Water Pressure Pump ‘flickering/pulsing’ for a few seconds before switching off

[Peterlewis321]

I replaced my Jabsco Par Max 4 pump a few weeks ago (it failed) and had no choice but to go with a Johnson WPS 3.5 (as that was all the chandlery had) which I must confess seems pretty damn good and much quieter than my previous pump. We also have an accumulator fitted as part of the system and I set the internal pressure just below the cut-in pressure of the pump.
However, I’ve noticed that the pump seems to flicker on/off for maybe a few seconds when it repressurizes the system after a tap has been switched on and subsequently switched off. The only reason I know this is I can see the water pump light on the control panel in the saloon flicker for a few seconds between being fully “on’ and finally going out. I’ve bled the system of air (I think) and to be honest it is causing us no real issues as such, however I just wondered any opinion from this forum-not worth worrying about? Or does it indicate I have something setup wrong? Thanks

 

[3571]

I replaced my Jabsco Par Max 4 pump a few weeks ago (it failed) and had no choice but to go with a Johnson WPS 3.5 (as that was all the chandlery had) which I must confess seems pretty damn good and much quieter than my previous pump. We also have an accumulator fitted as part of the system and I set the internal pressure just below the cut-in pressure of the pump.
However, I’ve noticed that the pump seems to flicker on/off for maybe a few seconds when it repressurizes the system after a tap has been switched on and subsequently switched off. The only reason I know this is I can see the water pump light on the control panel in the saloon flicker for a few seconds between being fully “on’ and finally going out. I’ve bled the system of air (I think) and to be honest it is causing us no real issues as such, however I just wondered any opinion from this forum-not worth worrying about? Or does it indicate I have something setup wrong? Thanks

I used to use the bigger Jabsco water sets on fishing vessels, if the accumulator tank needed pressurised (with a foot pump) or the membrane inside had burst, it caused the pump to constantly cycle (rather than the occasional smooth on then off once the accumulator tank was back up to pressure) when you opened a tap or used the shower - the first sign was always the water out of the taps pulsing rather than flowing smoothly.

 

[henryf]

Reading the original post I didn’t get the sense that it was an accumulator problem. I felt the accumulator was providing water for a while before the pump kicked in but as the pump pressured the system up after the taps were closed it flickered a bit rather than shutting off cleanly.

Make sure you have sufficient voltage and current at the pump. Check for leaks on the inlet side of the pump particularly around the hard plastic pre filter. Air in the system would certainly cause a delay in the pump shutting off due to air compressing but water not compressing.

Other that the flutter at shut off is everything else good, ie. Water flows for a while when you turn a tap on before pump cuts in, no surging of water as the pump runs ?

 

[Peterlewis321]

Reading the original post I didn’t get the sense that it was an accumulator problem. I felt the accumulator was providing water for a while before the pump kicked in but as the pump pressured the system up after the taps were closed it flickered a bit rather than shutting off cleanly.

Make sure you have sufficient voltage and current at the pump. Check for leaks on the inlet side of the pump particularly around the hard plastic pre filter. Air in the system would certainly cause a delay in the pump shutting off due to air compressing but water not compressing.

Other that the flutter at shut off is everything else good, ie. Water flows for a while when you turn a tap on before pump cuts in, no surging of water as the pump runs ?

Yes spot on-the accumulator is all fine and what you said explained it much better than I did!! The water runs just fine, no surging or spluttering at all.
Funny enough I did notice the Jabsco in-line strainer (located in the pipe before the pump) seems to have an air bubble in it (but I thought maybe that is normal?) and I wondered if there might be air getting into the feed from the tank….I will check the strainer for leaks, as well as (best I can) the pipe run between the tank and the pump itself.

 

[superheat6k]

I would try increasing the pressure in the accumulator a small amount so it is set at or just above the pump kick in level, not below it. If the trigger pressure is very close to the accumulator minimum pressure it could literally be the rubber membrane bouncing (hysteresis) as the pump goes off, the pressure momentarily drops back below trigger level and the pump re-starts, until after a few 'flicks' the pressure stabilises. Increasing the pressure difference will allow for the hysteresis in the accumulator bladder to absorb the pump off pressure flick.

Many accumulators do not have a bladder so simply work by the water pressure squeezing the air trapped in the accumulator. On this basis the accumulator is always at pumped pressure, with the cut in / cut out controlled by the operating differential of the pump control switch. The accumulator can never be lower than the pump.

 

[Peterlewis321]

Yes spot on-the accumulator is all fine and what you said explained it much better than I did!! The water runs just fine, no surging or spluttering at all.
Funny enough I did notice the Jabsco in-line strainer (located in the pipe before the pump) seems to have an air bubble in it (but I thought maybe that is normal?) and I wondered if there might be air getting into the feed from the tank….I will check the strainer for leaks, as well as (best I can) the pipe run between the tank and the pump itself.

Thanks very much for the advice-will give that a go.