freshwater pump maddening problem

[BillHoughton]

The freshwater pump in our RV (2007 Itasca Navion) stopped holding pressure - it would run up to pressure, stop, then cycle every 15-20 seconds (estimated; never timed on the old pump). Based on advice here and at Winnebago, I bought a new pump and installed it; the problem recurred.

A very helpful customer service guy at Winnebago told me how to pressure test the system and stated that, if the system held pressure, the pump was defective. It held 90 pounds of air pressure for four minutes, so I ordered a second pump on the assumption that the first one was defective.

Same (bad word) problem with the newest pump, even after I ran all the fixtures to get the air out of the lines. Checked all kinds of stuff: opened water heater pressure relief valve in case there was air trapped (no), tested the check valve on the inlet to the water tank; removed the kitchen sink faucet aerator to confirm that I was getting water with no air in it; and so on.

A tech at Pentair/Shurflo, the pump manufacturer, suggests that I fiddle with the check valve setting, which I'll do tomorrow.

Another tech at Winnebago told the tech I've been working with that the check valve in the water heater could be seeping internally and creating the problem, although I don't see how that would make a difference (in a closed, pressurized system, pressure is equal everywhere). I can replace it without taking out the water heater, but I'd have to drain the water tanks (fresh water, water heater) and blow out the lines to avoid dripping on electronic parts (smart move, Winnebago!); but, again, I can't understand how it would make a difference.

Any other thoughts?

[OldTioga9]

Make sure that both "low point" drain valves are shut off completely to allow water lines to pressurize fully. Otherwise pump will cycle on and off. Ours are hard to get at and hard to turn off completely.

[Ray_IN]

A few drops of cooking oil lubricates plastic valves.

[Ray_IN]

A few drops of cooking oil will  lubricate the plastic valves.

[dougrainer]

I am not familiar with your model. BUT, I have 45 years as an RV tech.  MY FIRST impression when a customer has your problem and there are NO leaks on the ground or in the RV, is indeed a possible pump, especially over 15 years old. BUT, do you have a City water, water tank fill valve? Most RV's (motorhomes) do. The 2nd option I look at when your problem happens is the City water tank fill valve is leaking internally and the pump is just cycling and putting water back into the tank. Shurflo builds an excellent Pump, The odds are to get a new pump with the same problem is extremely rare. 

[MNtundraRet]

Sometimes there can be a loose connection in the shower wall. Have you gone outside to see if anything is leaking on the ground under the motorhome. 

[RayIN]

Pressuring the pump with 90# of air pressure is beyond its design limits, which likely damaged the pump diaphragms and seals.

The usual cause of pump cycling is a water leak somewhere, and the reply suggesting the commode water valve leaking is valid. Have you check that out and eliminated as a possible source?

[Krusty]

Internal leakage in the toilet? Is there a shut-off valve on the toilet you could use to isolate it from the rest of the system?

[ScottG]

Bordercollie wrote:
The low point drains on our 2004 Tioga 26Q are hard to access and hard to shut off , if not shut off completely, pump will cycle.

That's not what I meant. I meant if his low point drains have threaded caps instead of valves, use one of those caps on the output connection of the pump. Then turn the pump on to see if the pump holds pressure. This will take all the plumbing out of the equation except the pump. If the pump still cycles when it's capped, the pump is bad. If not, the leak is elsewhere.

[YC_1]

I have had to use a garden hose on the low point drain a couple of times to get all of the air out of the inlet side of the pump. The pump sucks on the inlet side where an air bubble remained. Air compresses, water does not. After the pump stops the air pocket under suction seems to pull back through the pump and the pump recycles. And this has happened with brand new pumps.

[Bordercollie]

The low point drains on our 2004 Tioga 26Q are hard to access and hard to shut off , if not shut off completely, pump will cycle.

[ScottG]

To make checking your pump even easier, do you by chance have caps on your low point drains? If so, use one of them on the output of your pump to test it.

[BillHoughton]

Continuing to be stumped. The cycling time is now down to three seconds! The parts house refuses to consider that the pump might be defective.

Has anyone had any experience with a company named USA Adventure Gear? They have a pump, comparable in price to what I paid for the Shurflo, with a lifetime warranty: this one here.. Says it's compatible - implied bolt-in compatible - with the Shurflo.

Still some more tests to run, but no sunshine on this project yet. Damitol - I've got so many OTHER things I want to do.

[RayIN]

That webpage states 2-yr warranty for the 3200 model, despite the advertising stating lifetime warranty. What's up with that???.

https://www.usaadventuregear.com/products/progear-3200-rv-water-pump-lifetime-warranty-high-pressure...

[ScottG]

BillHoughton wrote:

Is it feasible to install a check valve upstream from the pump and not rely on the pump's check valve?

Yes, you could use a Sharkbite check valve but the pump could still bypass internally and cycle.
In my experience it's very rare for a pump to leak internally. It happens but not that often. When it has happened to me I just disassemble the pump, rinse all its parts off and put it back together to fix it.
I would find a short piece of pipe and install it on the output of the pump. Plug the other end of that pipe and run the pump. That will tell you for sure if the pump is to blame.

How "West" are you? I'm in the Seattle area and have what you need to do this test.