Vacuum Pump Shelf Life

[Llewtrah381]

Right now my Warrior is in Annual and the vacuum pump has 425 hours on it (in 2 years). Chatting with the shop, they don’t recommend replacing it right now, even though there will likely be about 700 hours on it at next year’s Annual. I agree with that but also don’t want to get stranded on the road if I can avoid it. With the kind of trips I’ve been doing (plus the AI and DG being overhauled last summer and all the vac lines and filters replaced) I suspect it’ll make it to 700 hours as is.

I’ve heard of (and seen) people carry a spare pump with them. Any sense of the “shelf life” of these, new and rebuilt? I don’t want to carry one for nearly a year just to have it die after a few hours if I need it on the road. I’d have it put in at next Annual if not used. In hindsight, the last one went about 700 hours and was working fine when replaced due to hours.

I still use steam gauges and am happy with that.

 

[Jeff Oslick]

What brand pump is it? Failure before 1,000 hrs is pretty rare. We have a Tempest, and use 1,000 hours as our preventative maintenance replacement time for the vac pump.

 

[Checkout_my_Six]

What does the manufacturer say?....or does a comment from the internet work?

 

[Llewtrah381]

Fair point. I have a call into Rapco to get their input; the issue wasn’t noted on their FAQs.

And, to my surprise, theirs are actually warranted for 3 years/1300 hours new and 2 years/1000 hours rebuilt. My (apparently dated) experience was to replace them around 500 hours. Still, a warranty doesn’t do me much good if I’m in the soup at the time it fails and am on the road. Because it’s a moving part, I wasn’t sure if sitting in a box for years shortened its life.

 

[Llewtrah381]

Well, that was quick. And shame on me for not calling Rapco first.

No real shelf life. The only time-related thing was the shear coupler, which they recommend replacing after six years OF USE because of heat and wear.

It was reassuring to see their warranty. I think I’ll feel more comfortable going a few more hundred hours before even thinking of carrying one.

 

[Checkout_my_Six]

If it's packaged properly....with moisture absorbing desiccant....it should store for years. The warranty is only good from the point of sale...so, you likely will blow thru that.

 

[schmookeeg]

Oh this is a timely thread, I was just about to replace my rapco pump preventatively, only because once the motor is hung, it's a nightmare to get out. I'm about 600 hours on the current pump and had the "500 hour" mantra in my head also.

Might just eat the core charge and leave it on the shelf then.

 

[Dan Thomas]

I keep endlessly pointing out that both Rapco and Tempest have vane wear inspection provisions on their pumps. Start inspecting at 500 hours, every 100 after that, until the vanes are at the wear limits. Takes five lousy minutes to do, and if the vanes are fine the risk of pump failure is tiny. Most pumps fail because they're run until the vanes get too short and cock and jam in the rotor, breaking it. So most owners run them to failure, or replace them far too early because they still don't know, after 20 years already, that the manufacturers figured it out long ago so they could maximize pump life with no risk.

Sigh.

 

[Gary Ward]

I keep endlessly pointing out that both Rapco and Tempest have vane wear inspection provisions on their pumps. Start inspecting at 500 hours, every 100 after that, until the vanes are at the wear limits. Takes five lousy minutes to do, and if the vanes are fine the risk of pump failure is tiny. Most pumps fail because they're run until the vanes get too short and cock and jam in the rotor, breaking it. So most owners run them to failure, or replace them far too early because they still don't know, after 20 years already, that the manufacturers figured it out long ago so they could maximize pump life with no risk.

Sigh.

Isn't the plastic coupler is the weak point before the vanes wear out?

I don't think you could check the vane wear on my old one?

But sure could on the new rebuilt one.

 

[Checkout_my_Six]

I keep endlessly pointing out that both Rapco and Tempest have vane wear inspection provisions on their pumps. Start inspecting at 500 hours, every 100 after that, until the vanes are at the wear limits. Takes five lousy minutes to do, and if the vanes are fine the risk of pump failure is tiny. Most pumps fail because they're run until the vanes get too short and cock and jam in the rotor, breaking it. So most owners run them to failure, or replace them far too early because they still don't know, after 20 years already, that the manufacturers figured it out long ago so they could maximize pump life with no risk.

Sigh.

What are you measuring? It takes more than 5 minutes just to remove the pump. Here's an analysis of how vac pumps fail....

