How to change the valves FO and FC on-site?
Thread Content
The valves have been purchased. How can the FO and FC values of the valves be changed on-site? Please explain in detail, thank you!
These FO and FC valves exist mainly for safety reasons. I’m not sure whether the valve in question is a control valve or a switch valve; if it’s a control valve, then the gas path needs to be adjusted. The spring in an FC valve is located on top, while that in an FO valve is at the bottom – making the necessary adjustments will resolve the issue. Another factor to consider is whether the valve actuator is intelligent; if so, some of these actuators have indicators indicating \"air to open\" and \"air to close\", and you can simply adjust it manually to the appropriate position. If it is a on/off valve, it is also necessary to consider whether it has a single cylinder or a dual cylinder, as well as whether there is a spring present; the positional relationship between the valve body and the valve seat must be changed, and the limits must be adjusted again. Due to a procurement error by the company, we had to replace the FC and FO values of several switches, valves, and control valves at the workplace. It’s not complicated; if the original poster wants to know more, it would be better to take some photos and send them over, as that will make things clearer
Pneumatic diaphragm control valve, single-acting – how can FO and FC be adjusted on-site? Is it to adjust the position of the spring in the membrane head? Where is the air intake? If only the locator is modified, then in extreme conditions where both the air supply and power supply are cut off, the valve is reset by the spring force; yet its state remains unchanged. Thank you for the advice from above!
The second floor explained it in great detail: the spring inside the diaphragm changes position, with the upper and lower positions of the diaphragm swapping places; meanwhile, the air inlet and outlet at the diaphragm end also swap places.
The view on the second floor is clearer. It is recommended to consult the manufacturer to find out whether the valve you purchased can have its FO/FC settings changed. If that’s possible, ask the manufacturer to make the changes; if not, replace the diaphragm head. If you’re not completely sure, it’s better not to change the settings on your own. If problems arise and the manufacturer refuses to provide support, and you’re not able to fix them yourself, things will get very bad.
This can be resolved by changing the front and back sides of the actuator; it cannot be achieved using a positioner.
FC or FO refers to the actuator used for this purpose; in other words, there is a spring on only one side of the diaphragm box, while the other side is connected to instrument air. To modify the FC or FO characteristics of the valve, simply remove the diaphragm box and install the spring on the other side of it. However, it is worth noting that changing it from air-on to air-off requires reducing the number of springs appropriately, while changing it from air-off to air-on requires increasing the number of springs. As for how much to increase or decrease, it needs to be recalculated based on the process parameters (mainly the shutdown pressure difference), and the locator must be readjusted after installation. If changes are made arbitrarily without calculation, it may result in the valve not closing properly. Therefore, it is best to have the manufacturer carry out the work.