A question regarding air-operated control valves
Thread Content
For a gas-on/off control valve, will it open when the inlet pipeline is cut off (i.e., when the gas supply manual valve is closed)? Some people say that when the intake pipeline is cut off, the diaphragm loses pressure and the valve opens; then where does the air inside the diaphragm go? I have been studying the diaphragm structure for a long time and feel that air shouldn’t be lost; I hope the teacher can provide an explanation.
A pneumatic on-off control valve closes when the air supply is interrupted.
It is recommended to find a manual or books on this topic, or draw a schematic diagram of the principle based on the actual device, and then you will understand it. One can’t engage in arbitrary arguments like a blind man trying to touch an elephant. It is necessary to fully understand the principles of the actual equipment on site. The “air-lock type control valve” you mentioned refers to the state when the instrument air supply is shut off. The pneumatic control valve in a process system is divided into three parts: the first is the valve part (the valve body) that controls the process pipeline; the second part is the actuator located above the valve body (which can be manual or automatic); and the third part is the signal system for automatic control. A complete pneumatic control valve composed of these three parts. The gas-actuated control valve you mentioned refers to a valve that requires an instrument gas valve in order to be opened. The instrument gas valve cannot be opened without it (manual operation excluded). He does not mean that when the valve is in the open position, it will automatically close once there is no instrument air supply. You’re right; without a valve to release the gas pressure in the diaphragm head (cylinder) section, it will remain at its original opening degree. If it is necessary for this part to have the valve closed/opened immediately in the event of an accident, it should be installed at the solenoid valve (which controls the supply/disconnection/ventilation of instrument air), and this purpose shall be achieved through control via power-on/power-off signals.
In the gas-actuated type, the control valve closes when there is gas present, while when there is no gas, the valve opens automatically due to the action inside the diaphragm head
It will open; the sealing performance of the gas circuit isn’t as good as expected. Opening it is just a matter of time
Just find a valve and take a look, and you’ll know.
See whether you choose fault on, fault off, or fault hold. Single-acting, double-acting.
The air supply to the diaphragm head of the control valve enables continuous fine adjustment; without a steady supply of air, it will open under the action of the spring.
A pneumatic shut-off control valve is one that closes the valve in the event of a problem with the air supply; the data sheet indicates FC. When there is a fault with the actuator, or when the output is 4mA or 0mA, causing the valve to lose air pressure, it remains in the closed position. Simply put, there is no instrument air to push against the diaphragm in the membrane head, so it is returned to the closed position by the spring. This valve can be simply determined by checking whether the air supply pipe coming from the positioner is connected above or below the diaphragm head. The exhaust is routed to a silencer located there; in the case of a pneumatic shut-off valve, the exhaust is discharged through pipes to the silencer attached to the solenoid valve.
Since it’s a gas shut-off valve, it will definitely open when the gas supply is cut off. Cylinders with exhaust holes