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Manifold Pressure "Hunting"

E

ethand

Well Known Member
I have about 10 hours on my RV-10 and pretty much since the beginning the manifold pressure does not remain steady when in level flight. It seems to "hunt" up or down about 1" or so.

I am pulling pressure from cylinder 6 area to the three position AL block on the firewall where the Garmin three wire sensor is mounted. I resealed all those connections and am now wondering if there is something else at play?

Thoughts on a cause or where to start looking?

E
 
Are you using the correct fitting? The fitting to be used for the MP has an orifice, a very small hole, in it which will help to minimize the pulses.
 
Orifice in the line will help a lot and so will tapping off more than one runner and teeing together. Otherwise, you get a sine wave signal whenever the valve opens- wump, wump, wump etc.
 
I have the same setup with MP being pulled off of cylinder 6 on my RV-10. I used McMaster-Carr part num 3820K26. It is installed between the sensor and the block on the firewall.

I went with the .004" which works fine, though the MP takes some time to settle with power changes. A larger diameter may be more responsive, though may also bring back some of the instability.
 
Thank you for the responses.

I ordered the MC part and will also check the fitting at the cylinder.

E
 
Closing this out

I installed the McMaster-Carr gauge vibration damper last night and went flying. Worked great and eliminated the hunting that was going on.

Thanks again for the replies

E
 
E,

We also have MP Hunting in our RV-6.

I purchased 3820K26 from McMaster-Carr and it arrived yesterday.

When looking at the plug end I cannot see the 0.004" diameter hole.

Hmm, so I went to the garage to look at my smallest drill bit which is a #60 and it is 0.04".

The drill bit is pretty small and amazingly it is 10 times the orifice diameter of 0.004"

So am I correct, in that the orifice hole is in the plug end, but it is so small I cannot see it?
 
fbrewer said:
E,

We also have MP Hunting in our RV-6.

I purchased 3820K26 from McMaster-Carr and it arrived yesterday.

When looking at the plug end I cannot see the 0.004" diameter hole.

Hmm, so I went to the garage to look at my smallest drill bit which is a #60 and it is 0.04".

The drill bit is pretty small and amazingly it is 10 times the orifice diameter of 0.004"

So am I correct, in that the orifice hole is in the plug end, but it is so small I cannot see it?
Click to expand...

You really should be able to see a .004" hole with your regular readers or 10x loupe that you keep in the tool box.

My 2c is that .004 is smaller than I would prefer. Failing other looking devices, CMW has a proper microscope in the shop.

And, guys, we fly experimental airplanes. The very least we can do is make our own restrictor fittings :).
 
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Adjustable Orifice

I am still building, but in anticipation of the pulsing effect, I installed a small brass needle valve on the Van's manifold on the firewall to dampen the pulses. The valve will probably need adjustment after I am flying, but it will be easy to do.
 
scard said:
And, guys, we fly experimental airplanes. The very least we can do is make our own restrictor fittings :).
Click to expand...

Scoot, ha!

Yes indeed. My partner gave me a technique to look through the damper plug.

Point it at a white piece of paper that is allumination and get close to the fitting and look through from the female end.

Magically, I could see the 0.004" hole.

Crazy.
 
I drilled a .040 hole in a rivet, stuck it in the vacuum tubing. Cheap, light, simple and works great.
 
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