 

[Gary Ward]

What are you measuring? It takes more than 5 minutes just to remove the pump. Here's an analysis of how vac pumps fail....View attachment 103901

Remove the blue allen plug is how you check for wear in my second picture.

I found this wore twice now and the pump was still good.

 

[Doug Reid]

I can tell you from experience, it only takes a few drops of oil getting in to a dry vacuum pump to swell the vanes and cause a failure. Most installations are on the top of the accessory case for that reason. I have been to Tempest in the past and had my old pump rebuilt as I watched. They usually run them after repair in a test cabinet for a few hours. If it were me, I might consider installing a new pump before it reaches it's service life if I depended on it for IFR...VFR, maybe let it go a bit longer. Murphy's Law ..

 

[Llewtrah381]

The warranty is only good from the point of sale.

A reasonable assumption but actually it’s from the day of installation, per their website. Great news, IMHO, and makes carrying a spare even more practical

And as for checking, the tech at Rapco said it’s easy and an owner-doable thing. You use the white plastic micrometer-type gadget that comes with the pump and that they (used to) give away at OSH. In fact, to my surprise, the A&P is supposed to give the owner the included “installation and tips” book (linked). Huh…need to ask my A&P if he has one of the micrometers around from other installs.

https://www.rapcoinc.com/pdf/Informational Tips/Vac installation for web.pdf

All that said, it’s hard to imagine a measurement of the vanes would have early-warned of the failure you showed above. Maybe that was a very old pump with few hours?

 

[Chip Sylverne]

If something's going to fail, it'll probably be the drive coupling. Bendix recommends changing it every 6 years. Like $25 from Spruce, and a half hour's wrenching.

 

[Gary Ward]

I can tell you from experience, it only takes a few drops of oil getting in to a dry vacuum pump to swell the vanes and cause a failure. Most installations are on the top of the accessory case for that reason. I have been to Tempest in the past and had my old pump rebuilt as I watched. They usually run them after repair in a test cabinet for a few hours. If it were me, I might consider installing a new pump before it reaches it's service life if I depended on it for IFR...VFR, maybe let it go a bit longer. Murphy's Law ..

Yup new oil seal is recommended.

 

[Snowmass]

I am blessed with a wet pump which might go 5000 hours or more. But a dry pump? Very unreliable and I am surprised that the FAA ever permitted them. If I were flying serious IFR the replace at 400 hours. If just to make the gyros turn maybe 700 hours. BTW it is possible to replace your pump with a wet pump the last time I checked for under $1000.

 

[Dan Thomas]

I am blessed with a wet pump which might go 5000 hours or more. But a dry pump? Very unreliable and I am surprised that the FAA ever permitted them. If I were flying serious IFR the replace at 400 hours. If just to make the gyros turn maybe 700 hours. BTW it is possible to replace your pump with a wet pump the last time I checked for under $1000.

You have ONE pump. I had pumps on seven airplanes at a time, replacing them when the measurements said it was time to replace, and NEVER had one pump failure. Not one. Not in 11 years at a yearly total of about 4000 hours per year, sometimes a lot more. At least 44,000 hours with no failures.

 

[Dan Thomas]

What are you measuring? It takes more than 5 minutes just to remove the pump. Here's an analysis of how vac pumps fail....View attachment 103901

Oil or solvent getting into the pump can do that. So can the mechanic, when he clamps the pump in a vise to tighten the fittings. Or when he uses a sealant on the fittings, which the instructions expressly forbid. Or when the pump replaces a failed pump; the vacuum in the lines and instrument cases sucks carbon chunks into them, which then gets sucked into the new pump. It's all in the installation instructions.

It can also happen if the wrong pump is installed, one that is supposed to turn the other way. Too much pressure on the vanes against the wall results, eventually failing the vanes.

Tempest has a neat little seal that helps prevent solvents getting into the pump's drive, which is how oil and solvents get in there and gum up the pump, failing it. A lot of old pumps have a wide-open drive that needs to be wrapped with a rag before cleaning the engine.

Parker (Airborne) pump, typical of most old designs. Note the openings into the drive coupling area:





Tempset pump. No openings into the drive.


In short, blaming the pump for failures induced by poor maintenance is unfair, though I'm not saying that your pump failure is due to that. Pump manufacturers don't include installation instructions with every pump for nothing.

