Lessons Learned on FW Pump Priming

[mfa]

This week I was using my onboard water pump to supplement the water pressure at an RV park that had low park pressure. I wasn't paying attention to how much of my own FW I was using and the FW tank ran dry in less than a day.

After refilling the tank, I turned my pump back on and it ran continuously -- it would not prime. It took me about an hour to find where the pump was hidden. It was behind a screwed-down panel under the kitchen sink.

I sat there and looked at the pump with my brain out-of-gear, wondering what the trick was to get it to prime. I noticed there were some blue finger-grip things on either side of the pump that I thought were valves. Perhaps operating one of these was the key?

Here is where I learned a very key lesson the hard way -- NEVER OPERATE ANYTHING WITHOUT KNOWING WHAT THAT THING IS GOING TO DO. I pulled one of the blue things out to the side and water started SPEWING out of it. Worst of all, I couldn't get it to go back in and stop, even with the pump turned off. Paniced, I ran out the door, around the RV, and cut off the park water supply. By then, the water is out from under the cabinets, standing about a quarter-inch deep on the vinyl flooring, and seeping into the bordering carpeting.

Long story short -- what I pulled out was a quick-disconnect for the piping on the high-pressure side of the pump. When I finally realized what it was and how it worked, I still couldn't get it back together without it dripping under pressure. I think I must have slightly dinged the o-ring seal in my earlier panic. I ended up swapping it with the o-ring on the low-pressure side, and it did finally seal.

At least by that time I had managed to salvage our trip. For the previous hour it looked like we were going to have to pack up and head for home.

As I sat there looking at the pump and the mess, my brain finally engaged and I saw what should have been obvious. The pump cannot prime itself by pumping air from the dry inlet against the park pressure on the other side of the pump. I cut the park supply, opened a faucet, and then turned the pump on. It primed in less than 15 seconds.

[GStream40]

You should never run the water pump at the same time as being hooked up to city water. There is a check valve in the pump that you will get water from the higher pressure source. Which in your case was the pump, that is why the tank was emptied.

If the city water pressure is too low for your needs, then fill the water tank and use the pump with the city water shut off. Then fill your tank as needed.

Ron

[mfa]

It's a simple pump system on my MH. One inlet and one outlet. When the pressure drops below a certain level, the pump pulls from the suction side (line from the FW tank) and pushes to the discharge side (line into the pressurized side.)

There's a check-valve in the pump to keep the water on the pressurized side from flowing into the unpressurized side. There is also a check-valve elsewhere to keep the MH pressurized water from back-flowing into the city water.

IMO, I can't see that it make any difference whether you have the city water on or off in a low pressure situation. Either way, you are going to drain water from the FW tank as-required. Leaving the city water on give you the option of turning the pump switch off and using the city water at a low flow rate for times when you don't need as much pressure, such as hand washing and teeth brushing.

[GStream40]

You really answered your own question as to why I don't and won't in the statement:

"As I sat there looking at the pump and the mess, my brain finally engaged and I saw what should have been obvious. The pump cannot prime itself by pumping air from the dry inlet against the park pressure on the other side of the pump. I cut the park supply, opened a faucet, and then turned the pump on. It primed in less than 15 seconds."

The water pump is fighting against the park pressure be it low, but still fighting against it.

One thing I have found with some pressure regulators that we install inline with the hose from the park supply is when the park pressure is low and a regulator is not really needed, some regulators will cut down the flow of the park supply to the coach. In these cases, if one removes the regulator, the flow increases. You might want to try that to see if it helps with your water supply problem with the park water.

BUT do not run your pump with the pressure regulator removed since it actually is a check valve in sense that it will not allow your pump water to flow back into the park supply unless you also have a back flow preventer also installed in the line or the park does at their valve connection.

Ron

[Bill Reetz]

GStream40 - thanks for the above post. Ran the water tank dry last weekend, filled it up then tried to get water using the pump - nada not even a wimper. Then I remembered your post, shut off the city water, opened the kitchen faucet and turned on the pump BRAAK and I had water again!

Thanks

[mfa]

...I cut the park supply, opened a faucet, and then turned the pump on. It primed in less than 15 seconds.

GStream40 - thanks for the above post. Ran the water tank dry last weekend, filled it up then tried to get water using the pump - nada not even a wimper. Then I remembered your post, shut off the city water, opened the kitchen faucet and turned on the pump BRAAK and I had water again!
Thanks

You're welcome. :wink:

[2007 Kingsport]

I had a similar problem with the water pump in my 2007 Kingsport. Yesterday the campground I was at had an overnight freeze warning, so the city was shut off. Before they secured the water, I filled my onboard tank and then disconnected the city water.
When I turned on my pump, it just ran and ran. I tried opening a water valve to purge any air from the line (tried opening all of the valve actually) and still didn't have any luck.
I found the pump (located under the lower bunk in the rear) and disconnected the outlet side while it was running. Only a small trickle of water came out.
Then I disconnected the input side (with the pump off) and had a brief period of minor flooding (nothing major). Put the input and output back on and tried the pump again. Pump just ran and ran. No water at any of the faucets.
In my frustration :evil:, I smacked the pump a few times and suddenly I had water pressure. :D
Is there a proper way that I should be priming the pump? This is the first time that I have been without campground water, and the owner's manual doesn't provide a lot of information on the FW pump (other than never turn it on without water in the tank, and never use it with city water connected).
Also, I have noticed the while I really like the Kingsport 235BH that I have, the owner's manuals / documentation really suck. Is there a better source for information on the trailer systems / locations / and operation?