Another Pump Rebuild – Henderson Mk V Bilge/Diaphragm Pump

My service kit arrived today for this Henderson Mk V manual bilge pump, so I took some time this afternoon to rebuild it.  This was the easiest rebuild of the four different type pumps that are on Cay of Sea.

The Henderson pump is actually destined for use as a holding tank evacuation pump.  When we go off shore (eventually), I want to be able to empty the holding tank overboard.  I discuss my refit of the sanitation system on board Cay of Sea here.

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Above are images of the very large and bulky pump body.  The bottom and top halves are fastened with 8 self-tapping screws, and the diaphragm also serves as a gasket between the halves.  The casting and labeling seen above actually identify this pump as a “Blakes Lavac” pump, but it is a Henderson Mk V.  It is supplied by Lavac (and labeled as made by them!) as their preferred pump for their vacuum-operated marine toilets.

There are only a few parts in the service kit:  Two valves, an O-ring gasket, and the big rubber diaphragm are the heart of the kit.  It also comes with new stainless fasteners and snap retainers for pivot shafts.

DSC02444 DSC02445 DSC02446The instructions are useful, including a complete parts inventory reference, plus the various options and requirements for installation.  I was a bit dismayed by one of the parts supplied:  the “joker” valve, or back flow preventer, was distorted and looked to be in worse shape than the joker valve I was replacing.  While the rubber of the new one was slightly more supple, the distortions in shape made me doubt that it would close properly when pulling a vacuum.  I cleaned the old one, lubricated it with dish soap, and reinstalled it. The joker valve is held in place with four stainless screws.  It’s easy to remove and replace.

New joker valve.  It's not supposed to have big gaps in the tri-cornered lips.  You can see daylight through that.

New joker valve. It’s not supposed to have big gaps in the tri-cornered lips. You can see daylight through that.

Here's the old joker valve.  This is the way is should look.  I cleaned and reinstalled this one.

Here’s the old joker valve. This is the way it should look. I cleaned and reinstalled this one.

Here are a couple of photos of the pump halves separated.  You can see the orientation of the valves and diaphragm.

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The diaphragm is moved by a lever which is attached to an actuator arm.  The end of the arm is threaded to received a large diameter nylon nut.  Two large plastic plates mount onto the actuator arm and are secured in place by the nut.  Photos make this easier to understand than text.

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I see now that I forgot to get a photo of the actuator arm without the diaphragm in place.  Sorry, guess you’ll have to refer to the illustration (above) for that.  I did not remove the actuator – there was no need to.

I also replaced the old flapper valve (think of a one-way door) with the new one from the kit.

The new valve comes with a new plastic frame - see the little frame this old valve is attached to?  I cleaned up the seal surface, and installed the new flapper.

The new valve comes with a new plastic frame – see the little frame this old valve is attached to? I cleaned up the seal surface, and installed the new flapper in its frame.

I installed the new diaphragm, reassembled the pump halves, carefully tightened the screws all around as evenly as possible, and continuously checked the gasket contact area for fit and seal. After it was put back together, I checked the pump by inserting the handle into the socket and pumping it while checking for suction with my hand.  It pulled well – unlike before.  I’m not sure which component was the culprit – perhaps an accumulation of little leaks throughout – at any rate, it works now.

I’ll review its installation in the head in another post.

  1. Patrick said:

    How did you determine the problem was with the pump rather than in the hoses leading to the pump (ex, leaks, or a problem priming)? I have the same pump as you, not working at all, but the pump parts look pretty much fine. Hoping to figure out where the problem actually is before buying a rebuild kit.

    • I wasn’t sure, actually, where the problem was. I couldn’t get the pump to move anything, and the only reason I could fathom was that it wasn’t able to create a vacuum, or establish a seal in any direction. That, and I knew all of my other connections were good enough to pull at least some water, but I couldn’t get it to move anything anywhere.

      It had to be either the valves or the diaphragm, or some combination of both. I knew the pump was fairly old, and just decided that it had to be better with new guts, regardless.

      I am willing to bet your pump will be like new when you rebuild it. But it is very difficult to test the pump to determine if there is any air movement, because the spring is so stiff – it’s impossible to hold it still, unless you clamp it down on a bench. However, though it seems like a bit of a shot in the dark, it isn’t really. Hose connections aren’t that complicated, and it’s difficult to get enough air leaks to keep the pump from priming, if you’ve installed the hoses with any semblance of understanding (I’m sure you have). Bottom line: this is a self-priming pump, and a high volume pump to boot. It should have pulled a vacuum within the first couple of strokes, and that would quickly prime the pump. That was my biggest clue that the internals were just too old.

  2. Peter Freeman said:

    I use a Henderson/Whale Mk V pump for the toilet water holding tank discharge on my vessel and it has for some time been the source for increasing odor and a sewerage leak around the area of the 4 screws securing the joker valve. These screws fasten from the outside and pass through the pump body and screw into a metal plate embedded in the base of the joker valve. It would appear that this metal plate is made of some sort of alloy which will corrode if it comes into contact with corrosive substance such as sewerage black water and this can be the case if the rubber surrounding the plate is stripped or damaged during assembly. The problem is that if the 4 screws are tightened to a point which will allow a 100% seal of the joker valve against the pump inner body then there is a possibility that the screws will strip the rubber inside the screw hole and expose the metal insert to the sewerage. If the plate corrodes and distorts and the joker valve seal against the pump body is compromised then this leaves a passage for leakage or vacuum under pressure to the outside of the pump via the screw holes. I understand that this is quite a common occurrence (maybe more often when the pump is used for black water discharge). Maybe the company should advise those replacing the valve to seal around the new joker valve with an appropriate sealer rather than cranking the screws up in the hope of a perfect seal. Maybe also it would be nice if the company offered a replacement joker valve on its own as an item rather that having to pay almost half the cost of a new Mk V pump for the full overhaul kit.

    • Peter, I haven’t had, nor used, the pump for sewage discharge for very long. Sailing on the Chesapeake, one doesn’t have the liberty to discharge in the bay. So my pump hasn’t had any service in the purpose for which I installed it, and consequently I don’t have any experience with the leak you are getting.

      I will say, though, that the pump and discharge line must be rinsed with clear water after each use. I think it’s fairly obvious that there should be no sewage left in the line or the pump, or else a smell is bound to develop, and of course, a corrosion problem as well. Most boat owners are pretty eager to get a good rinse through their holding tank anyway, and it only takes a little extra time to pump a couple of gallons of clear seawater in the tank and rinse the system. I would actually do it several times, until the exhaust water ran clear.

      I’ll be the first to join you in complaining about the cost of rebuild kits for pumps. The price is simply robbery. And I agree that the joker should be offered separately from the rebuild kit, if it’s a part that’s prone to failure. Joker valves for marine heads are commonly available without purchasing the entire kit. Additionally, I was surprised that the new joker supplied with the rebuild kit was so distorted. I was confident it wouldn’t function properly. Hopefully, that was a one-off experience with Henderson parts.

  3. Bob Pemberton said:

    How do I contact suppliers of these rebuild kits ? am located in Zimbabwe and require 12 kits

  4. Steve said:

    Thanks for this. Made the job a lot easier.

    • Glad it helped. When I looked for Internet resources prior to the rebuild, I couldn’t find anything. Fortunately it’s a pretty simple device, and the process is straightforward.

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