Folks,

I have a friend with a Chieftain. The vacuum pumps on his right engine has been lasting between 6 - 150 hours. The vacuum pumps on the left side are almost 400 hours old.

They do have boots, but usually, the failure is not related to use of the boots. For example, the pump recently failed on a flight from Florida to Wisconsin. The boots were not used.

It seems that every time one malfunctions, the drive coupling breaks. This is the area just behind pump, not inside the pump itself.

I do not know their usual RPM operation. I do know that the left engine has about 2400 hours and the right engine has about 1150 hours.

He and his partner fly it ROP at an agreed upon power setting (I do not know what it is).

Any thoughts or suggestions?

Tom

Next time one fails, swap the long lasting left one to the right engine and put the new one on the left engine.

This will provide evidence if it is something about the location (left/right) or something about the quality of the pumps you have been getting.

Mike C.

Ask if he's cleaning out the lines well and replacing the filter.

I would look for pin holes in the boots, while the boots where not used the system applies vacuum to them when not in use. If the boots have many holes in them when flying through rain water can be sucked in through the boot and through the pump.

if I recall correctly the Navajo used a pressure system to run the instruments. Make sure he is changing filters as well.

Is the garlock seal bad allowing oil onto the coupling?

Yes the boots must also be considered.

Next time one fails, swap the long lasting left one to the right engine and put the new one on the left engine.

This will provide evidence if it is something about the location (left/right) or something about the quality of the pumps you have been getting.

Mike C.

Not sure what your serial number is, but most Chieftains with boots use 441CC-7 left engine, and 442CW-6 right engine. One might ask if a left pump was installed on the right engine, would the boots work as advertised. I do not know, but suspect they would still work with only one pump operable, maybe slower to inflate. I also suspect there are shuttle valves to isolate an inop pump, or possibly an incorrect pump producing vacuum instead of pressure, allowing the system to appear to operate normally, on one pump.
Not likely, but certainly worth confirming.

I had this happen several times on my 421 and it turned out the dampener on the back of the engines was bad. Put on another one and never lost a pump again.
I don't know the engines on the Navajo but you might look at something like that.
Keep us posted what you find please.

David,

The Navajo engines don't have the dampener you're talking about.

David,

The Navajo engines don't have the dampener you're talking about.

Take a good look at the pressure system for the boots.

I'm not sure about pipers, but piston booted beech's have a two step regulating valves by airborne. Normal ops, runs the system at 7.5 psi. When you activate boots, regulates up to 18 psi.

If the solenoid that overrides the 7.5psi regulator valve is stuck or clogged, the system will operate at 18 psi continuously - no matter if boots are activated or not. This will wear our pressure pumps quickly.

Also clean filters are essential.

Thank you fellows.

I have passed your comments on to the owner.

Tom