Water pump only works when water tank is full

[alirose]

An interesting development. We have discovered through random acts of diagnosis that the pump will work when the water is below the critical 80% tank level if we dry prime the pump. It will then work flawlessly, with the odd aberration back to puttering out and not turning off, but this will again be rectified by another dry prime of the pump. This seems to suggest that the. problem is not a corroded pickup (which we are not convinced we have yet found) but how is the perfect functioning at 80% or above explained. Yes, hzcruiser, first order of today is to switch out the filler hose - we have confirmed that the clamped hose in the photo is the filler - but perhaps need to be back looking at the pump and expansion tank?

I'm impressed by the thoughtfulness of responses, the willingness of people to take time to help, and the absence of critique of our inexperience. Thank you everyone!

[alirose]

BTW, I'm using "filler hose" to refer to the hose that is clamped in the picture, and it leads underneath the cockpit to the galley. It then goes through a filter before feeding the pump and accumulator, with a T after the filter to also feed the foot pump. The deck fill is on the back of the transom.

[hzcruiser]

Originally Posted by alirose

[...]
I'm impressed by the thoughtfulness of responses, the willingness of people to take time to help, and the absence of critique of our inexperience. Thank you everyone!

Rather unusual, indeed ;-)
I'm not sure what you mean by "dry priming" the pump? Just leaving it running without water?

The deck fill is on the back of the transom.

Ok, but where is the other end of that hose, one wonders? And you still need a breather line somewhere.

[Tellie]

Again, the non collapsible hose IS your pick up line. That brand of NON-collapsible hose is very stiff. It would not be all that unusual to see a bit of air ingress into that end of the hose or the other. That hose needs to be slightly heated until pliable to easily get on and off the fittings. Clamping it down while still warm makes for a better seal. Trying to clamp down this type of hose cold and preventing air ingress is very difficult without very good clamps and a lot of pressure with a nut driver not a flat head screw driver. You need a good visual of the interior of your tank. Get an inspection plate installed. This will help in future cleanings as well.

[alirose]

By dry priming I mean we turn the pump off when it's lost full pressure, then run the faucet we're using dry, close it, then turn the pump back on and the pump primes perfectly. Our pump is a Shuflo and is designed to be able to dry prime.

The deck fill on the transom is a molded metal part of the tank with a cap. There is a breather vent next to it, also on the transom, two little nostrils...

Thanks again!

[alirose]

Thanks. Can you describe the pickup line? We understand how to remove and replace the hose attached to it, but no knowledge of the design of this pickup. I'm imagining the metal spout the clamped hose attaches to is a fixed pipe running down to the bottom of the tank. No google, technician, or other forums thus far have been able to answer this question.

[Pete17C]

Is the bladder in the expansion tank shot?

The pump should run until it pressurizes the expansion tank, then shut off. After drawing some water from a faucet slowly the pump should kick in and run, and shut off/on intermittently as it brings the tank to pressure (off) and then after going low pressure as you run the water (on) again.

[chouliha]

It does sound like it might be the pump. How old is the pump? Have you tried swapping it out with a new one? Just a thought.........

[Tellie]

Originally Posted by alirose

Thanks. Can you describe the pickup line? We understand how to remove and replace the hose attached to it, but no knowledge of the design of this pickup. I'm imagining the metal spout the clamped hose attaches to is a fixed pipe running down to the bottom of the tank. No google, technician, or other forums thus far have been able to answer this question.

Correct, it's just a metal tube welded to the underside of the 90 degree metal fitting the non collapsible hose is attached to. This tube goes from the 90 degree fitting down to the bottom of the tank where it picks up the water the pump is drawing from. This is why the other end of the non collapsible hose feeds the input side of your pump under the galley sink. This is why I recommend you carefully check both ends of the non collapsible hose by gently heating them, removing them, cut back an inch or so on each end, re-heat them, and re-attach with good clamps. The reason they used a non collapsible hose here is because your water pump creates a vacuum which will over time collapse a standard braided hose pinching off the supply to your pump greatly reducing flow. And I still say an inspection plate is in order. If you do have pin holes in the pick up line you may very well have other concerns with metal corrosion of the inside walls of your tank that an inspection plate will allow you to see. The pick up line may be a thinner metal than your tank walls and will get pin holes faster but it is an early warning sign.

[alirose]

Thanks Tellie, thanks everyone, it's all making more sense. A steep learning curve, good for neuroplasticity at my age...

[jamhass]

Are you sure the black hose with clamps is the feed line. I would expect it to be the vent.

[Tellie]

Originally Posted by jamhass

Are you sure the black hose with clamps is the feed line. I would expect it to be the vent.

What leads me to know this is the pick up line is first ailrose's #17 post where he states "BTW, I'm using "filler hose" to refer to the hose that is clamped in the picture, and it leads underneath the cockpit to the galley. It then goes through a filter before feeding the pump and accumulator, with a T after the filter to also feed the foot pump." and second this is a very small diameter pipe and hose. Compared to the small black 1/4" tubing and fitting just above it which I use as a visual comparison this would be far more likely to be the pick up. Air vents on fresh water tanks, though not written in stone, are usually 5/8" or larger. If this were the air vent and it was plumbed to the input side of his feed pump as he describes then the pump would not work at all as there would be no pick up tube on the air vent.


One thing I did not consider as to a possible air ingress problem is the foot pump that is "T"eed into the pick up line. This can certainly be a point of air ingress as well, either those fittings or the from the foot pump itself.


As long as we are picking things apart there are two other things I see in the original picture that would be somewhat of concern. 1) I would change the two fittings on the sending wires to proper fittings. These two fittings and connections are begging for moisture weeping and a failure point for the sending unit. 2) This one I see on a lot on boats. The improper use of double clamps. If you look carefully at the picture you will see the second clamp is just past the end of the metal 90 degree fitting the hose is clamped to. It's a bit tough to see, but the non-collaspable hose is clear and you can see the fitting does not go past the second clamp. This leads to more hose failures on fittings than anything else. If the fitting is not long enough to use two clamps then one is better than two.

[hzcruiser]

Originally Posted by Tellie

[...]

2) This one I see on a lot on boats. The improper use of double clamps. If you look carefully at the picture you will see the second clamp is just past the end of the metal 90 degree fitting the hose is clamped to. It's a bit tough to see, but the non-collaspable hose is clear and you can see the fitting does not go past the second clamp. This leads to more hose failures on fittings than anything else. If the fitting is not long enough to use two clamps then one is better than two.

Not sure about that, as the right clamp looks the same size or diameter as the left one. One had to be rather daft to put a clamp on a hose where there is no support on the "inside".
But either way, since this is not a clamp on a through-hull the second one is not really required.

[alirose]

Tellie, thanks again!
What would be a proper fitting for the sending unit? I like your observation.
Secondly, the hose from the T to the foot pump is chronically flattened, suggesting it's chronically suctioned. Would that not suggest there is no air ingress? Happy to be wrong as that's an easier fix than the pickup which we've had confirmed is welded into the tank. Do you have a hunch about the pickup given we can make the pump work below the 80% water line by futzing as described earlier?

[hzcruiser]

Originally Posted by alirose

[...]
Secondly, the hose from the T to the foot pump is chronically flattened, suggesting it's chronically suctioned. [...]

Interesting tidbit! So does the foot pump work in both cases?
It might be time to properly locate the issue by testing each piece along the line, e.g. using some spare hose and that old pump directly on the tank outlet, if that works, move it further up the "water chain" and so on.