, also known as the self-operated control valve, is based on the pressure and temperature of the medium flowing through the valve itself as the energy source, and uses the reaction signal (pressure, pressure difference, temperature) at the output end of the valve to transmit to the actuator through the signal tube, drive the valve disc and then change the opening of the valve, so as to achieve the intention of adjusting the pressure, flow rate and temperature.
So, the self-operated control valve is divided into self-operated control valve with commander, and the direct action is self-operated control valve, what is the difference between these two types of self-operated control valves, and what are the differences between the occasions in which they are used, including what is the working principle?
1. Direct-acting self-operated control valve:
Also known as tension spring load control valve, diaphragm up and down, either is the comparison of the pressure behind the valve and the tension spring force, or the comparison of the pressure before and after the valve to control the opening of the valve, there are elastic elements in the structure: such as elastic pipes, bellows, bellows type of temperature bag, etc., using the principle of elastic force and reaction signal balance.
2. Self-operated control valve with commander:
It adds a pilot (pilot valve) that amplifies the response signal and then passes through the actuator to drive the main valve disc motion to the intent of changing the valve opening. If it is a pressure regulating valve, the reaction 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 positive force equipment) at the outlet of the valve from both ends of the orifice plate to take out the music difference signal and introduce it into the actuator: if it is a temperature regulating valve, the outlet of the valve has a temperature sensor (or temperature bag) to drive the actuator through the thermal expansion and contraction of the medium in the temperature sensor.
In summary, under normal circumstances, the control accuracy of the direct-acting self-operated valve is not high, and the addition of the commander is mainly to add the control clearance, which can be twice as high as the general direct-operated tuning valve, and the adjustment pressure difference ratio is large (such as 0.8MPa before the valve, 0.001MPa after the valve), which is especially suitable for micro-pressure gas control.
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