Manifold Pressure Gauge

[RickE]

I recently bought a manifold pressure gauge off Aircraft Spruce in the US. I sent the first one back as it didn't appear to work, they then sent me a second one that had the same problem as the first one which was that the needle indicating manifold pressure was stuck on 30" and would not move when installed.
After a lot of research I discovered that this particular brand of instrument requires power to operate, although it relies on a vacuum hose to supply the pressure. I have never seen an MPG before that required power. You learn something every day!!!!

[mad max]

Kricky!

[RickE]

Kricky!

Am I right in thinking that power to run a MPG is unusual????

[Brian]

Old school thinking [ like me] would say why should you need power to run a mechanical gauge ? but today, its all changed . Yes, we do learn new stuff every day, some things we dont really like learning but other things are interesting & very handy.

[RickE]

[Brian]

Yep, that explains it all ..

[Tim]

My guess would be that it is air pressure compensated to allow for normal variations in air pressure, eg atmospheric, altitude and temperature, which all affect the fine tuning of manifold pressure readings. For that it would need a MAP sensor (as in Fuel injected cars) which is electrically powered.
An accurate manifold pressure gauge can help in more accurate throttle settings and adjustment of fuel mixture as well as diagnosing possible impending engine problems.

[wolfy]

Yep just like a modern car the way things are going, why over complicate simple things.

wolfy

[RickE]

My guess would be that it is air pressure compensated to allow for normal variations in air pressure, eg atmospheric, altitude and temperature, which all affect the fine tuning of manifold pressure readings. For that it would need a MAP sensor (as in Fuel injected cars) which is electrically powered.
An accurate manifold pressure gauge can help in more accurate throttle settings and adjustment of fuel mixture as well as diagnosing possible impending engine problems.

The funny thing is that it was the cheapest one that Aircraft Spruce sell......but apparently the most complicated.

[chook]

Those old mechanical vacuum gauges in the hands of a good mechanic could identify a myriad or problems with engines. The subtlety of the meter movements was the secret. you can't get that with a digital meter as they can't react quickly enough so the readings get "smoothed out".

I have 2 electrical meters, one electronic and one analogue and generally the analogue meter is used more often while I am fault finding.

Regards.........Chook.