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KCBMarine...
KCBMarine...

Posted: Sun Jul 04, 2010 4:59pm

Post Subject: Fresh Water Pumps

We are building a 57ft narrowboat and we have 4 outlets for fresh water supply. Could you advise the type and size of pump required to maintain a constant water pressure, and outlet sizes. Thank you.

Tony-B...
Tony-B...

Posted: Sun Jul 04, 2010 7:36pm

Post Subject: Fresh Water Pumps

Dear Cliff, this question is impossible to answer, especially the bit about constant pressure. Unless you want to spend a lot of money on a complex variable speed pump that senses pressure in the system and varies its speed to suit the demand you will always tend to get pressure variations. Its something boaters who value simplicity live with, although its not a difficult thing to do. You see you need to establish how far you will turn each tap on and do the same every time. You also need to find a way of ensuring the same number of outlets are turned on every time. From that the outlet suppliers should be able to tell you how much water will flow and then you select a pump with just a slightly smaller output. You will get a pressure drop as the outlets run during the first few seconds after opening but then it should level off. I just wish people who pose questions like this would take the trouble to give the background to the question. In this case why is the constant water pressure so important, who gave the initial advice and why could they not answer the question they essentially posed. Frankly I just do not see how anyone can advise on a specific number of outlets until you establish what you need in the way of sinks, basins, showers and toilet flushing. You see this must be a very simple boat to need just 4 outlets, two hot and two cold I presume so no shower. Or perhaps you will have a shower but not toilet hand basin. As I said, impossible to answer because people operate the outlets to different degrees of opening so if this constant pressure is so important perhaps you had better get one of those expensive variable speed pumps. Sorry not to be much help but if you would care to provide more details I should be able to either set your mind at rest over the constant pressure, point out where there may be a logic failure or perhaps give you the answer, but I doubt I can. Tony Brooks

Tony-B...
Tony-B...

Posted: Wed Jul 07, 2010 7:49am

Post Subject: Fresh Water Pumps

I have been thinking about your question in case I could work out a way of giving you an answer, and unfortunately I am still unable to without details about the flow from the outlets. However I realise I may have misunderstood what you intended to ask. If you are talking about a loss of pressure between the pump and any outlet then you need to consider the length and diameter of the pipes. Depending upon exact pipe runs the length between the pump and the last hot outlet could be 100ft or more so to minimise pressure loss it would be better to use 22mm pipes for the main runs with 15mm spurs to the outlets. Tony Brooks

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