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NBKent...
NBKent...

Posted: Mon Jan 15, 2018 11:26am

Post Subject: Repressurising domestic water system after pump servicing

Hi, I have recently noticed our water pump seeming more laborious, taking longer to kick in when you turn the tap on, longer to switch off again afterwards etc. Read some useful threads here and checked some you tube footage on diaphragm pumps. I took the pump off, dis-assembled it, descaled the diaphragm, checked all apertures were unblocked and motor turned freely, checked and cleaned clip-in filter and reassembled. I tested the pump directly on the batteries - it runs fine. Also used a digimeter to check the electrical supply in-situ to the pump, also fine. I also read up about the little screw adjuster for fine tuning the pressure sensitivity and understand what that does. So I reinstalled the pump, opened the water stopcock and switched the power supply for the pump back on. Cant get it to activate with any amount of turning taps on. Also have a spare pump, so I tested this on the batteries (it works fine) and installed this one instead...wont activate either. I'm guessing I've now got insufficient pressure in the water piping to activate the pump at all and quite likely some airlocks too. I've put the original pump back on because its newer and quieter, but still dead. Am I missing something really obvious here? Have checked pipework for leaks and found nothing. Also ran cabin bilge pumps in case they surprised me by chucking out loads of water, but both ran dry. How do I chase out any airlocks and get the water pressure back up to an operational level? The pump is a seaflo 41 series 35psi (4 diaphragms) and the boat is a 1980 Hancock & Lane norseman. Any nuggets of wisdom very gratefully received....Tim

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

Posted: Mon Jan 15, 2018 1:13pm

Post Subject: Repressurising domestic water system after pump servicing

The micro-switch in the end of the water pump closes with LOW pressure, not high so if the pump will not run you will have all but zero pressure in the system so the switch should be closed and thus the pump should run. These diaphragm pumps are self bleeding as long as you leave some taps open so air cannot be a problem. If you had not mentioned the other pump I would have said that I thought you had a pressure switch problem but that is unlikely to be the case on two different pumps. Have you been twiddling the adjusting screw on both pumps? If you have maybe its so far out of adjustment the switches can not close. Have you stripped the spare pump? If so maybe both pumps are incorrectly assembled so the pressure switch is being help open. I suspect that you have a problem with whatever type of connectors you are using to connect the flying leads on the pump to the boat's wiring. If I had to guess I would suggest that one of the wires on the boat system is not making proper contact with the connector system, possibly because you manipulated it when you took the pump off. I would carefully stick a pin through each cable (two pins) on the pump and measure the voltage present with the pump switched on. If the meter reads zero or close to it you have a bad connection between the pump and the battery negative & positive terminal. If it reads 12V and the pump is still not running then the problems further long the cables towards the pump. Likely places to look are the pump switch on the boat, the fuse/circuit breaker, the positive and negative bus bar connections on the distribution board. if you have a bad connection on either cable run you can get 12V with the pump turned off but as soon as you turn it on the voltage drops to zero. I am sure this is an electrical fault, not a pump fault.

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

Posted: Mon Jan 15, 2018 2:09pm

Post Subject: Repressurising domestic water system after pump servicing

Further info - once you get the pump running and the system bled and if you have an accumulator and/or an expansion vessel it might be a good idea to re-pressurise them. Accumulator at around pump cut IN pressure (say half the cut out pressure) and an expansion vessel at about the cut OUT pressure or a little below. If you have neither do not worry about it.

NBKent...
NBKent...

Posted: Mon Jan 15, 2018 2:58pm

Post Subject: Repressurising domestic water system after pump servicing

Thanks for this Tony, I'll do some more investigation. Re your other comment I've only got an expansion tank on the calorifier

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