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A (probably stupid) question about priming water pumps


Guest Brucec

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This is something I feel I ought to know, but don't want to get it wrong ...

On a boat I'm working on, the domestic water pump has stopped sucking, following the tank unexpectedly running dry. The tank is now full and the pump is running, but not drawing water - all the taps are dry. It looks like quite an old pump (pics below) and I guess not self-priming. I know very little about this, and everywhere I've looked on the net tells me (somewhat obviously) that I need to prime the pump, but without clearly explaining how.

I'd be really grateful if someone could kindly explain the priming process in simple steps.

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Hi,

Is the pump lower than the tank?

The filter beside the pump is there water in it?

You might have an air lock in the system, if so try just cracking the brass nut beside the pump and let the air out.

Ian :Sailing

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Hi,

Thinking about this I made the assumption the brass nut fitting is on the inlet side of the pump, it is the inlet side you need to get the water into. Does the water pipe come out of the bottom of the water tank or the top?

Ian :Sailing

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Guest DAYTONA-BILL

I would have thought the feed pipe from the tank would come from the bottom, with the pipe inside the tank having an extra length so as to allow "sludge(?)" to lay below the outlet, like in a cars fuel tank. If the pump is lower than the tank, i`d have thought it would be fed by gravity to assist self priming, though i could be wrong. It`s also worth considering if this is an OLD pump, and it`s been allowed to run dry, the internal impellor could have been destroyed, or, as in the case of one of my previous outboards, the rubberised impellor broke free from the centre keyed brass collar. The blades were intact, but the centre was spinning without the blades. Regards ................... Neil.

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Guest DAYTONA-BILL

I know this might sound like i`m taking the arthur, but is there a stop tap on the tank outlet/pump inlet pipe, so you don`t lose all the water when you disconnect it?. If so, check to make sure it`s in the "on" position. This has happened to people before :oops::oops::oops: . Regards ............... Neil.

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Neil,

I agree the pump looks lower than the tank, and therefore expect gravity will prime to the pump. This is why I suggested bleeding the air if there is an airlock bend in the pipework where the pump is. The pump is a diaphragm type pump so it will not have a rotating vane but a rubber disc moving in and out and a set of valves, these needing the water to be fed in on the inlet side to prime the pump.

I suspect the pipe on the water tank needs to be disconnected and a jug or two of water poured down the pipe to fill the pump.

Ian :Sailing

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It should self prime,

if it is refusing to, undo the filter, (it comes apart in the middle) and wait for the water, put it together and turn it on.

I assume the taps are all open?

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Thanks everyone! I'll check tomorrow, but yes, I'm sure the pump is lower than the bottom of the tank. I'll apply your collective wisdom and have a fiddle.

Bruce

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Bruce,

Another thought, I wondered if when the tank ran dry, it filled the filter and pump with crud? I may be wrong, but looking at the colour and type of pipe on either side of the pump, the filter looks to be on the exit side of the pump?? In which case the pump could very well be full of gunk cheers

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Quick update - by following the advice on here it was dead easy. I tried Ian's first suggestion initially, so slackened off the nut on the inlet coupling until a little bit of water ran out of the joint, re-tightened, opened the taps and turned the pump on - it worked!

Thanks everyone for your helpful suggestions. The forum once again demonstrates what a great community it is!

Bruce

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