Fuel Boost Pumps

billsheila · #1 11-16-08, 07:20 PM

My bird is in for annual at the moment and I am discussing fuel boost pumps with my mechanic. Based on logs it appears my left wing pump may be original (so 43 years old) and the right wing pump was replaced at one point so is 28 years old. Both had shaft seals done about 12 years ago. Neither leak and they work fine. TT in service for the original one is 2500 hours, I can't recall on the one that was replaced.

Apparently there was a service bulletin to replace the vanes in these pumps because they were breaking up, so the replacement was to "nyletron" vanes or some such name. Can't tell if this SB was ever done.

My mechanic (somewhat surprisingly to me) doesn't seem too concerned about doing anything to these pumps, "they work, they are not leaking, so leave them alone" mentality.

Of course he will change them or have them checked if I want to do it. I am looking for opinion and advice on this, experience others have had with pumps, etc?

Thanks

Skymaster337B · #2 11-18-08, 11:28 PM

If it were a dangerous condition it probably would be an AD by now. Most times a SB is for the manufacture to extort money or to cover their own butts for screwing up. The fact is, if your electric boost pump fails the airplane will keep flying...the only reason it is installed is for back-up of your engine driven fuel pump. I know, you use it for engine start; but it can start without it too, using the primers.
The electric pump is designed to leak fuel overboard, out of that little vent if the diaphragm seal leaks. My view is fly it to failure...it's a Skymaster after all...if it's not broken then don't fix it. But! If your pump is leaking fuel (mine did) then by all means replace or repair the pump...or if it fails then replace it right away too. Besides your pump has lasted this long...so it probably isn't the type discussed in the SB...or the SB was an extortion attempt.

#3 11-22-08, 10:50 PM

Hi, Just a bit of FYI. The C337 maintenance manual says to replace these pumps every 10 years. Here in Canada, if you fly them commercially it's a requirement. Privately, it's at the owner's discretion.

sunnysky · #4 01-07-09, 05:37 AM

I have a 337G with Dukes auxillary pumps.
There was a requirement to replace these pumps because of broken vanes which could then go further into the fuel system and cause the mechanical pump to stop working, then engine failure !!

billsheila · #5 01-07-09, 07:41 AM

I was aware of that Service Bulletin (note it apparently never reached the level of an AD). Any new pump was apparently supposed to be labelled to indicate it had the new type of vanes. I couldn't find these on my pumps. In the end, even though the old ones were working fine, I opted to replace them for the peace of mind.