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Water Pressure Pump Thuds


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Hi There,

 

I have an annoying problem with my water pressure pump. After pressurising the system the pump turns off as expected. Every 60 seconds or so there is then a thud from the pump, this persists indefinitely. I have replaced the pump and all inlet pipework and the problem persists. This is a fairly recent issue that has appeared in the last few months. Boat is about 11 years old.

 

There is an accumulator tank fitted straight after the pump. I bled the valve for a second or two and there was no water coming out when the system was pressurised. I added a few pumps of air with a hand pump to account for any losses over the years.

 

I don't see how this can be a leak on the discharge side as that would imply that the pump is pressurising from 10 to 25 psi each thud which is definitely less than a second long.

 

Any ideas?

 

Thuds right at the end of the video.

 

https://drive.google.com/file/d/1AE4WXjhMttx3WvqnTrzIcb6pl4eTNd4Z/view?usp=drivesdk

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11 minutes ago, CheezyArmpit said:

There is an accumulator tank fitted straight after the pump. I bled the valve for a second or two and there was no water coming out when the system was pressurised. I added a few pumps of air with a hand pump to account for any losses over the years.

I don't know if I'm the only person reading this who has no idea what you mean by the above.

A typical accumulator doesn't have anything to bleed.

 

A few pumps of a hand pump could mean anything, and if you don't know what it was pressurised to in the first place, or how much you have increased it by, then it is impossible to predict the effect of what you have done.

 

However it will not be relevant to the problem you are having.

I suggest if there are no leaks in your system after the pump, the normal explanation might be that pressure was escaping back through the pump.  But you say you have replaced it, and it still happens.

I think it is possible you have a leak on your fresh water system that you have yet to discover.  Have you looked under the floors lately?

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18 minutes ago, CheezyArmpit said:

I don't see how this can be a leak on the discharge side as that would imply that the pump is pressurising from 10 to 25 psi each thud which is definitely less than a second long.

If you have managed to end up with your accumulator sufficiently depressurised that it is doing nothing, then the running time to go from 10 to 25 psi could well only be extremely short, as there is nothing in the system that will compress.

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5 minutes ago, alan_fincher said:

I don't know if I'm the only person reading this who has no idea what you mean by the above.

A typical accumulator doesn't have anything to bleed.

It's an accumulator with a rubber membrane. Air on one side, water on the other. If water comes out when you depress the pin on the air valve, the membrane is split.

 

The problem was present before and after I pumped the accumulator up, so I think you're right -- likely unrelated.

 

5 minutes ago, alan_fincher said:

I think it is possible you have a leak on your fresh water system that you have yet to discover.  Have you looked under the floors lately?

 

The original pump was leaky around the filter, which is why I replaced it. There was a lot of water under the floors! The chipboard underneath the pump was absolutely sodden.

4 minutes ago, alan_fincher said:

If you have managed to end up with your accumulator sufficiently depressurised that it is doing nothing, then the running time to go from 10 to 25 psi could well only be extremely short, as there is nothing in the system that will compress.

I don't think that's the issue -- I get a decent run time on the taps when the pump is shut off. The pump continues to run some time after the taps are shut off too.

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If the pump is burping occasionally then there is a leak which is allowing the system to depressurise. Either it’s passing by the pump backwards or it’s dripping from somewhere within the boat (or past the PRV). It’s unlikely to be the pump as you’ve replaced it, therefore you have a small leak downstream somewhere. 

 

A short-term fix is to turn the pump off when it’s not required. 

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To proove whether or not there's a leak on the high pressure side remove the pipe or hose from the outlet port of the pump and cap it off securely or on the pipe or hose as close to the pump as possible. If the pump then stops burping you have a leak.

  • Greenie 1
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1 minute ago, bizzard said:

To proove whether or not there's a leak on the high pressure side remove the pipe or hose from the outlet port of the pump and cap it off securely or on the pipe or hose as close to the pump as possible. If the pump then stops burping you have a leak.

Good tip :)

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If your system is fitted with a check valve then it is possible for the accumulator to work perfectly and if you have a leak, internal or externally then it is possible for the length of pipe between the check valve  and the pump to depressurise and a table spoon full of water would be more than enough to recharge it.

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When we replaced a continually slowly dripping PRV with a new one, we aquired a thump problem accompanied by a breif discharge from the PRV port. At the next chandlery a person with exactly the same problem (and the same pump) was purchasing a new water pump of a different brand "because their near new existing pump was worse then the one it replaced". Fortunately the boatyard that performed our next service showed me where the pressure adjusting screw on the pump was located (the operating manual had no mention of pressure adjustment) The screw is on the end of the pump body under a cover. Turning it one way makes the problem worse but the other cures it when the pump discharge pressure drops sufficiently below the PRV preset pressure. The pump and PRV gave no further problems in five years. We did not have an accumulator. The pump would run for a second or so every three hours or so, any more frequent running would indicate a leak, dripping tap, or the PRV valve needing a reset by turning the red knob.

Edited by DandV
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