Water pressure - why does pump run when city water connected

[Dan_Diego]

I mostly dry dock and have only recently began to camp where water and electrical hook-ups are available. When connected to city water, I have a 40psi regulator in between the city hose bib and the trailer's city water connection. I have not mapped my water system but have looked at general rv water distribution diagrams. It appears that fresh water tank is on inlet side of the pump while the city water connection joins the water system on the outlet side of the water pump. I do not understand why the water pump runs when under city water pressure. I would guess the pump runs as a result of the loss of pressure on the outlet side when a faucet runs (loss of the 40psi). Is the running pump then trying pump what ever remains in the fresh water tank until it is empty...and if so, is it damaging for the pump to run once the fresh water tank is completely empty?

[Dan_Diego]

Thanks for all of the feedback. And as mentioned, camping with hookups still has me feeling a bit like a fish out of water. We are going to be camping with the hookups again in a month. I will see how we do with out the pump running.

[nayther]

we often turn on the pump when taking showers if the campground pressure is too low.

[arhayes]

dedmiston wrote:
Hey Dan - Dumb questions are OK here. Welcome to the forum.

For starters, the other comments are right that you should definitely turn off the pump when you're connected to city water. It's an either/or thing.

There's something interesting about what you said though. You mentioned that you have a 40 PSI regulator and the pump is also running. I don't know this for certain, but I would take that to mean that your pump puts out more than 40 PSI and is making up the difference between its max and the 40 PSI coming from the city inlet.

(That could be totally off, but it's an interesting puzzler.)

You also bring up another peculiarity of the toy hauler community related to full hookups. Most of the toy hauler owner's I see here and on other forums are primarily boondockers and we feel like bumpkins when we go to an RV park and don't know how everything works. My wife and I took a 10,000+ mile trip last fall and I still felt like an imposter at the end, even after setting up at RV parks for months.

I'm used to seeing my buddies unpack all their gear and level up their rigs by digging holes in the dirt. On the rare trips when we have hookups, it's funny to watch everyone staring down the end of their water hoses and tangling up in their shore power cords like circus bears. It's such a different culture.

To your point, my pump has a stated pressure setting of 45psi, so a reducer to 40 would guarantee it would try to maintain that level When powered on. I also wonder why the OP would want to throttle down to 40Psi. I have used a 55psi regulator since we began full-timing in our rig. There have been a few parks in our 6 years of travel that didn’t provide that much pressure so then we WOULD operate from the tank using the pump. As always, YMMV.

[schlep1967]

If your regulator is adjustable, turn it up to 50 PSI and see if it still happens. My guess is you have a pump that provides close to 60 psi and has a low end pressure above 40 PSI. So it kicks on to make up the pressure difference.

[Dirtclods]

dedmiston Very well stated!

[dedmiston]

Hey Dan - Dumb questions are OK here. Welcome to the forum.

For starters, the other comments are right that you should definitely turn off the pump when you're connected to city water. It's an either/or thing.

There's something interesting about what you said though. You mentioned that you have a 40 PSI regulator and the pump is also running. I don't know this for certain, but I would take that to mean that your pump puts out more than 40 PSI and is making up the difference between its max and the 40 PSI coming from the city inlet.

(That could be totally off, but it's an interesting puzzler.)

You also bring up another peculiarity of the toy hauler community related to full hookups. Most of the toy hauler owner's I see here and on other forums are primarily boondockers and we feel like bumpkins when we go to an RV park and don't know how everything works. My wife and I took a 10,000+ mile trip last fall and I still felt like an imposter at the end, even after setting up at RV parks for months.

I'm used to seeing my buddies unpack all their gear and level up their rigs by digging holes in the dirt. On the rare trips when we have hookups, it's funny to watch everyone staring down the end of their water hoses and tangling up in their shore power cords like circus bears. It's such a different culture.

[opnspaces]

Definitely turn the pump off when not in use. No it will not damage the pump to run dry so I wouldn't worry too much there. there is a pressure switch on the pump that turns it on and off as water pressure rises ad falls. Either that switch is bad, or the city water pressure is too low.

[Dan_Diego]

Thanks for the reply. Feeling particularly humble at the moment.

[Ivylog]

Just turn the pump off unless you need the extra pressure and yes, you’ll eventually empty the tank.