Back in the 1980s I was in the air brake compressor and control valve rebuilding industry. It was absolutely amazing, the numbers and conditions of parts that came back for warranty claims. Pipe ports split by overtightening. Sealant (especially silicone) fouling the internals, sometimes causing compressors to blow up due to lack of oil when silicone got into the oil feed port. Dust, dirt, rocks and sawdust in them from drivers who disconnected the trailer's air couplings and dropped them in the dirt, or by mechanics changing them in filthy conditions under the truck. Compressors worn out in a few hours due to reusing the old, rotted-out air cleaner. And many came back just because they blamed the thing for a fault that lay elsewhere, but they didn't have the troubleshooting skills to replace the faulty item first time around. They'd finally call me after they'd replaced some part several times but the problem persisted. Really. How they ever got an HD mechanic's ticket is beyond me.

 

[Dan Thomas]

Isn't the plastic coupler is the weak point before the vanes wear out?
I don't think you could check the vane wear on my old one?
But sure could on the new rebuilt one.

The plastic coupling is there to protect the engine's gear train if the pump jams. The old wet pumps had a steel driveshaft that had a necked-down section between the splines and the pump itself. It would twist off to protect the gearing.

 

[Dan Thomas]

Tempest wear check. Remove the pipe plug in the back of the pump and look inside. Might need a mirror:



Rapco vane wear check, cutaway view. Remove a small hex socket capscrew on the side of the pump and stick the plastic gauge into it:

Both methods require the prop to be turned a bit to get a vane lined up for measurement.

 

[kshaw]

I have used the EDO brand with 3000 hour life (metal vanes) and have never had a vacuum failure. I believe the Sigma Tek bought out EDO but still sell that model. Get those for the higher reliability.

 

[Gary Ward]

The plastic coupling is there to protect the engine's gear train if the pump jams. The old wet pumps had a steel driveshaft that had a necked-down section between the splines and the pump itself. It would twist off to protect the gearing.

View attachment 103910

Thanks, knew why it is plastic.
Have you ever replaced them as preventive maintenance without replacing the pump? Like say 1/2 way through the pumps life?

 

[Snowmass]

You have ONE pump. I had pumps on seven airplanes at a time, replacing them when the measurements said it was time to replace, and NEVER had one pump failure. Not one. Not in 11 years at a yearly total of about 4000 hours per year, sometimes a lot more. At least 44,000 hours with no failures.

Would they go safely 5000 hours? Why not get a wet pump and never need to measure nor replace? And wet pumps are cheaper per hour.

 

[SCCutler]

Oh this is a timely thread, I was just about to replace my rapco pump preventatively, only because once the motor is hung, it's a nightmare to get out. I'm about 600 hours on the current pump and had the "500 hour" mantra in my head also.

Might just eat the core charge and leave it on the shelf then.

Replace it, full stop.

then buy a rebuild kit from Spruce, fix up the old one and keep as a spare.

 

[Dan Thomas]

Would they go safely 5000 hours? Why not get a wet pump and never need to measure nor replace? And wet pumps are cheaper per hour.

And clean the belly constantly. Lose oil via the separator. Oil on the belly seeps through the rivet seams and creates sticky sludge inside the belly. I've had to spend hours sometimes scraping it out and cleaning it up with solvent so I can work on control cables, hydraulic lines and wiring.

No thanks.

 

[Dan Thomas]

Thanks, knew why it is plastic.
Have you ever replaced them as preventive maintenance without replacing the pump? Like say 1/2 way through the pumps life?

Only if it was a pump of unknown life, on an airplane I didn't control, and it didn't have the inspection provision.

I did replace a fairly low-time pump on an engine that had suffered a prop strike. That's what the pump makers recommend. The shock of a propstrike can damage any gear-driven accessory, including the mags and vac pump and gear-driven alternators.

 

[weilke]

We carry one. Worked out well when it crapped out on one of my partners during a trip. He had a local mechanic swap it out and was back on his way. I don't see anything on those pumps that could go bad while it sits in a box in the luggage compartment.

 

[Snowmass]

And clean the belly constantly. Lose oil via the separator. Oil on the belly seeps through the rivet seams and creates sticky sludge inside the belly. I've had to spend hours sometimes scraping it out and cleaning it up with solvent so I can work on control cables, hydraulic lines and wiring.

No thanks.

A dirty belly never killed anyone but a failed vacuum system pump has. I am not so dainty that I can't clean the belly once in a while. And BTW use non-pumice GoJo instead of a solvent and belly cleaning is easy.