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BarryL
BarryL

Posted: Tue Dec 23, 2008 1:05pm

Post Subject: Water Supply System

I am going to buy a 42'long 6' 10" beam lined sailaway canal boat for my wife & myself, and I shall be installing the water supply from the pre-installed 135 litre stainless steel water tank. I need some advice on the water pump & need for an accumulator tank. I propose to use HEP20 15mm pipework & fittings with an inlet stainer before the pump, (Jabsco Parmax 2.9 rated @ 11 ltrs/min(2.4galls), pressure switch on @ 1bar(15psi) off 1.7bar(25psi), the manufacturer states that this pump does not need an accumulator tank, however on the same web site they state that an accumulator tank is an important part of any pressure controlled water system, and are often used in conjunction with hot water storage. I will have a twin coiled calorifier in the circuit, and the system will supply a galley sink, wash basin, domestic type thermostatic shower, and a Thetford C200cs cassette toilet flush. To clear the shower waste I propose to use a Whale gulper 220 14 ltrs/min pump. Can you advise if I need to upgrade the pump and or fit an accumulator? Thank you in advance, BarryL.

Tony-B
Tony-B

Posted: Tue Dec 23, 2008 5:25pm

Post Subject: Water Supply System

Dear Barry, unfortunately you do not provide the model number of the pump so I can not look it up to see what type it is. Domestic water pumps (from any manufacturer) come in three types - ordinary pumps - pumps with a bypass valve - pumps that alter their speed in response to water demand. The important factor in all this is that some manufacturers state that the bypass pumps MUST NOT be used with accumulators, but several months ago Jabsco told me their bypass pump could be. So you must double check the installation instructions and then check with Jabsco technical to see if it is permissible to use an accumulator with that particular pump. The accumulator will provide a store of water under pressure so the pump stays off for long periods when no water is being drawn. Without one you may well find the pump runs for a few moments every two or three hours. It will also lengthen the time between the pump turning off and on again when you are drawing less water than pump output (except with the last type of pump - that one just slows down and stays running). It will not stop it, but will lengthen the period so it might seem you have stopped the cycling when (say) filling a kettle but it would still cycle when (say) taking a shower. Do not worry overmuch about the pump cycling. Please also be aware that the accumulator could also be used as an expansion vessel, the differences are the pressure it is set to and where abouts in the system it is situated. As long as the pump manufacturer does not specifically ban the use of an accumulator with that particular pump the choice is yours. I use one. I can not advise on the pump capacity because I have no idea how many outlets you intend to have one at any one time and the flow rate of the various taps and outlets, but my gut feeling is that it will be OK. If you try to draw more water than the pump can supply the pump will run all the time and the pressure will drop until the flow from the outlets balances the supply from the pump. I suspect you would do well to make the main run of the pipework from pump to calorifier (assuming the pump will be at the front of the boat) in 22mm to minimise pressure drop, but I doubt budget boat builders would bother so the choice is yours. Much more information is on my website in the mechanical course notes under water systems. www.tb-training.co.uk (all on one line. Come back if you need more advice. Tony Brooks

BarryL
BarryL

Posted: Wed Dec 24, 2008 4:57pm

Post Subject: Water Supply System

Thank you for your prompt reply Tony, The good advice you have given here and on your web site has convinced me that I need to fit an accumulator tank. Just the problem of the pump running every few hours was enough as we have experienced it on hire boats and our pump will be located near the bed! I have requested (but not yet received) confirmation from Jabsco technical that it is permissible to use the pump (Parmax 2.9 Model no. 31395-0292) with an accumulator. As you guessed the water tank and pump will be at the front, and the calorifier at the back, so your idea of using 22mm pipe is good! As I only expect 1 or maybe 2 outlets to be open at any one time, I will assume the 11 litres/minute output pump to be sufficient. My only query is what sized accumulator? I have seen 1 to 8 litre versions advertised, but 2 litres seems a good compromise on size/cost, any suggestions? Hope you have an enjoyable Christmas. Barry.

Tony-B
Tony-B

Posted: Wed Dec 24, 2008 7:10pm

Post Subject: Water Supply System

I am not going to comment on the suitability of the pump because both Jabsco & Flojet are part of ITT and I know Flojet say their bypass pumps must not use an accumulator, but I think some Jabsco bypass pumps can. If its not a bypass pump it will be fine. As far as the accumulator is concerned really its the larger the better but usually there has to be a compromise based upon space/size or price. Please make sure the accumulator has a diaphragm inside - some do not. Accumulators with a diaphragm can be mounted in any position and can have the internal pressure adjusted, those without must be mounted upright and really need removing annually and "shaken down" to ensure they are free of water. If the accumulator has a "tyre valve" on it, it will have a diaphragm inside. I estimate my accumulator is about 5 litres. You could even use an upside down lemonade bottle but i would not have a diaphragm! The smaller the accumulator the more often the pump will run and the more likely it is to cycle when (say) filling a kettle, otherwise any is better than none. Tony Brooks

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