In what situations can a control valve be changed from air-operated open to air-operated closed (or from air-operated closed to air-operated open)?
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In what situations can a control valve be changed from air-operated open to air-operated closed (or from air-operated closed to air-operated open)? The specific method?
Ask the manufacturer to make changes! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! There are still tests to be done! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !
A double-acting version is possible; all that’s needed is to change the air inlet and outlet methods
Whether a control valve is air-open or air-close is determined by the requirements of process safety conditions, and cannot be changed arbitrarily by instrument technicians. If a change is needed, for pneumatic diaphragm valves, it is necessary to adjust the position of the actuator spring as well as replace the valve stem. For cylinder-type double-acting systems, the method mentioned above works; for single-acting systems, the manufacturer will need to make modifications. . . . .
The choice between air-open and air-close operation for control valves is determined based on the process requirements; it can be changed if necessary, but it’s best to have the manufacturer conduct tests. Additionally, if valve positioners are used, those also need to be modified. . . . . .
It seems that the positioner can adjust the reaction force, but it cannot change whether it operates in air-open or air-close mode
I don’t know about other factories. Emerson’s can be changed freely. I know how to make the changes; there’s no need to contact the manufacturer. Their valves and cylinders are designed to function in two ways. Just replace a few air vents and adjust the valve’s travel, and that’s it.
Smart positioners can be set for air-open and air-close! For example, the Siemens PS2 intelligent locator changes these two values: “7, SDIR” and “38, YDIR”! The non-intelligent locator with gas-shut-off function requires not only changing the air intake location from below to above, but also adjusting the length of the valve stem!
Valve engineers in Wuzhong say that for their valves, it is sufficient to remove the diaphragm head and install it in the reverse direction in order to switch between the FC and FO modes of operation. Also, as mentioned above, single-acting valves are more difficult to modify, while double-acting valves are easy to modify.
The selection between air-open and air-close for control valves is determined based on process requirements and safety considerations in emergency situations. Normally, replacement is not allowed. If there is no spare valve, I wonder whether it is possible to change between air-open and air-close modes by adjusting the parameters of the locator and the current output from the controller Solve
I’ve done single-acting valves that can be switched between open and closed modes, and it’s indeed quite troublesome. You have to disassemble the cylinder, align the gear positions, and then reassemble it; the gear positions must be exact, otherwise the stroke of the valve won’t be sufficient. Disassembling and reassembling the cylinder is also a hassle – you need to use air pressure to help, as it’s difficult to do manually. I had to drive at that time as well; that’s why I did it. It’s still etched in my memory to this day, haha