Mechanical gauges do fail. pressure pulsations in the line wear them out. Replaced many over the years. Try another gauge.
Thanks. Based on your experience I was inspired to switch port and starboard gages and the port engine that was reading 5 lbs is now reading 32 lbs at idle. So, yep....failed gage.
The interesting part is once removed, I see the working gage is obviously newer (body and internal bracket look much cleaner compared to the other gage, and has pristine bright white model no. sticker), so apparently this isn't the first failure of one of those gages.
The worrisome part is now that I know the model number I can access the data sheet on the website, and see that the two electrical wires on each gage are suppose to activate a solenoid or whatever to automatically shut down the engine when the pressure is low enough. This didn't happen...if 5 lbs isn't low enough, what is ??
Obviously the pressure wasn't
really that low,
but the gage thought it was, so it should have shut down the engine. So now I need to figure out why it didn't.
If curious, click on "diagrams" at link below to see what I mean. Mine is Murphy A20P-150.
20P / 25P Series | Murphy by Enovation Controls
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(on edit)
Further contemplation of the diagram sheet seems to indicate that perhaps it is only the PABS models that will actually set off an alarm and shut down the engine automatically at preset low pressure.
Then again it looks like the standard P model could be configured for auto engine shutdown, just not pre alarm. My A20P gages do have two wires on each gage....if not for auto shutdown then what would those wires be for ? What do you guys think ?
(I probably should mention, before anyone suggests looking at wiring diagrams, there aren't any except for select systems like the helm toggle wiring, bilge pump system and halon fire system. Pleas to Viking for more wiring schematics have fallen on deaf ears in the past)