vacuum problem

Can someone tell me the logical way to check out the vacuum system on a lycoming. I was flying yesterday and all of a sudden no vacuum. My last plane had venturi tubes so I am at a loss. Can I check vacuum at the pump first and then work back into the plane? The suction gage went to zero and the instruments effected died as well.
Thanks

Assuming your gyros also spun down, its probably the vac pump which is by far the least reliable item in the system. All this of course assumes you have a dry type vac pump.

Deene.

I had a new Rapco pump on my Lycoming that went in about 8 hrs. It was replaced under warranty. They say not to use any sealant on the fittings, it could cause premature failure. Very likely your's failed.

Roberta

rv9aviator said:

Can someone tell me the logical way to check out the vacuum system on a lycoming. I was flying yesterday and all of a sudden no vacuum. My last plane had venturi tubes so I am at a loss. Can I check vacuum at the pump first and then work back into the plane? The suction gage went to zero and the instruments effected died as well.
Thanks

Click to expand...

The failure mode on dry vacuum pumps is as you describe, they just quit all of a sudden. Average life is probably 4-500 hours and there are no warning symptoms.

You can remove the pump and spin it by hand--it will be apparent if it's working. Removing it will also let you check if there is an obvious problem like a hose fitting that has become detached.

You can buy rebuild kits. The pumps themselves are stone simple, but may require some machining if scored. You can also buy a rebuilt pump--probably easier.

If you do change the pump, carefully blow out the lines and change the filter, as a failed pump can leave debris in the system which can kill the new pump

If it's an experimental, I would lose the vacuum system and put in one of the solid state replacements (BMA, dynon, etc.)

HTH

James Freeman

I'll pull the pump tomorrow and see what I can see. I am familiar with vane type pumps and how fragile the graphite vanes can be.

Thanks for the heads up.

Vac pumps

Dry vac pumps can be diagnosed easily if equiped with a gauge (mechanical). Assuming the regulator is properly set, vacuum indication should be at normal range at a fast idle (1000 to 1200 rpm). The needle should be steady. A wiggling needle is also an indication that the pump is "suffering" and may be on it's way out. Vacuum filters should be carefully attended to. The use of tefflon tape on fitting should be avoided. Regulators have a "rubber" band filter, and should be replaced at annuals always. They're cheap. Oil leaking from pump drive can seep into the pump and it to is an enemy.
T88

Well, I removed the pump today and the plastic coupling was twisted into. The inside pump was washboard looking but the rotor and vanes were intact. I ordered a rebuilt pump and it should come in tomorrow. Like they say, It's only money!

Thanks for all the help,
Jim