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No Vacuum Pressure

N

N536MM

I'm New Here
I'm my RV-6,we have installed a rebuilt Rapco vacuum pump. It is not defective.
The vacuum gauge is good. There is no vacuum pressure when the engine is running. There is not enough vacuum to spin the gyros. I can see some pressure by attaching a vacuum cleaner to the system which leads me to conclude that the gauge is ok. The plumbing seems to be correct with no obvious problems. Does anyone have any idea what else I can check? Thanks.
 
Simple test

Can you use a shot piece of vacuum hose and connect a vacuum gauge close to the pump? Find out what the pump is drawing first. If you have plenty at the pump and none in your system you have a leak.
 
Is this on a new airplane build or installing a rebuilt pump on a system that has worked previously?

If it is a system that worked previously, perhaps you have the wrong part number pump. There are versions for different rotation directions
 
Thanks guys. We have the correct pump. The aircraft is 12 years old. The vacuum has been ok until recently. Maybe the vacuum cleaner can provide enough suction to override a leak where the engine driven pump cannot?
 
Shear Coupling

After reading all the other posts, maybe the Shear Coupling broke or is missing.

There is a Shear Coupling that is designed to break if there is a bind in the system. Maybe the pump is seized and the coupling broke as it is designed to.

The coupling looks like this:

07-03568c.jpg


They cost about $15.
 
Have you checked your vacuum regulator & filter?

If this gadget is stuck open it might be the cause of your problems:

http://www.rapcoinc.com/pneumatics_regulators_product_guide.asp

The filter should be changed on schedule. They get old and crumble and pieces may get sucked into the system.

One style filter example: http://www.skygeek.com/piper-751-815-filter-vacuum-reg.html

Some installations may have a filter that is non integral with the regulator:
http://www.aircraftspruce.eu/rapco-filter-ra2j4-7.htm

http://experimentalairplane.com/vacsys.gif
 
Hey guys,
Great news! One of my neighbors who is a RV-6 owner found two problems. Now I have normal vacuum pressure. The two problems were 1. The vacuum pump exhaust line was completely stopped up by dirt dobbers and 2. There was a fitting that had split. So the exhaust line was cleared and fitting replaced. Now I have great vacuum pressure thanks to Craig French. What a great neighbor!
 
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