Why won’t the supply pressure on my pneumatic indicator stay constant?

Try these diagnostic steps.

1.  Make sure the internal tank has adequate pressure and the tank control valve is ON.
2. With no piezometer attached, set the supply pressure regulator to 100 psi.
3. Turn the flow control valve ON, and open the flow rate valve until the digital gauge reaches 100 psi.
4. Turn the flow control valve OFF. The digital gauge should settle around 100 psi. (Supply regulated pressure).
5.  If the the pressure drops below 100 psi, there is indeed a problem with the indicator. If the pressure is maintained at 100 psi, there is probably a problem with the piezometer connection, the piezometer tubing, or the piezometer itself.