Macerator Problem

[Patrick Ewing]

The Jabsco macerator pump on our 1991 37.5 Legend recently failed us and we were wondering if there is a better alternative to this particular pump.The failure was a result of gasket leakage and the impeller arms breaking.I rebuilt this one and had to get a rebuild kit as well as a new separating plate which was badly corroded. Why is the separating plate corroding? Do you know if it is a result of electrolysis as it appears to occur near to the brass screws. I could replace the brass with stainless easily enough.Would it be wiser to simply get a different pump?Thanks,Patrick

 

[Peggie Hall/Head Mistress]

There's a better alternative, but...

You have it backwards: all the other problems are a result of impeller failure--and your own failure to maintain the pump. Impellers--not only in macerators, but in every device aboard that uses one--should be changed annually, and there should be a spare aboard at all times, 'cuz debris, sand, running dry even momentarily can destroy a brand new impeller. But impellers have a finite, and rather short, lifespan anyway. They're made of neoprene, which is easily degraded by salt water, urine...plus, as they sit between weekends and during winter lay-ups, they dry out...become brittle...and subject to cracking and total failure. Since the macerator has to be downstream of the holding tank and below it, with sewage--including corrosive urine--always in contact with the impeller and pump housing, it's not surprising that a failed impeller would allow urine to eat through the gasket and then attack metal parts. I'm amazed it's lasted as long as it has!Diaphragm pumps are a better alternative...they don't have impellers and don't require any maintenance...the best on the market is the SeaLand T-Series overboard discharge pump.

 

[Patrick Ewing]

People don't fail pumps but ...

Pumps do fail people.I am familiar with impellers and their characteristics and it looks to me that the failure in this case started with leakage of the paper gaskets on either side of the separater plate. This caused the pump to run dry since it was pumping air which ruined the impeller. What was left of the impeller was not cracked or brittle. The impeller did not cause the gaskets to fail and they clearly were leaking.This particular boat is set up so that the pump is not in continuous contact with the sewage. It is physically above the holding tank or nearly so and it looks to me like it lifts the sewage out of the top of holding tank via a tube into the top of the tank. It is a good thing for me or else we would be talking about how to get the sewage out of the bilge since the pump gaskets failed.We rarely even use this pump since we use the sewage pumpout on the dock. With so little use it should not require an annual rebuild. I always pump a few gallons of rinse water into the holding tank to rinse out the system whether I use the macerator or the dockside pumpout. That practice should remove most of the sewage from the pump housing.My previous boat had a diaphram pump and was still working after 20 plus years. Is the SeaLand pump an electric pump or manual? Can I use any diaphram pump for this purpose or is there some other factor I should consider?Thanks for your prompt response. I appreciate it even if we do have some philosophical disagreement.Happy sailing,Patrick

 

[Peggie Hall/Head Mistress]

You just identified the cause of your problem, Pat

Your macerator is above the tank, which means the macerator--and the impeller--has to run dry long enough to lift the sewage out of the tank to the pump. Running dry, even for just a second or two, is the worst thing you can do to any impeller...the edges of the vanes start to overheat immediately, which causes wear--uneven wear--which can lead to leakage and the problems you found...sometimes immediately, sometimes just over time.. Btw...a visual inspection of an impeller won't reveal damage until it's fairly severe. It can look just fine, but still be "fried." Just because what was left of it didn't appear dry and brittle doesn't mean the vanes hadn't dried out. It doesn't take much for it to lose enough of its flexibility to fail.That your macerator is used so seldom is all the MORE reason to replace the impeller--and prob'ly the gaskets too--annually. The less an impeller or anything else is used, the more vulnerable it becomes to failure. Liveaboards have far fewer problems will all systems than weekenders do because equipment suffers more from disuse than constant use. Seals, gaskets, valves dry out from disuse...contract and expand from temperature changes, etc. They'll soften up some when put back into service, but degrade a bit each time...and fail sooner than those used constantly.The SeaLand overboard discharge pump is electric. Only draws about 4.5 amps, so no big deal electrically. More importantly, whether manual or electric, diaphragm pumps can run dry and therefore can be mounted above the tank. And while diaphragms aren't 100% failure-proof, they aren't subjected to the friction heat that impellers are, and therefore are a lot longer-lived. You'll be a lot happier with any diaphragm pump that's rated for sewage handling.