Only access 1/2 of fresh water tank?

[sanjuan895]

I was pumping water out of my fresh water tank and noticed that the water pump really started struggling after pumping out around ~20 gallons. I checked the gauge mounted on the tank and it shows 1/2 full.

Has anyone else had a problem getting the fresh water tank to fully pump out?

[garrettw]

You probably have plastic shavings or other debris in the screen pre filter or check valve before the pump.

[Charlie-Bravo]

As well as the above diagnosis, you might check the tank vent / overflow, as you could well be pulling a partial vacuum if air can’t replace the missing water, this would fit the symptoms.
You could remove the tank inspection hatch, usually a screw off item, or the deck fill cap, and then see if that allows a full pump out, and if this is the case, the vent needs cleaning out / unblocking.

Connecting a dinghy pump to the vent pipe and giving it a good ‘stomp’ sometimes clears a blockage.

CB

[sanjuan895]

Thanks for the suggestions. I’ll check and report back

[rene460]

Hi Sanjuan,

While you are investigating, it is worth carefully checking the filter cover on the inlet side of the pump for any sign of an air bubble.

Those covers have a reputation for developing a crack.  With a full tank, the water level is enough above the filter that the pressure in the filter is above atmospheric and it all works though may leak the odd drip of water.  Leave a dry tissue under the filter and you may detect it.

However, when the water level in the tank drops the inlet pressure at the filter falls with the level, and may allow air to leak into the filter.  The water pump will not pump air so the typical empty tank pump noises occur.   You can easily see the air bubble inside the filter cover - there should not be any air bubble.  There are many threads in the archives on this, you are certainly not alone.  On my SO30i, the filter was about the mid hight of the tank, the cover did develop a crack, and we had the problem you described, so another thing worth checking.

Unfortunately several of us have found that you can’t buy a replacement cover alone, which is a pity, as the lower half of the filter housing seems to be ok, but a new filter solves the problem.

I don’t like to recommend glue to repair the cover as it is dealing with your drinking water.  However, if you can see a crack, it may be worth trying electrical tape or similar on the outside, which may give you a bit of relief while you source a new cover.

rene460

[zaphod]

Aug 15, 2023 10:07:41 GMT rene460 said:

Hi Sanjuan,

While you are investigating, it is worth carefully checking the filter cover on the inlet side of the pump for any sign of an air bubble.

Those covers have a reputation for developing a crack.  With a full tank, the water level is enough above the filter that the pressure in the filter is above atmospheric and it all works though may leak the odd drip of water.  Leave a dry tissue under the filter and you may detect it.

However, when the water level in the tank drops the inlet pressure at the filter falls with the level, and may allow air to leak into the filter.  The water pump will not pump air so the typical empty tank pump noises occur.   You can easily see the air bubble inside the filter cover - there should not be any air bubble.  There are many threads in the archives on this, you are certainly not alone.  On my SO30i, the filter was about the mid hight of the tank, the cover did develop a crack, and we had the problem you described, so another thing worth checking.

Unfortunately several of us have found that you can’t buy a replacement cover alone, which is a pity, as the lower half of the filter housing seems to be ok, but a new filter solves the problem.

I don’t like to recommend glue to repair the cover as it is dealing with your drinking water.  However, if you can see a crack, it may be worth trying electrical tape or similar on the outside, which may give you a bit of relief while you source a new cover.

rene460

I had a cracked strainer cover like you describe. When that happens the pump sucks air and behaves like the tank is empty, with the pump running continuously and unloaded.

What the OP is describing is that the pump is laboring rather than unloading.

My money is on a plugged vent. It sounds like the tank is going into negative pressure.

[sanjuan895]

Both vent and filter(and cap) appear fine. I don’t see any leaks coming from the filter, and I cleaned it out just to be sure it wasn’t getting clogged by debris. With the hose off the tank vent I can feel some suction when the pump is running, and air can move freely from the vent hose to the vent. The filter has a little to no air in it when the tank is over half full, but starts emptying out when I get to half a tank.