MP gauge question

ChemGuy

ChemGuy

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ChemGuy
How long after making a power adjustment should a MP gauge take to read the new value?

example - idle to FT on take off - mine doesn't read ~29" until rotation, or after.

It does read correct - its just slow. Same in flight when making adjustment you have to adjust throttle and then wait 20+sec for it to read the new setting.

Only plane I have noticed this in and didn't know if it was normal or not.

If its not normal is this a gauge issue or plumbing?
 
It should be instantaneous. Your gauge needs an overhaul.
 
Look for a restriction in the line somewhere - kinked, plugged, or perhaps an orifice has been installed to reduce "bouncing" and has become plugged. But, since I'm not an A&P I don't know how the laws of physics would apply differently to an airplane compared to anything else, so I may be wrong.
 
Capt. Geoffrey hit the nail on the head. Clogged plumbing will cause a slow change in the pressure and thus delayed reading. Whether the clog is in the bung, line or gauge is to be determined.
You can use a hand-held vacuum pump to test the gauge, no need to run the engine.
 
What clogs the plumbing in a vacuum instrument?

Seriously, sluggish MP needles are common. The instrument probably just needs some love.
 
ChemGuy said:
How long after making a power adjustment should a MP gauge take to read the new value?

example - idle to FT on take off - mine doesn't read ~29" until rotation, or after.

It does read correct - its just slow. Same in flight when making adjustment you have to adjust throttle and then wait 20+sec for it to read the new setting.

Only plane I have noticed this in and didn't know if it was normal or not.

If its not normal is this a gauge issue or plumbing?
Click to expand...

Wait, it may not read 29" until rotation, but how long to get to 27"? Is this a fixed pitch or CS prop?
 
The MP gauge may have a bleeder on the line...check to be sure it doesn't have fluid in it....
 
Clark1961 said:
The MP gauge may have a bleeder on the line...check to be sure it doesn't have fluid in it....
Click to expand...

The line on my plane has a loop in it. It occasionally gets filled with fuel (I assume) and the gauge becomes "sticky". We disconnect both ends and blow it out at almost every annual and everything's good again.
 
timwinters said:
The line on my plane has a loop in it. It occasionally gets filled with fuel (I assume) and the gauge becomes "sticky". We disconnect both ends and blow it out at almost every annual and everything's good again.
Click to expand...

With the turbo and a bleeder/drain at the gauge I have the choice of evacuating the line in either direction. Of course the manual sez only let it suck towards the engine...
 
Clark1961 said:
With the turbo and a bleeder/drain at the gauge I have the choice of evacuating the line in either direction. Of course the manual sez only let it suck towards the engine...
Click to expand...

It is the cleaner direction to go with it.

Since a MP gauge is a vacuum gauge, probably easiest to just crack the line at the gauge and let the engine idle for a minute to suck it clear.
 
Never be instantaneous? Mine is. My last one was, and the one before that was. If I adjust from 23" to 24" in cruise the instrument needle goes up corresponding to my movement of the throttle. Ditto for reduction of power. When it got sluggish I got it fixed. I have no idea what yours does but you might should get it tuned up.
 
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