Pneumatic lock valve on the valve
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I would appreciate some guidance from experts. As shown in the valve pneumatic circuit diagram in the attached image, how does the lock valve maintain its position? When the air supply at the SIG port is cut off, wouldn’t the air inside the valve cylinder be discharged through the EXH port? Wouldn’t that prevent the valve from maintaining its position? I’m very confused; who knows what’s going on exactly? Thank you all
The fault location of the cylinder valve is determined by the air tank.
The control of this control valve is relatively complex; it is an FC valve (air-actuated). I believe that the lock-up valve here is not used for maintaining a set position, but rather serves as a substitute for two solenoid valves. The control of this control valve involves the two outputs from the valve positioner, which then pass through a pneumatic amplifier and a lockout valve before reaching the cylinder; meanwhile, the operation of the lockout valve is controlled by two solenoid valves connected in series in the pneumatic circuit. I think the designer’s intention was to prevent accidental operation, which is why two solenoid valves were arranged in series; only when both solenoid valves activate simultaneously will it function. Because this is a double-acting valve, it means 4 solenoid valves are required. Therefore, to avoid this problem, 2 lock valves indirectly replaced the other 2 solenoid valves.
Thank you for the advice! So it’s equivalent to a pneumatically controlled directional valve, right? It seems like it’s unnecessary! It’s not very useful?
From the diagram, it is indeed a valve that shuts down in case of a fault; this is indicated on the valve body, and springs are also shown in the upper cylinder. It appears that there is no function for maintaining the valve in its position in case of a fault. Moreover, the size of the actuator should be relatively large; this is why a locking valve is used in combination with pilot elements. I estimate that the air duct leading to the cylinder should be at least 10 mm in diameter. This valve also features a rapid shutdown function, and the exh port of the locking valve connected to the cylinder is likely linked to an emergency air tank. During interlock operations, both air pressure and springs work together to ensure that the valve operates quickly and reliably.
This air circuit doesn’t have a holding function; it shuts down in case of a fault. Moreover, there’s an extra component, namely the SWITCHING VALVE, but its presence or absence makes no difference
I agree that this air circuit isn’t designed for position maintenance in itself; however, without that SWITCHING VALVE, it’s impossible to control the direction-changing function of the air-controlled directional valve. The lockout valve serves to ensure that, in the event of a loss of air pressure, the air circuit is directed to the air reservoir, thereby enabling the valve to shut down in case of a failure
I agree that this air circuit isn’t designed for position maintenance in itself; however, without that SWITCHING VALVE, it’s impossible to control the direction-changing function of the air-controlled directional valve. The lockout valve serves to ensure that, in the event of a loss of air pressure, the air circuit is directed to the air reservoir, thereby enabling the valve to shut down in case of a failure
Upon close inspection, the function of the SWITCHING VALVE is to activate when the air pressure is low; in fact, there is no such thing as an identical one