Water tank partially emptying

[moonshadow]

I have had an interesting problem I am trying to resolve. My large, 100 gallon, fresh water tank is under the forward berth. When using this tank my pump will run and appears to act as though the tank is empty surprisingly early. Finally I measured the water to fill it and found it only needed 50 gallons. Surprisingly this matches what the Sheiber panels shows. When this last happened recently I explored with a small camera and confirmed that the tank was half full. The pickup tube seemed intact. The overflow valve is open. The pump screen is ok. Now If I use the other tank for a while I can switch back to the forward tank and use it again. Has anyone here had a similar issue?
Thanks, Paul

[Zanshin]

I have a slow leak from my water system that I have yet to locate. It is on the pressurized side and it triggers a short bilge pump drain about 4 times an hour. That little amount is enough to drain quite a bit of water from my tank, over time. Could that be happening - a slow drain into the bilge? You could try turning your bilge pumps off for a day and seeing how much (if any) water collects?

[moonshadow]

Thanks for the reply.
I have no water in bilge and the pump isn’t running. The tank is actually still half full when this happens. I confirmed that with my Camera endoscope as a dipstick with a view!

[Charlie-Bravo]

Does the aft tank suffer the same way, as in only half empties?

Thinking when the tank is full the pump has more weight of water to help the pump prime , a small hole or tear or leak in the pump diaphragm or valves could be spoiling the pump suction performance / prime when it has to pump up from half empty, giving the symptoms you describe.


Quite why running the other tank for a bit enables you to switch back to the fore tank I don’t know, does it then pump till empty?

I did a jabsco water pump re build article in a previous posting, it’s not difficult or a long job if that is what is needed.

CB

[DarknStormy]

Jan 20, 2023 17:06:43 GMT Charlie-Bravo said:

Does the aft tank suffer the same way, as in only half empties?

Thinking when the tank is full the pump has more weight of water to help the pump prime , a small hole or tear or leak in the pump diaphragm or valves could be spoiling the pump suction performance / prime when it has to pump up from half empty, giving the symptoms you describe.


Quite why running the other tank for a bit enables you to switch back to the fore tank I don’t know, does it then pump till empty?

I did a jabsco water pump re build article in a previous posting, it’s not difficult or a long job if that is what is needed.

CB

CB, sorry to hijack this thread but I've searched for the rebuild article and cannot seem to make my search foo work on it. Could I please get a link? 

Best, Michael

[Charlie-Bravo]

Hi, if you log on and click on my name you can view my ‘recent threads’ May 26 2022 and you will find it there, actually a jabsco bilge pump rebuild but is the same as my shower and water pumps.

CB

[ForGrinsToo]

Jan 20, 2023 11:27:47 GMT moonshadow said:

I have had an interesting problem I am trying to resolve. My large, 100 gallon, fresh water tank is under the forward berth. When using this tank my pump will run and appears to act as though the tank is empty surprisingly early. Finally I measured the water to fill it and found it only needed 50 gallons. Surprisingly this matches what the Sheiber panels shows. When this last happened recently I explored with a small camera and confirmed that the tank was half full. The pickup tube seemed intact. The overflow valve is open. The pump screen is ok. Now If I use the other tank for a while I can switch back to the forward tank and use it again. Has anyone here had a similar issue?
Thanks, Paul

I had a bad experience with the check valve between the water pump and the tank selector manifold. On (painful, awkward) disassembly, I found the check valve to be clogged with sizable pieces of plastic. The source seemed to be the interior of the manifold with black stuff flaking off. Granted, such a thing should affect all potable water as it is downstream from the selector valves. But it's worth checking all that plumbing, including the valves, I think.

Good luck,
Geoff

[moonshadow]

Thanks for the tips. Still investigating.

[rene460]

Hi Moonshadow, it is indeed a puzzling problem.  Usually pumps not pumping, and generally spurting and making noises means air in the system, as when the tank is empty.  Next most common cause seems to be a cracked inlet filter at the inlet to the pump.  Then occasionally pump issues or even blocked filter on the tap spouts.  The later causes would not generally have that very distinctive features of air in the system.  Generally with air in the pump, it still continues to run when the taps are closed, as it cannot generate the pressure as a compressor to trip the off switch.

Changing tanks appearing to fix the problem would suggest that the air is purged through in the changeover.  You would not expect changing the tanks to fix any pump issues other than air ingress.  So I would be looking for the tell tale air bubble under the filter cover, and looking for points where air might be leaking in possibly in the piping before the changeover valve.  But we need a little more information on whether changing the tanks over then back when the problem clears as already suggested.   Does this then allow you to empty the tank?

Is there any possibility that the issue coincides with weather conditions such as water use during a brisk sail with plenty of heel, or pitching that could intermittently allow air to enter the dip tube when the level is a bit lower.  Then curing by purging the air with water from the other tank would make sense.  And you would be able to empty the tank in more stable conditions.

rene460

[moonshadow]

Rene, I do think that your ideas are on track. I’ll keep trying to figure it out as I sail and move around. I do think that switching tanks for a bit then going back to original tank did fix the issue, so purging air might be the solution. I will try this again next time.
I did wonder if my vent was clogged and allowed negative pressure in the tank to build and cause the problem. But the tank showed no evidence of suction and the vent does allow overflow when filling. I don’t think my pump screen housing is the problem since it looks ok and only has an issue on one tank.

[SaltyDog]

From what you are describing I would guess that the air intake of the tank is clogged, so the pump draws a vacuum to its best of its abilities (not that much actually). If you remove the filler cap on a dry day, can you then empty the tank? If yes, your air intake is the problem.. If no, bummer! there must be something else the matter

[Moonshadow2]

Salty Dog, I have been thinking of the vent as a potential source of my problem also. The last time I ran my Watermaker I allowed a few minutes of overflow out of the vent, hoping that if it was blocked I could wash out whatever was there. I never saw anything come out of the vent except water. And my plan was to try opening the fill port if the problems persists. But so far the tank has emptied well past the level that was a problem. So perhaps solved? I’ll keep an eye on it and see. 

[moonshadow]

Well, as remarkable as it seems, this problem appears to be resolved without any major work on my part. After filling the tank with my Watermaker and allowing a few minutes of overflow via the vent I now have been able to use the whole tank. Must have been something plugging that up.
Again, thanks for all the ideas and advice. It’s a whole lot better than just relying on just my own ideas.