Water Pump loses prime when water tank level is 1/3 full

[RKW]

My water pump loses prime when the water tank level is showing 1/3 full. If I add more water to the tank (1/2 full or better) the pump will re-prime. It seems like a open and shut case of needing to change out the water pump, but before I do that I thought I'd ask for opinions before I go forward.

Thoughts? Thanks in advance.

[jseyfert3]

SoundGuy wrote:

Have you considered fresh water tank sag?



Obviously if the pump's intake hose doesn't draw from the lowest part of the tank the pump it can't pump that water. I had this problem with our Freedom Express and installed braces to support the tank and ensure the bottom was flat. I also moved the draw tube which was connected to a side port on the tank to the tank drain port which was on the bottom of the tank. Solved the problem entirely. :B

Wow, that's crazy they put that tank in there with no supports. The tank on ours is supported along both long sides with L-brackets, and has two cross bars between these side brackets to prevent sag. And the water pump draw tube was put on the bottom of the tank.

I guess we got lucky. With those two things we can drain our tank dry with the pump, provided we park the camper level.

[Hondavalk]

SoundGuy, what a great easy solution. Thanks

[RKW]

profdant139 wrote:
RKW, what I want to know is this -- how did you get your pump to empty your tank completely so that only a little dribbled out?? Is the outflow tube mounted on the lowest point of the tank? If so, congratulations!

Ours was not, so we had it re-installed at the low point. And I put in supports, like SoundGuy did, to combat the dreaded "saggy belly" phenomenon. (Too bad it only works on RVs and not on humans.) . 😉

Well it did dribble for the best part of a half hour, so I suppose some water remained.

The only part of my tank I can see is the drain. It's enclosed and has a heater that can be turned on when needed.

[profdant139]

RKW, what I want to know is this -- how did you get your pump to empty your tank completely so that only a little dribbled out?? Is the outflow tube mounted on the lowest point of the tank? If so, congratulations!

Ours was not, so we had it re-installed at the low point. And I put in supports, like SoundGuy did, to combat the dreaded "saggy belly" phenomenon. (Too bad it only works on RVs and not on humans.) . 😉

[RKW]

Thanks to everyone for the replies. Here's the deal. Based on your suggestions, with the tank level indicating 1/3 full, and the pump in an unprimed state, I opened the drain valve on the tank and it dribbled out. I didn't catch it in a bucket and measure it because it was such a meager amount that it was apparent that the tank was essentially empty. It stopped dribbling out after about 20 minutes, leaving no appreciable amount of water on the ground. Bad level indicator.

I guess my problem changed from a bad pump to a bad water tank level indicator, which is a bummer because I always found the freshwater indicator much more useful than the greywater and blackwater indicators.

[JRscooby]

Another possibility is a leak in the intake line at about the level of the water when pump looses prime.
When I hear pump loose prime, I think of pump running, pumping, until turn/cycle off. When next comes on, no water. Put enough water in tank for it to prime, run without shutting off. Does it at some point start putting bubbles in the stream? If not, then it is likely a small leak that is letting air in, that allows water in line drain back to the tank. If water level is at or above the level of leak, water stays in line.

[wa8yxm]

Since the pumps are "Self Priming" you have one of two issues.
1: an air leak (it's sucking air)
2: a bad pump or bad pump check valve.

[SoundGuy]

RKW wrote:
My water pump loses prime when the water tank level is showing 1/3 full.

Thoughts?

Have you considered fresh water tank sag?



Obviously if the pump's intake hose doesn't draw from the lowest part of the tank the pump it can't pump that water. I had this problem with our Freedom Express and installed braces to support the tank and ensure the bottom was flat. I also moved the draw tube which was connected to a side port on the tank to the tank drain port which was on the bottom of the tank. Solved the problem entirely. :B

[KMLsquared]

My buddy has a Wildwood that is having this exact same problem. Water starts getting lots of air in it then wont pump at all. Pulls dump valve on the bottom and a ton of water comes out. Camping wold told him its fine and nothing is wrong. Following along to find out what you find.

[2oldman]

DutchmenSport wrote:
It's actually almost empty. The sensors are misreading.

This.

[Lynnmor]

First, the gauge is not very reliable. Next, the pickup port (a threaded hole) on many trailers is well above the tank bottom, so the pump will suck air at the top edge of that hole. Do what Dutchman said and measure the remaining water, I'll bet it is quite a bit. Now to fix the problem, connect the supply hose to the drain port on the bottom with a tee and plug the original.

[DutchmenSport]

I would not count on those sensor readings. Here's what you can try to do.

Use the water in the camper until the pump stops pumping water. Then put a bucket under the fresh tank drain and drain the water, catching in the bucket one at a time and dumping the bucket after each fill. Keep doing this until the tank is truly empty. Multiply the size of the bucket (gallons) by the number of dumps and then you know exactly how much truly remains once the pump starts sucking air.

I think you will probably find, not much. It's actually almost empty. The sensors are miss-reading.

Anyway, if another 15 or 20 gallon is dumped after that, and the pump is sucking air, then perhaps the end of the pipe in the tank is not actually at the bottom. It could have been stuck in too far, its curled upward instead of downward. Or maybe it wasn't stuck in far enough to reach the bottom. Once the tank reached the level of the end of the hose-pipe in the tank, regardless of what's left it will suck only air.

Doing this, at least you'd know for sure how much water is truly left in the tank once the pump quits pumping water. Before fiddling with the pump, I'd then try readjusting the depth of the pipe inside the tank.

[RLS7201]

You could install a new valve/diaphragm kit for less $$.

Richard