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Old 03-18-2020, 02:46 PM   #1
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lavac problem

hi all,

we have a lavac toilet with a henderson manual pump. we've had it for 15 years. aside from 2 diaphragm changes and period duckbill replacemnt it has performed flawlessly.

two week ago we experienced a "lockup". the handle would not move. under sustained pressure it gradually moved but after the up pull the same lockup. after a few repetions it returned to normal. chalk it up to freak accident. then a couple of days ago the same thing happened. today i blew out vent line with a hose but there was no resistance. i also ran a snake through the saltwater intake line again not clogged. the pump is pretty simple and i can't think of any circumstance which would cause the pump to behave like this.

any ideas welcome.
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Old 03-18-2020, 04:16 PM   #2
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We have two of them about to be replaced with something electric. Even when working they seem to be a PITA.
I know this isn't any help, just my feelings about the damn things.
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Old 03-18-2020, 07:22 PM   #3
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If you put something, ah, ... too big... in it, the pump will feel like it is locked. It behaves exactly as you describe, somewhat heavy steady pressure will usually force whatever is stuck in the outlet duckbill through. Sometimes it is possible to have the Too Big thing in the bowl outlet itself, but generally in that case it will just not pump through, not feel like the pump is locked, and can be mechanically dealt with, if required.

Over time (years), there is buildup of calcified deposits in the pump, these can build up on the back of the duckbill and close down its capacity, leading to more frequent blockage. Rebuilding the pump is the solution. You can just disassemble and soak in vinegar for an hour or so, but as long as its apart, might as well replace everything - in a Hendersen everything is just the diaphragm and two valves. Everything comes in the rebuild kit EXCEPT the big plastic nut for the diaphragm - don't throw that out or you'll be diving for it in the dumpster as I once did! The deposits feel like concrete until soaked in vinegar, then they soften up and are easily removed.

The Lavac is the simplest and most reliable head in the world.
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Old 03-18-2020, 07:47 PM   #4
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we only put toilet paper in the toilet and no different than the last 15 years.

just rebuilt the pump last summer. new diaphragm, duckbill, flapper. we used with no problems from nov to now.

i have a brand new pump which will go in tomorrow. i was hoping there was something "outside the box" that i wasn't thinking about.
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Old 03-18-2020, 08:05 PM   #5
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The Henderson MK5 has two pivot points on the rocker arm. If one or both of those pivot points are worn the pump can lock up as you describe.
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Old 03-18-2020, 08:36 PM   #6
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thanks parks.

after i replace with new tomorrow, i will bring pump home to check and hopefully rebuild this summer.
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Old 03-18-2020, 09:14 PM   #7
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The Henderson MK5 has two pivot points on the rocker arm. If one or both of those pivot points are worn the pump can lock up as you describe.
Jeez, good advice from an experienced Marine chandler that knows about this stuff.... Worth checking out, you asked.
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Old 03-18-2020, 11:15 PM   #8
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It’s going to be really embarrassing when I’m wrong. It could be other things too.
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Old 03-19-2020, 06:42 AM   #9
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hi parks,

what else could it be, since i think i've checked the obvious things.

i'll have new pump in by this afternoon but since it doesn't always get in that state it'll take time to conclude it's fixed.
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Old 03-19-2020, 06:55 AM   #10
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The Henderson MK5 has two pivot points on the rocker arm. If one or both of those pivot points are worn the pump can lock up as you describe.
Similar on my Groco Model K head (bronze pump that also has a linkage arm beneath the piston, so not in the effluent flow), I once had it freeze hard intermittently just as OP states on his Henderson. I forget exactly, but something came loose and would jam the linkage. Might have been the set screw backed out. Fix was simple...... once I got to it.
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Old 03-19-2020, 07:31 PM   #11
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new pump is in and is working smoothly. if problem recurs, i will check back in,
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