Henderson MK5 Pump

[eyesec]

Anyone had any experience of stripping down/refitting new bits in a Henderson pump? I replaced the diaphragm etc in mine last year, however, this morning the pump wouldn't work so on opening the front I saw the diaphragm was totally split along the bottom. Two questions, is there a right and wrong way of fitting the the aluminium backing plate, and how much should I tighten the lock nut, hand tight or as far as it will go?
Ordered new repair kit from ASAP this morning. Price seemed reasonable, £30 all in.

 

[greenalien]

aluminium backing plate

The diaphragm backing plate in these pumps is plastic, with rounded edges, and there should be 2, one each side of the diaphragm. See exploded diagram :
http://www.whale.ltd.uk/popup.php?n=exploded&image=Universal_exploded_diagram.png&w=627&h=429&bgcolor=ffffff

If you've got a split diaphragm, could be that someone previously repaired the pump with a piece of aluminium, and this had a sharp edge. There's a spares kit with the correct bits -

http://www.marinechandlery.com/products/9485/288/bilge-pumps/diaphragm-platepivot-arm-kit-as0561.aspx​

Problem is, of course, that by the time you've bought this kit, plus the standard diaphragm service kit, you're getting on for the price of a new pump...

 

[eyesec]

greenalien, thanks for that, will have to have a better look when I strip it down. Any ideas on the tightness of the nut? By the way, ASAP a lot cheaper.

 

[greenalien]

Given that it's a plastic nut, be very careful not to overtighten it - far better to put some RTV silicone sealant on the threads, then do it up hand-tight. The silicone should stop it from coming undone but it will still be removable in the future.

 

[Pete735]

Aluminium support plates

Contrary to greenalien's comments, the early Henderson Mk5 did have aluminium support plates, mines currently stripped down because the plastic nut fractured earlier this week. Mind you the pump assembly is probably 25 years old so it's done ok.

On reassembly, the curved edges of the ally should face away from the rubber diaphragm.
As to how far to tighten the nut, I did mine up firmly , but not overtightened, last time I replaced diaphragm. That was 4 years ago. Given nut has shattered, I'm wondering if I overdid it, but given its age I suspect it was just time taking its toll. Am going to mould an epoxy one this weekend and try that.

I cannot shed any light on why yours failed as it did I'm afraid.

 

[sailorman]

the 2 diaphram plates should be fitted with the rounded face to the diaphram

 

[30boat]

Yes the old plates were aluminium and the rounded part must face the diaphragm.Put some PTFE tape around the threads to avoid leaks.I had a persistent leak on mine which was only cured this way.

 

[sailorman]

Yes the old plates were aluminium and the rounded part must face the diaphragm.Put some PTFE tape around the threads to avoid leaks.I had a persistent leak on mine which was only cured this way.

also tighten the outer screws first then carefully tighten the plastic nut without twisting the diaphram with the nut

 

[greenalien]

early Henderson Mk5 did have aluminium support plates, mines currently stripped down because the plastic nut fractured earlier this week. Mind you the pump assembly is probably 25 years old

My Mk5 is 25 years old, and it has plastic plates, so those with aluminium plates must be older. Mine still has the original diaphragm, but it's on it's second plastic nut!

 

[30boat]

My Mk5 is 25 years old, and it has plastic plates, so those with aluminium plates must be older. Mine still has the original diaphragm, but it's on it's second plastic nut!

Mine is 30 years old .

 

[eyesec]

Thanks guys for the tips hints etc. On stripping down my pump, the aluminium plates had the curved edges against the diaphragm, no the wonder it split. Anyway, all reassembled with the plastic nut hand tight then nipped up with the shifter, on the job list to check every couple of months. As to the age of my pump, the Lister engine is 1970's vintage, reckon the pump is as well!

 

[divonic]

Many thanks for this helpful thread 2 years ago! I had a small leak from my Henderson/Whale Mk V, coming out of the small breather hole on the handle side of the pump body. It is the toilet pump in my Nicholson 35. Stripped it down expecting a broken diaphragm and found the plastic nut retaining the diaphragm had come loose, presumably allowing water (not solids!) to get the wrong side of the diaphragm. Tightened it up, re-assembled and all is fine. If I hadn't read this thread though, I would have had one of the aluminium plates the wrong way round, and would probably have had a ripped diaphragm after a short while - so thank you for the advice (because the exploded diagram is not that clear on the plates orientation).

 

[30boat]

Many thanks for this helpful thread 2 years ago! I had a small leak from my Henderson/Whale Mk V, coming out of the small breather hole on the handle side of the pump body. It is the toilet pump in my Nicholson 35. Stripped it down expecting a broken diaphragm and found the plastic nut retaining the diaphragm had come loose, presumably allowing water (not solids!) to get the wrong side of the diaphragm. Tightened it up, re-assembled and all is fine. If I hadn't read this thread though, I would have had one of the aluminium plates the wrong way round, and would probably have had a ripped diaphragm after a short while - so thank you for the advice (because the exploded diagram is not that clear on the plates orientation).

That's what we're here for...

 

[eyesec]

Two years since I started this thread, where does it go? Good news, no problems with the pump, the nut is checked every couple of months,no signs of slackening.

 

[vic008]

Pete, are you there? Wondering how your epoxy nut worked out. Anyone have any other suggestions for the plastic nut? Also how would you jury rig the (alloy) diaphragm plate. (NZ here-p&p too expensive)

 

[rogerthebodger]

Ant one know what the spec of the thread of the central nut is. I know it not metric, could it be 3/4" Whitworth by any chance. I had one break once and replaces the nut and 'toggle' with a fabricated stainless one, new one M20 nut.

 

[Burnham Bob]

the major problem i found was the outlet valve. it has four 'lost' metal bits buried in the rubber for wood screws to go into it when you renew it. dead easy to strip the metal bits if you tighten the screws too much then they just rotate and the valve doesn't seat properly and leaks. i used lots of sikaflex as well as the screws when i installed the second outlet valve!

 

[sailorman]

one tip is to loose fit the plastic nut in the diaphragm centre then tighten all the outside perimeter screws/ machine screws then tighten the centre nut. this way the diaphragm doesnt get twisted / distorted

 

[LittleSister]

Support plate orientation - Place your bets now!

Well that's clear then! Should we start a poll?

On reassembly, the curved edges of the ally should face away from the rubber diaphragm.

the 2 diaphram plates should be fitted with the rounded face to the diaphram

Yes the old plates were aluminium and the rounded part must face the diaphragm.

Thanks guys for the tips hints etc. On stripping down my pump, the aluminium plates had the curved edges against the diaphragm, no the wonder it split.

If I hadn't read this thread though, I would have had one of the aluminium plates the wrong way round, and would probably have had a ripped diaphragm after a short while - so thank you for the advice (because the exploded diagram is not that clear on the plates orientation).

 

[rhumlady]

I thought it was just me...