Addem 121 Posted February 26, 2022 Share Posted February 26, 2022 We’ve just bought a Farrier 41. Beautiful boat but the systems on board are a head ache. Biggest issue is regularly losing fresh water because of a stupid purge switch from a caravan HW system, (which I may ask about in another thread.) While we have solved the purge switch issue, the tanks are small (45l) and we easily run out. We have a water maker but the tanks are both below the FW pump by about 1m. So once the pump has lost its prime we can’t get the water back in use. So, is there a reliable FW pump which would self prime when we top up the tanks from the water maker.? The alternative I’m considering is installing a manual vacuum pump in the line but I’d prefer a simpler solution. Quote Link to post Share on other sites
Jason128 6 Posted February 26, 2022 Share Posted February 26, 2022 Most of the diaphragm pumps are self priming. It would be very unusual not to have one of these as the freshwater pump. Quote Link to post Share on other sites
waikiore 484 Posted February 27, 2022 Share Posted February 27, 2022 Yes all the flojet/Jabsco and Johnson diaphragm pumps will self prime -not 10 metres but enough for you. Quote Link to post Share on other sites
vesper1 3 Posted February 27, 2022 Share Posted February 27, 2022 Does the F.W. system have an accumulator ( a small presssure tank with an internal diaphragm filled with nitrogen on one side, 8 litres I think) this could be the answer. I have one in my system it allows the pump to start with no head and then with flow build pressure. It has been trouble free 20+ plus years. Quote Link to post Share on other sites
Addem 121 Posted February 27, 2022 Author Share Posted February 27, 2022 On 26/02/2022 at 7:41 PM, Jason128 said: Most of the diaphragm pumps are self priming. It would be very unusual not to have one of these as the freshwater pump. That’s what I’d have thought but definitely doesn’t. Would it because it’s worn out? I’m not super keen on tossing out the old just to experiment. Quote Link to post Share on other sites
Addem 121 Posted February 27, 2022 Author Share Posted February 27, 2022 15 hours ago, vesper1 said: Does the F.W. system have an accumulator ( a small presssure tank with an internal diaphragm filled with nitrogen on one side, 8 litres I think) this could be the answer. I have one in my system it allows the pump to start with no head and then with flow build pressure. It has been trouble free 20+ plus years. Sounds intriguing. Any ideas on where to get something like that? Quote Link to post Share on other sites
Jason128 6 Posted February 27, 2022 Share Posted February 27, 2022 25 minutes ago, Addem said: Sounds intriguing. Any ideas on where to get something like that? https://discount-marine.co.nz/index.php?main_page=product_info&cPath=333_365&products_id=6710 Quote Link to post Share on other sites
waikiore 484 Posted February 28, 2022 Share Posted February 28, 2022 Lustys have them Quote Link to post Share on other sites
Jon 412 Posted February 28, 2022 Share Posted February 28, 2022 Pump should suck it up Unless it can suck air somewhere ? Quote Link to post Share on other sites
Jason128 6 Posted February 28, 2022 Share Posted February 28, 2022 What Jon said. take it out and bench test at home. Prove the pumps fine then you can ficus on the rest. A little air leak will ruin any ability to suck up, or you will find worn valves in the pump. we had a bad o ring at the top of the tank pipe that leaked, Could only pump out the top 1/4 of the tank, then it sucked in too much air. Quote Link to post Share on other sites
Jon 412 Posted February 28, 2022 Share Posted February 28, 2022 As above, a small piece of anything under a diaphragm will stop it lifting. So bench test, see if it will suck water up a two metres of tube out of a bucket, if not strip the pump, it would still work when flooded but not suck a vacuum Quote Link to post Share on other sites
Spiekaerul 0 Posted February 28, 2022 Share Posted February 28, 2022 Most of pumps are available but if you use self prime pumps which draw water from below (typically up to 8M) without the need for a non-return valve. They are kept outside the liquid marine equipment, and can either be exposed to the elements or within a structure such as a pump house, and driven electrically, hydraulically or via an engine. Quote Link to post Share on other sites
wheels 544 Posted February 28, 2022 Share Posted February 28, 2022 On 27/02/2022 at 8:11 PM, vesper1 said: Does the F.W. system have an accumulator ( a small presssure tank with an internal diaphragm filled with nitrogen on one side, 8 litres I think) this could be the answer. I have one in my system it allows the pump to start with no head and then with flow build pressure. It has been trouble free 20+ plus years. An Accumulater only acts as a shock absorber. It's stops the pump from "chattering" on switch off. It also smooths the water flow a little. The pressure on the other side of the diaphragm is just air. You set them up by pressurising the thing with the same air pressure as the water pressure switch on the pump is at. The Water pressure always remains at whatever that cut out point is, when it switches off. You can also get accumulators without the pressure bag, but they need continual bleeding of water to keep air in them. The Air dissolves into the Water under pressure and the airspace deminishes over time. Quote Link to post Share on other sites
wheels 544 Posted February 28, 2022 Share Posted February 28, 2022 One of the biggest problems with the the quad diaphragm pumps is the little diaphragms can pull out of place. They have a little centre spigot thing that pushes into a hole to keep the little diaphragm positioned. The number of times I have found pumps that have spat that spigot out of the hole has been numerous. Once that happens, the diaphragm will not seal and the water pressure runs back through the pump when it stops. However, the results in the pressure dropping, thus pump starting and repeating cycle constantly. If that is not happening, then you have another problem. The water should not be able to run back to tank and pressure should remain all the time without constant cycling. It could well be that with only 45ltr tanks, you have a very simple centrifugal pump in the tank, or on the outside of the tank. If outside, they need to be below water level to work. They have no ability to lift water if there is air in the line. They are activated by a switch to make water flow, not by turning on the tap and letting a pressure switch do that job. The one problem with having a pressure type pump on small tanks is that you will use the water up quickly. Most Boats with pressure pumps will have tanks in the hundreds of ltr capacities. Quote Link to post Share on other sites
Addem 121 Posted March 4, 2022 Author Share Posted March 4, 2022 Ok. Thanks I’ll try all those ideas, especially bench test. the pump is rated to self prime to 1.8m so obviously a pump failure. Quote Link to post Share on other sites
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