"Peter"  wrote in message
news:rma7p3l6dbjkb1p4ci396ivsdmgh7r566i{at}4ax.com...
>
> WingFlaps  wrote
.
>>
>>Gauge pressure is what drives the oil around the engine.
>
> Well, yes, to the extent that if the atmospheric pressure (and thus
> the crankcase air pressure) was 1000psi the gear pump would not be
> able to push the oil around :)
>

Yes, the oil pump would still work as advertised. It will develop a
differential pressure across itself regardless of 
the ambient pressure. The 1000 or whatever psi will be on both the inlet
side and the outlet side.

A PSIG indicator will work just fine for your application...

> But the oil pump is a gear pump - a constant volume device which is
> going to deliver oil at a constant volume. There is a spring loaded
> bypass valve which regulates the oil pressure after the oil pump and
> the spring on that enforces a constant absolute oil pressure.
>

Again, it is going to be relative pressure, not absolute....
--- SBBSecho 2.12-Win32