Hand Diaphragm Pump v Electric Macerator Pump

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Lucy52

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Hi, Katy Louise came with a small holding tank, with a diverter valve to direct the wast overboard or to the tank. The tank is fitted with a macerator pump going to a second sea cock.

I think the hoses are original c20 years old and may be the source of an unpleasant odour. It has occurred to me that I could replace the noisy macerator pump with a hand operated Henderson diaphragm pump. I could then connect this via a Y connector to the other through hull, gaining a quiet pump out, eliminate one through hull and the electrical pump and its circuit. It would also tidy up the under sink cupboard making it more useful.

What do you think, is this a good idea?
 
Well, the Lavac loos use a Blakes/Henderson diaphragm pump which acts as a pretty good macerator. So, if you are OK with the effort involved, there is no problem with the theory. Just make sure you pay attention to loo/tank height relative to the waterline and the need for any bleed holes or loops.
 
You'll likely need 20 minutes of hand pumping to empty the tank, depending on size of course. You could gain an almost silent pump out by fitting an electric diaphragm pump. I have one to flush my Jabsco toilet, almost silent, less prone to blockages and does a fair job of squisherising anything that goes down the loo.
 
Thank you,

I was told that the plumbing was installed by a plumber and the electrics by an electrician, though not as I would like. There is no air admittance valve in the system, only the tank vent. The PO said to keep the sea cocks shut at sea, I’ve found out why. That is another issue to be addressed, both the heads and tank are below the water line. o_O

The holding tank is small, maybe 20 litres, and a Henderson Mk 5 is said to clear more than 50 litres a minute, so it could be emptied quite quickly. I have read that electric diaphragm pumps are more reliable, and the tank could still be teed into the one sea cock, eliminating a hole in the hull. I will consider it.
 
I'm going to throw you a curveball - how about installing a composting loo - Nature's Head is one example of such. A separator loo is another option. I had on my Colvic watson 34 (full time liveaboard) a fancy electric fresh water flushing loo that emptied either into a large (100L or so) holding tank or overboard. Pumpout overboard or of the holding tank was via a henderson pump which actually was the best part of the whole system (so to answer your original question, yes IMO it would be a good diea) which was, to me, a nightmare for maintenance and cleaning. I replaced the lot with a home built separator loo based on a kit from the Swedish company Separett. Absolutely zero maintenence and works really well with no smell...
 
Lucy52 said:
Thank you,

I was told that the plumbing was installed by a plumber and the electrics by an electrician, though not as I would like. There is no air admittance valve in the system, only the tank vent. The PO said to keep the sea cocks shut at sea, I’ve found out why. That is another issue to be addressed, both the heads and tank are below the water line. o_O

The holding tank is small, maybe 20 litres, and a Henderson Mk 5 is said to clear more than 50 litres a minute, so it could be emptied quite quickly. I have read that electric diaphragm pumps are more reliable, and the tank could still be teed into the one sea cock, eliminating a hole in the hull. I will consider it.
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I use a whale gulper diaphragm pump on a 100litre tank which it emptied via a 3 way connector , that many plumbing shops will supply. this allows the holding tank to empty from the head sea cock. I also have a 3 way diverter valve , from head to divert to tank or sea cock. so only one sea cock needed for tank and heads , the pump is quiet and very effective.
My tank is below water line heads not.
My heads are electric with built in macerators
 
V1701, Thanks for the curved ball. I checked out the dimensions of a composting head and regrettably it would be a difficult fit. It would also overwhelm the heads compartment and I would need a larger holding tank. I read up on 'treehuggers' that not is all well with separator loos, they are not particularly liked by long term users, even if I had room for one. Lizzy here has ripped out the holding tank to fit a composting loo in there broad beam. A slightly larger boat. I have looked at small cassette loos, there is some advantage in a marina but as I only have one head compartment it won't work for me.

FlyingGoose, That is very similar to what I propose. The head pump will go to a vented loop, a three way valve either overboard or to the tank. From the tank to the diaphragm pump then connected to the single sea cock via a Y fitting. Diaphragm pumps have a long and good reputation with vacuum heads.

An electric pump are more expensive but would be an alternative. Or for £600 plus fitting I could go with a Tecma Nano: The Nano is an original Tecma design | Thetford Marine which would be quite nice, but I guess a pig if it went wrong.

I would have to block off the redundant through hull until I can remove it and repair the hull.
 
The current set up seems to allow you to keep the second seacock closed unless you are actually emptying the holding tank which prevents any possible backflow through the mascerator to the tank. With your proposed setup you will maybe need a vented loop from the diaphragm pump to the Y piece, and thence to remaining seacock, or the diaphragm pump itself becomes your only safeguard ... personally I wouldnt be happy with that when its all below or near the W/L . Another 38mm dia vented loop can be a bit of a pain to fit when short of space.
 
I agree with PTB. I cannot see any point in removing a seacock, just to have less holes in the boat. It's just making a job and making the pipework more complicated for no good reason.
 
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I think you are right, there is a vented loop shown on the tektanks website. And yes a 38mm loop would e a right pain to install. Thank you, I will have to rethink it a bit.
 
Instead of a vented loop you can also consider a ball valve after the pump .
This stops backflow to the pump
I installed my ball valve ahead of the pump to allow the tank to be completely shut off from accidental flow out or in.
 
Other thing you may wish to keep in mind is that the hand pump and diaphragm pump options are, I think, large bore outlets, 38mm, which, as mentioned, are difficult to manipulate. Your existing set up may well be only 1in outlet from macerator and a 1in seacock. Maybe a new (and hopefully quieter) macerator is the answer if the existing set up actually works OK.
 
Thank you, yes an additional stop valve in the discharge pipe might be an option. Though every joint is of course a potential point of failure which I have to bear in mind. When the tank is emptied there should be no head of wast pressing on the pump to damage the membrane, so there is no need for a stop valve before the pump.

The main seacock is of course 38mm whereas the macerator outlet is 1ins as suggested. An electric diaphragm pump is £220 or so but would be easy to fit with the existing outlet and wiring. I do prefer a KISS solution which is why I would consider a manual pump. There is less chance of failure and it would be easier to repair.
 
I don't think think anyone has confirmed your suggestion that you should change the hose - I would certainly recommend it, my boat (not a million miles from yours!) also had 20-year old hoses, I suspected the general boat pong came from them and changing them got rid of all the smells.
 
Cantata said:
I don't think think anyone has confirmed your suggestion that you should change the hose - I would certainly recommend it, my boat (not a million miles from yours!) also had 20-year old hoses, I suspected the general boat pong came from them and changing them got rid of all the smells.
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Thank you, that is my understanding, though not the most pleasant task. Yours boat has a far more elevated position.
 
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