New style vacuum pump

[PaSkyhawk]

Over the past 10 years I’ve had vacuums pump fail three times while I was flying. The last time was on my Skyhawk. After reading horror stories from other people’s new vane pumps failing after a few hundred hours I decided to try something different for a replacement. The Sigma Tek double acting piston pump seemed like a better design, less chance of sudden complete failure. It’s PMA’d and warranted for 2000 hours but not a long track record in the field. They say they have been running them in pipe line patrol planes. I only have 10 hour on it so far with no problems. There is a slight flutter on the vacuum gauge at low RPM, I’ll let you know how it holds up. It was about $600 and my mechanic said the installation was a little harder than just replacing the old pump. Anyone else have one?

Rich

 

[Tom-D]

I'v never had a venturi fail..

 

[Bill]

I'v never had a venturi fail..

in VMC.

 

[PaSkyhawk]

I'v never had a venturi fail..

I tried that on one student's airplane, hard to set the DG before takeoff

Rich

 

[Tim]

Over the past 10 years I’ve had vacuums pump fail three times while I was flying. The last time was on my Skyhawk. After reading horror stories from other people’s new vane pumps failing after a few hundred hours I decided to try something different for a replacement. The Sigma Tek double acting piston pump seemed like a better design, less chance of sudden complete failure. It’s PMA’d and warranted for 2000 hours but not a long track record in the field. They say they have been running them in pipe line patrol planes. I only have 10 hour on it so far with no problems. There is a slight flutter on the vacuum gauge at low RPM, I’ll let you know how it holds up. It was about $600 and my mechanic said the installation was a little harder than just replacing the old pump. Anyone else have one?

Rich

Everything wears out sometime. Nobody remembers what an improvement dry pumps where over wet pumps anymore. Or why everyone went to them anyway. Back when I use to work part 135 I saw pumps go to TBO but most of the time they did about 1/2. Once in a while you had one that just died.

You should see what a malfunctioning wet pump will do to a plane when it catches on fire.

 

[Tom-D]

I tried that on one student's airplane, hard to set the DG before takeoff

Rich

Why? Set the runway heading before throttle up, and hold that heading? It'll work until you blast off in to 0--0 conditions.

 

[Everskyward]

I guess these guys are hoping you forget...

Maybe the new version is better than the old.

Years ago I had a wet vacuum pump fail and lost a lot of oil out of it. I think the only reason we didn't lose more was that it was in a C-206 aerial survey airplane with a camera hole and viewfinder in the floor. The camera operator said to me, "Can't see anything in the viewfinder, it's all brown." Not a good sign.

In a non-modified airplane there would have been no way to tell until much later. Even if I had seen the AI fail I wouldn't have suspected that we were also losing oil.

I can remember the mechanic telling me the dry pumps fail more often than wet pumps, but wet pumps have the potential for other problems, like loss of oil.

 

[ScottM]

On the Airwolf page they talked about dry pumps failing if you turn the prop backwards. When I need to move the prop out of the way to put on the tow bar or put in the cowl plugs I often move the prop backwards. Is this really a bad thing to do?

I am wondering since I had a vacuum failure two weeks ago.

Scott

 

[dogman]

I guess these guys are hoping you forget...

http://www.airwolf.com/Default.aspx?Pg=ProdWetVacPumps.htm

My Cherokee six has the Air wolf wet pump. It had a problem with it throwing more than normal oil out on th belly throught there air oil seperator. The problem is that My mech. asked them about it at OSH and they pulled him to the side and said yes they have had some problem and to send it back and they would fix it. So at this time we stuck a dry pump on the Six and the wet one has returned to Air Wolf. But what to do? Leave the Dry on or go back to the wet pump made by a company that is Full of B.S. , trying to keep there problem quiet.

Dogman

 

[gismo]

On the Airwolf page they talked about dry pumps failing if you turn the prop backwards. When I need to move the prop out of the way to put on the tow bar or put in the cowl plugs I often move the prop backwards. Is this really a bad thing to do?

I am wondering since I had a vacuum failure two weeks ago.

Scott

Some but not all dry vacuum pumps have the vanes angled and are therefore only intended to be used with a particular rotational direction. This type of pump always has a "CW" or "CCW" in the model number. That said, I wouldn't worry about turning the prop backwards by hand if I had a pump with angled vanes. AFaIK the only time this might cause a broke vane is if the pump is so worn that the vanes are about to break anyway, probably on your very next flight. During normal operation, centrifugal force (inertial actually) pushes the vanes into the pump body fairly hard and this force is missing when you turn by hand.

 

[PaSkyhawk]

On the Airwolf page they talked about dry pumps failing if you turn the prop backwards. When I need to move the prop out of the way to put on the tow bar or put in the cowl plugs I often move the prop backwards. Is this really a bad thing to do?

I am wondering since I had a vacuum failure two weeks ago.

Scott

The piston pump is bi-directional, which was a small factor in my decision to buy it. The redundant valves and double acting piston were more of a factor.

Rich