Water pump only works when water tank is full

[alirose]

We have a Manta catamaran 2000, the pump is a Sureflo Blaster 11, linked with a Flojet 2 gallon expansion (accumulator) tank. The galley water pump (and accumulator) work just fine until the 100 gallon water tank is less than 80-85% full. It seems as if air may be entering the system at that point, but I’m not sure how. It may also have something to do with the weight of the water forcing the pump to work until the water in the tank becomes lighter, really an uninformed guess. The symptoms - as and when the tank is below 80-85% full - the water pressure drops and the pump continues to run, even with the faucet off. The sound of the pump is a low dull growl as opposed to a full throated growl when it’s working properly. If I then re-open the faucet, pressure will eventually return, along with the full throated sound of the pump.
I did put a new water pump in (not so sure I needed one now), but still having the same problem. Any ideas would be welcome, we have spent a long time trying to problem solve.

[Dave852]

Originally Posted by alirose

We have a Manta catamaran 2000, the pump is a Sureflo Blaster 11, linked with a Flojet 2 gallon expansion (accumulator) tank. The galley water pump (and accumulator) work just fine until the 100 gallon water tank is less than 80-85% full. It seems as if air may be entering the system at that point, but I’m not sure how. It may also have something to do with the weight of the water forcing the pump to work until the water in the tank becomes lighter, really an uninformed guess. The symptoms - as and when the tank is below 80-85% full - the water pressure drops and the pump continues to run, even with the faucet off. The sound of the pump is a low dull growl as opposed to a full throated growl when it’s working properly. If I then re-open the faucet, pressure will eventually return, along with the full throated sound of the pump.

I did put a new water pump in (not so sure I needed one now), but still having the same problem. Any ideas would be welcome, we have spent a long time trying to problem solve.

If your gauge is correct and the tank in indeed 80% full then I would say the pickup tube has corroded to the point the tube in only 20% down into the tank or perhaps broke off at that point.

[alirose]

Thank you Dave,
We have been thinking along those lines too, and are trying to find out where the pick up line is in the tank - and where it exits - without tearing the boat apart. The Manta site has not yet come up with clues...

[jamhass]

If you can get an ear or stethoscope close to the tank, try disconnecting the inlet line to the pump and blowing air back into the tank, assuming there isn't a check valve in the system (otherwise, disconnect at the check valve.) If all is normal, you should be able to hear bubbling in the tank. If not, likely a dip tube failure.

If you hear bubbles, then your pump is not priming properly. Possible causes: air inleak at a fitting, leaking valves in the pump, pump too high relative to the tank.

Good luck

[rha9]

Don't know the age of your tanks, but I agree with the first post. In my case the water system worked properly until the tanks were about half full, then nothing. I pulled the one pickup (not easy) and it had corroded through about 12" down so the pump was pulling air at that point. I replaced both tank pickups with a plastic type (the previous ones looked to be copper?) about 10 years ago and have had not trouble since.

[alirose]

Thanks RHA9 and others who responded. Those of you who have had a similar issue and/or switched out pickup tubes, where is it located or more accurately, how do you access it? I'm attaching a photo of the top of our tank. The white marked line goes to the gauge sensor, the small black line is for the water maker infill, the line with hose clamps is yet to be explored.

[rha9]

Strange, that the pickup tube is not obvious. Typically it would be on the top somewhere. I would expect that the line with clamps is the tank input line, which should lead to a deck fill somewhere, although it could be the pick up line but I doubt it.

You should be able to trace back from the input to your freshwater system (pump location?) to find the access to the tank(s).

[JimsCAL]

Pickup could be low on one side of the tank. Mine is.

[Tellie]

The line with the hose clamps and the non collapsible hose is most likely the pick up not the fill line. It is not unusual for manufacturers not to have an access plate for your fresh water tanks. Looking at the picture you posted it looks like what you see is the only access to the fresh water tank. You may be looking at adding an inspection plate to your tank to gain access to the pick up line, a fairly easy project. I agree that there is probably a few pin holes in the pick up line right about at the 80-85% fill area and this is why your pump runs continuously as it loses it's prime until you open a faucet allowing for an easier flow of water. The boat probably sat for a good long while with the water level right there causing some corrosion at that mark. If your pick up line is corroding, and I'm assuming the pick up line is the same metal as the tank, I would really want a inspection port to visually see and inspect the inside condition of the tank itself.


PS the small black line is the watermaker tube to fill the tank.

