Plugged/Unplugged Vent of PSV

Some of the PSV's are coming with plugged (red sign with PSV) from manufacturers to make site hydrostatic test after installation on the process. Some of the PSV's plugging on site to make hydrostatic test.

All the plugs are must be removed after hydrostatic tests, before operation.

Regards,

I thought that the balanced valves would vent to indicate that the bellows had broken and you were now exposing the back of your relieving piston to the back pressure of the flare/vent system. No need to do this on the conventional valve since the relieving piston is already "seeing" the back pressure of the flare/vent system.