I noticed that the fuselage vent gauge was stuck and removed the transmitter which supplies the gauge with its reading, I also removed the gauge to assess and 'match' the two units after bench testing. I found the internal moving coil to be stuck in the transmitter and as there are no spares available I had no choice but to free it off with lubrication. I then ran the gauge up and down full scale in order to to test the system out.
Normal operating pressure is 2.5psi - 4.5 psi. The system is 'red lined' at 5 psi for safety purposes and 8 psi is the absolute maximum pressure. The most we achieve at ground level is around 2.5psi.
Pictured, the gauge, transmitter and a spare cockpit vent panel
It was all re-fitted back in today and showing the correct reading with electrical power on and fuel pressure without engines running.