Should I rebuild my old air pump?

FORANE

FORANE

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FORANE
My old air / vacuum pump failed on the RV-9A O-320. I have replaced it but now have my old pump in hand. Overhaul kits are available from ACS for about $100. I would like to rebuild it and keep it around for when I need another.

Has anyone rebuilt their own air pump? It it relatively straightforward? Would you do it again? Do I need any special equipment?
 
I use ASSCo's kits and they have worked well for me. If the housing is excessively worn, just changing the vanes & rotor may not help.
And you have to be willing to accept the risk associated with such a repair, in light of the importance of the device.
 
If the vanes are allowed to wear too far, they eat up the bore of the pump, leaving chatter marks. New vanes and rotor won't last too long.

Best to buy a pump with the inspection port (Rapco or Tempest) and rebuild it when the vanes reach minimum.

Dan
 
Yeah, on a dry pump you have to inspect it very carefully. Typically if you wait until they break, they've gone too fat for a viable rebuild. I knew one operator who would go through them at 400 hrs and would get 3-4 rebuilds in before replacing, but he wouldn't let them go past 400 hrs.
 
Curiosity got the better of me and I opened up my failed pump.
52gxvc.jpg

It looked much better inside than I expected. Upon close inspection there is a slight amount of chatter marks as Dan mentioned but only between about 5 and 6 o'clock on the pic of the stator above. All the vanes are free floating and dry and intact. I really do not know why the shear coupling failed. Any ideas?
It is tempting to replace the shear coupling and move on.
 
By my eyeball and admittedly not having it in my hand with an inspection light, I'd say your vanes are about due for replacement. More better you do that than wait until you have shattered carbon all over your pump.

That shear coupling broke for a reason.

Jim
 
weirdjim said:
By my eyeball and admittedly not having it in my hand with an inspection light, I'd say your vanes are about due for replacement. More better you do that than wait until you have shattered carbon all over your pump.

That shear coupling broke for a reason.

Jim
Click to expand...
Jim

I think I discovered the reason for the failure. I deconstructed the drive end and found some evidence of dampened carbon dust. It was limited to the shaft - the inside of the pump was completely dry and vanes were free. Recently I had cleaned the motor and I suspect some water got past the seal where the shaft enters the pump. Could be wrong as this is entirely new to me...

This experience with a failed pump got me wondering about my old air pump on the Lancair. It has worked flawlessly since I bought the plane some 800-900 hours ago. It is a Sigma-Tek 1U128-006. I looked but cannot locate any overhaul kit or parts for it. Is overhaul not an option on the Sigma-Tek pumps?
 
Those vanes are fine. Something either stopped the pump--maybe the gunk on the shaft like you say--or that plastic drive was just plain old. They do age, even when they're not turning. Or maybe it had a casting flaw.

Dan
 
Dan Thomas said:
Those vanes are fine.
Click to expand...


You are probably right. I took those dark spots at the end of the vanes on the port side of the photo to be burned carbon. I now see (put my glasses on) that they are simply where the vanes have sucked back into the rotor.

Thanks,

Jim
 
Tempest SL-001...

"...Conditions such as heat, oils, solvents may shorten the useful life of the urethane shear coupling. To prevent failure, Aero Accessories, Inc. recommends the coupling be replaced every six (6) years..."
 
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