Water Pump Issues - What haven't I thought of?

[Trident]

Water pump works and pumps - as does the new one I just changed it to - but it builds pressure so that there is a good flow for a few seconds when the tap opens but then runs to a trickle . Close the tap pressure builds again so a good flow for a few seconds and then a dribble ..

I've changed the pump, checked the tank vent is clear, opened the tank inspection hatch for more venting, checked pipes for blockage, kinks etc, no leaks , pump is 40psi Jabsco, brand new , only has to lift maybe 50cm above the tank and 1.5m total length from tank. I've opened all taps in case of airlocks and all flow water - just very very slowly .

System is tank, strainer, pump, output to three taps for cold and three taps for hot via a 10L calorifier - the rate of flow is the same for hot and cold

I just can't think of anything else to check - any ideas please?

 

[PCUK]

Have you checked the new pump to ensure it is actually pumping correctly?

 

[Trident]

Yes It pumps first when disconnected from the system which means the problem is upstream but there are no blocks leaks or kinks etc …

 

[vyv_cox]

Suction strainer blocked with debris?

I have to say it sounds more like a kink or blockage downstream of the pump. Try disconnecting the pipework at the branch before the calorifier and pump into a bucket

 

[RunAgroundHard]

I experience the same if I run out of water or clean the water filter and then refill the system. The pump is not priming. In my case I have to suck through water on the inlet hose, then fit it and start the pump. It usually takes a few attempts. Exact same symptoms when an air lock is present, initial burst of pressurised water, then a dribble.

 

[geem]

Water pump works and pumps - as does the new one I just changed it to - but it builds pressure so that there is a good flow for a few seconds when the tap opens but then runs to a trickle . Close the tap pressure builds again so a good flow for a few seconds and then a dribble ..

I've changed the pump, checked the tank vent is clear, opened the tank inspection hatch for more venting, checked pipes for blockage, kinks etc, no leaks , pump is 40psi Jabsco, brand new , only has to lift maybe 50cm above the tank and 1.5m total length from tank. I've opened all taps in case of airlocks and all flow water - just very very slowly .

System is tank, strainer, pump, output to three taps for cold and three taps for hot via a 10L calorifier - the rate of flow is the same for hot and cold

I just can't think of anything else to check - any ideas please?

You have a partial blockage. You can build pressure past the blockage when there is no flow. As soon as you get flow the partial blockage acts a restrictor due to the velocity of the water.

 

[PCUK]

That definitely sounds feasible.

 

[Daydream believer]

Have you used PTFE tape on any of the joints & caused a curtain of the tape across the pipe?

 

[SteveG]

Water pump works and pumps - as does the new one I just changed it to - but it builds pressure so that there is a good flow for a few seconds when the tap opens but then runs to a trickle . Close the tap pressure builds again so a good flow for a few seconds and then a dribble ..

I've changed the pump, checked the tank vent is clear, opened the tank inspection hatch for more venting, checked pipes for blockage, kinks etc, no leaks , pump is 40psi Jabsco, brand new , only has to lift maybe 50cm above the tank and 1.5m total length from tank. I've opened all taps in case of airlocks and all flow water - just very very slowly .

System is tank, strainer, pump, output to three taps for cold and three taps for hot via a 10L calorifier - the rate of flow is the same for hot and cold

I just can't think of anything else to check - any ideas please?

Do you have an in-line water filter e.g. Whale Aquasource in the feed? They can present a significant resistance to water flow. I tried the cheaper Pozzani equivalent that claims to be a direct replacement. Not so. The return spring on my galley foot pump is not strong enough to overcome to flow resistance of this type. Works fine with the Whale version though, so I have to pay three times the price for the genuine article.

 

[Trident]

You have a partial blockage. You can build pressure past the blockage when there is no flow. As soon as you get flow the partial blockage acts a restrictor due to the velocity of the water.

It could be that - certainly sounds like the physics of what is being seen! I just can't find it... Its on a friend's mobo so there is not much hose and I've checked it al visually (as it's clear) but it does have several Ts which may have something in them. I'll just have to disconnect each one and check. Thanks for the idea

 

[Trident]

Do you have an in-line water filter e.g. Whale Aquasource in the feed? They can present a significant resistance to water flow. I tried the cheaper Pozzani equivalent that claims to be a direct replacement. Not so. The return spring on my galley foot pump is not strong enough to overcome to flow resistance of this type. Works fine with the Whale version though, so I have to pay three times the price for the genuine article.

Not on this boat - but good to know

 

[Daydream believer]

Do you have an in-line water filter e.g. Whale Aquasource in the feed? They can present a significant resistance to water flow. I tried the cheaper Pozzani equivalent that claims to be a direct replacement. Not so. The return spring on my galley foot pump is not strong enough to overcome to flow resistance of this type. Works fine with the Whale version though, so I have to pay three times the price for the genuine article.

I had a gauze filter & it seemed more of a point to attract bacteria so I discarded it. Do not really see the point with fresh water. It is not really like contaminated engine fuel is it.

 

[geem]

I had a gauze filter & it seemed more of a point to attract bacteria so I discarded it. Do not really see the point with fresh water. It is not really like contaminated engine fuel is it.

We run a guaze strainers to protect the pump. We also have a 1 micron filter in a 10" housing after the pump followed by a carbon filter, also in a 10" housing. None of this is enough to cause a pressure/flow problem even when filters are due for change.
If you drink from the tank as we do, it's nice to have sparkling clean water