Normal Valve Operation - continued.

For ordinary valves, do not use home-made leveraging devices. Such devices cause the plug and the valve seat to be damaged (scoring and gouging.) For the first time, in spite of the damage, the valve will close nicely. But after that, in subsequent usage of the valve, the damage will not allow the mating surfaces to come together properly.

Exceptions: In certain cases, especially for large valves, you may need to use leveraging devices for opening or closing. Such large valves should be equipped with automated actuators that  detect the proper end-positions, and respond accordingly. In some cases the management does not want to spend money for the actuators and allows the operators to use leveraging devices. Irrespective of the reasons, manual over-tightening results in valve damage.

To open the valve properly you need to use actions similar to those used for valve closing. Some valves are equipped with “back-seats.” The purpose of the back-seat is to allow the upper side of the plug to seat against it – thereby blocking off any possible leakage along the stem. If you over-tighten the handwheel during the opening operation, you are likely to damage the back-seat. You should open the valve as much as you can, then back it off a quarter turn or so.