[alirose]

The line with the clamps appears to be the input line which comes up under the galley sink. I'm not following why you think that would lead to the deck infill, which is at the back of the transom. Am I missing something? Additionally, that clamped line is rigid, feels brittle, and appears to be glued on to the grey welded pipe it's attached to. We are wary of taking/forcing it off unless there's a chance that the pickup is somehow accessible through that...Of course, the tank manufacturers, "Best" are nowhere to be found on the internet, presumably long out of business. Thanks again for your responses!

[alirose]

OK, in my clueless state, this is beginning to make more sense. The clamped hose is the output and comes in under the sink. To test my understanding, I think I'm deducing that the welded pipe the hose is clamped to is the pickup? If yes, how do we remove and replace? Apologies to the eye rollers, we are trying to learn and not knee jerk to professionals.

[Diesel Bill]

Depending on tank top thickness, might it be possible to drill and tap or J-B Weld a new fitting for a new suction right next to the clamped on suction hose and switch the hose over to the new fitting?

[Dave852]

You can remove the sender or the water maker fill fitting and stick one of those small cameras in the tank to have a look at the pickup tube. Your sight may be blocked by baffles. An access port to check the condition is a good idea but you have to know where the baffles are to place it properly. That tank is very shallow as it’s under the cockpit if I remember correctly.

[Dave852]

An Endoscope can be had for as little as $20, make sure it is semi-rigid so you can maneuver around inside the tank.

[hzcruiser]

Originally Posted by alirose

[...] work just fine until the 100 gallon water tank is less than 80-85% full.

[...]
If I then re-open the faucet, pressure will eventually return, along with the full throated sound of the pump.
I did put a new water pump in (not so sure I needed one now), but still having the same problem.

Hello Alirose,


first q: has this always been the case or is the symptom new? Or is it just a new-to-you boat and the PO (previous owner) didn't leave proper documentation behind? We tend to blame everything on the PO, for generations to come Otherwise it's the builders fault, of course.


The pump runs when the pressure sensor in the head of the pump measures a pressure below the set point (adjustable by the center bolt on the head).

You say the pump keeps running with the faucet off, which means either a leak on the pressure side (which doesn't seem likely) or air in the hose. What speaks against a broken pickup tube is that the water returns when you turn the faucet on. Is it sputtering air and water in that case? And after a few seconds it's a full stream again?

Either way it sounds as if the pump would be running all the time, faucet on or off?

Originally Posted by alirose

The line with the clamps appears to be the input line which comes up under the galley sink. I'm not following why you think that would lead to the deck infill, which is at the back of the transom. Am I missing something? Additionally, that clamped line is rigid, feels brittle, and appears to be glued on to the grey welded pipe it's attached to. We are wary of taking/forcing it off [...]

Are you sure about the input line? If it "comes up under the galley sink", it would have to go to your pump and accumulator first. Did you trace it properly?

Let's not forget that every tank needs a breather line in order to let air in when you draw the liquid out. Otherwise the tank would collapse with a loud bang (or it is a bladder).

That clamped-on line looks very much like the breather line which has to be at the top of the tank, without a pickup tube. It just runs upwards and has an open end, maybe with a little dust filter to prevent dust and insects to get in. It could also be the filler line with a breathing tube teed off.

If that line feels brittle, you should not be reluctant to take it off, but replace it straight away to prevent more problems down the road.


Which brings us to question 2: where does the deck infill hose end? How does the water get into the tank in the first place, apart from the watermaker line you mentioned?

Originally Posted by alirose

[...] The clamped hose is the output and comes in under the sink. To test my understanding, I think I'm deducing that the welded pipe the hose is clamped to is the pickup? If yes, how do we remove and replace? [...]

Boat plumbing is no rocket surgery, Alirose. To replace the hose, measure the OD of the output pipe on the tank (e.g. with some vernier calipers) and roughly estimate the length of that hose, get a new hose (suitable for drinking water) with that ID before ripping off the old one.

Open the hose clamps, slide them onto the hose, then heat up the old hose with a hair dryer or heat gun if it doesn't come off freely. You could also just cut the hose lengthwise two or three times along the length of the metal tube, then peeling off the hose should be very easy.
Clean the metal tube, lube it a bit with some silicone grease (or a hint of Vaseline or even cooking oil if you don't have the proper grease), slide the clamps on the new hose and slip it on the tube. Move the clamps in place, tighten them and you're done. If you want to do it "by the book", you would also replace the hose clamps with new, stainless steel ones.


Next, have a look at the bottom of the tank, if possible. There might be more hoses hidden there.