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Henderson pump help needed

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The boat was built in Florida in 1978. I suspect that these pumps are original fitment. I have three one for each shower sump and one manual bilge pump.  I don't use one of the showers and the manual bilge pump gets an annual test then rests for a year. The pump in the shower that I use daily has been in use for coming up to 10 years now and the outer rubber seal which is just a dust seal is showing a small crack and there is a very small leak from the pump diaphragm area. The pump mounting screws look to be the same as the Henderson mk 5 but the front part does not match.

The white ring with the 6 holes has the word Henderson on it

Can anyone help with a pump ID

Are spares kits available. [

I can probably swop in the unused shower pump but would love to have a couple of rebuild kits to hand.



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Yup had a look at the Whale site and the spares kits for a MK 5 Henderson.

Some people say that some modern parts possibly the diaphragm might be the same as the older pumps.

I have yet to strip one of the pumps so don't know what I am looking at. 

I guess I need to think about buying new after all they are 40 years old.

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That looks like an absolutely standard Henderson/Whale Mk5. The rebuild kit will have the diaphragm, flapper valve, joker valve, and some screws. When you rebuild it, don't throw out the large plastic nut that holds the diaphragm to the pump mechanism - they don't give you that, had to dumpster dive to retrieve mine. Most parts are common whether surface or thru bulkhead mount. The bulkhead mount version has a different lever socket and also the rubber bellows and trim ring to finish the inside. These are purely cosmetic. The rubber bellows can be bought separately, not sure about the trim ring. The rubber bellows lasts only about 1/2 or 1/4 as long as the rest of the pump components. The only problem I've had rebuilding them is the screws securing the valves. You need to get these pretty tight without stripping them. 

Henderson worked for Whale but had his own ideas that Whale would not let him pursue, so he went off and started his own company. It was so successful Whale bought them out. At least that's the story. The three pumps on my boat are about 10-12 years old, all of them say Henderson on them even though it's been Whale much longer than that.

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  • 5 months later...

MK 5 ...Size 2 ...mine lasted 30 years before the diaphragm cracked. Henderson Pumps LTD now known as "Whale Pumps"  sells a replacement  pump kit, easily available and is just under $ 60  with next day DELIVERY...

    ( realize this post is months ? Years old? but I am re-doing my pump and thought I would jump aboard and comment.)

This pump is a great design, super simple durable easy enough to work on.

My boat has the same pump & was built in 1978 too,  Copenhagen, Denmark.


I wish the rubber gasket was $6. instead of sixty for the kit..I was thinking of cutting my own gasket out of heavy rubber but it's MOLDED rubber so it 'snaps' into place on it's own for pump-action ...

I am sure there is a trick to making the rubber-molded at home but I went the easy route ( this time. )

With the kit you get the big cap "O ring " and other assorted inlet outlet gaskets.. so that's good I guess. 


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  • 8 months later...

IMO, it's cheaper to by an entire new standard MkV pump, disassemble and use all the parts other than the original front body of the old style bulkhead mount (and maybe the pumping arm lever thingy - can't remember) as this is NLA. This front part is pretty much bulletproof, but check first that it is serviceable. The rubber boot is for aesthetics, not for keeping the water out. No need to replace unless you want to.

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