Jabsco diaghram FW pump rapid cycling

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Skipper

Skipper

.
Oct 9, 2008
1,742
Bristol 29.9 Dana Point
Have the Jabsco 36950-2000 fresh water pump with accumulator. Problem is that the pump now cycles rapidly on and off, instead of a steady hum, when using the water. Pressure is good for about 5 seconds when we use the faucets, but then slacks off due to the pump being unable to keep up because of its rapid cycling. Shuts down fine when the pressure builds back up.

I've purged the accumulator per the manual. Same result.

If I disconnect the output line and turn on the pump breaker, the pump happily shoots water into the bilge with no on\off cycling.

Could it be the switch? There is a small copper-colored disc in the switch, which (when removed) collapses between your fingers when you press it, and springs back when released. Could this disc just be too weak from years of use?
 
Jake N Eggs

Jake N Eggs

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Jun 2, 2011
347
Hunter H33 Port Credit Harbour, ON.
In general terms, pumps produce flow. If you restrict the flow it will build pressure. When the pressure builds the switch turns off the pump.

It could be the switch is stopping the pump at too low a pressure or it could be a blockage that is restricting the water flow.

Good luck.
 
ifmdalvey

ifmdalvey

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Feb 2, 2010
373
Island Packet 37 Hull #2 Harpswell Me
Or, you could have an air leak which will not allow pressure to build and therefore rapid cycling of the pump.
 
Johnb

Johnb

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Jan 22, 2008
1,457
Hunter 37-cutter Richmond CA
The accumulator needs to have air in so it can serve as a volume reservoir. You say you purged it but has it got that cushion of air in it. That might require opening a vent on top and bleeding water from the bottom.

This has to be repeated from time to time as the air dissolves or gets entrained into the water.
 
R

Ray Bowles

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Oct 6, 2008
857
Hunter, Island Packet, Catalina, San Juan 26,38,22,23 Kettle Falls, Washington
The tank on our boat was a bladder type. There was a rubber bladder inside the metal accumulator tank that held air pressure in the top end and then the water was in the bottom. It was about 2 1/2 to 3 gal total volumn and with the tank dry it required a certain amount of air to be pumped into the tank prior to the water pump being started. I think that charge was about 10 lbs. The water then pushed against that air bladder and at a certain pressure the pump turned off and the water would run until the water pressure dropped enough to start the pump. The air charge usually lasted a couple of years.
Ray
 
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bletso

bletso

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Aug 20, 2013
106
Globe 38 PCB
It could be a pump check valve. Kits are available. I have found that just looking at one you can't tell if they are bad.
 
Skipper

Skipper

.
Oct 9, 2008
1,742
Bristol 29.9 Dana Point
bletso said:
It could be a pump check valve. Kits are available. I have found that just looking at one you can't tell if they are bad.
Click to expand
Thank you. Yes, another poster mentioned a blockage too. If the built-in check valve is failing, it could restrict the flow enough that the downstream system backpressure momentarily trips the pressure switch. This would account for the normal flow when the pump discharge hose is disconnected.

That's 2 votes so far for flow restriction, so I'm guessing that this type of failure for the pressure switch is not as common.

I'll look at the valve this weekend. Thanks again.
 
Skipper

Skipper

.
Oct 9, 2008
1,742
Bristol 29.9 Dana Point
bletso said:
It could be a pump check valve. Kits are available. I have found that just looking at one you can't tell if they are bad.
Click to expand
:dance:

Check valve had a glump of silicone in it. 12 seconds with the thin needle-nose, then put it all back together, and the system is back to fabulous.

Cost: $0

Thank you
 
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