Switching between city water and holding tank

[dh]

I'm putting in a city water connection as well as a holding tank/pump. I know my set up is not normal, as I have no hot water, I'm going to plum the city water connection straight to the "hot" water valve on the sink, and the pump to the "cold" valve, and put in a switch to kill power to the demand pump when it is not needed. How do they valve this in the big rigs? Also, with my set up, do I need check valves to keep water from flowing where it shouldn't if somebody opens both valve handles at the same time?

[Shadow Catcher]

If there is no connection between the two circuits other than at the faucet you don't really need a check valve. The only instance where this might not be true would be if both valves were open simultaneously and the restrictor caused the higher pressure to try and back feed, but then check valves are inexpensive and pumps are not. Ours because it has a water heater has a check valve to keep water from entering the fresh water tank which has a filler that is open to atmosphere. The check valve and Y connection are just after the pump.

[48Rob]

A check valve would normally be installed in the cold water line in front of the 12 volt pump, to keep city water from trying to go backwards through the pump into the holding tank.

I would do the same in your setup, just in case, as if both faucets are opened at the same time while connected to city water with higher than average pressure, it will put undue strain on the pump.

It might be simpler, and cause less confusion to simply install two separate faucets.
They will each fit perfectly in a standard sink with holes at 8" centers.
Rob
<img src="http://ecx.images-amazon.com/images/I/31KKSEKF2FL._SL500_AA300_.jpg">

[bobhenry]

Now two totally seperate delivery systems you need some lables.......




Country water City water

so I found you some labels !

[Larwyn]

RV water pumps usually have a built in check valve on the pressure side to prevent back flow into the fresh water tank. When you see a large puddle under an RV it is often due to failure of this check valve which allows city water to over flow the tank. There is also a check valve built in to the city water connection which prevents water escaping at that point when using the on board water system.

On my 5th wheel, I installed a ball valve to bypass the pump so I cold fill the fresh water tank from the city water connection. I just had to remember to close the valve once the tank was filled. This saved a lot of hassle since the city water connection was on the back of the trailer and the fresh water fill was located on the front.

[Dale M.]

Why do you think its necessary to have two systems.... Keep it simple.... Just use city water to fill tank and use pump to supply faucet...

Dale

[dh]

Why do you think its necessary to have two systems.... Keep it simple.... Just use city water to fill tank and use pump to supply faucet...

Dale

Necessary, no. What I want, yes.

If sticking to necessary, I wouldn't have a sink or a holding tank, just a bucket. In fact, I wouldn't even be camping at all, as it really isn't necessary now is it?

[dh]

RV water pumps usually have a built in check valve on the pressure side to prevent back flow into the fresh water tank. When you see a large puddle under an RV it is often due to failure of this check valve which allows city water to over flow the tank. There is also a check valve built in to the city water connection which prevents water escaping at that point when using the on board water system.

On my 5th wheel, I installed a ball valve to bypass the pump so I cold fill the fresh water tank from the city water connection. I just had to remember to close the valve once the tank was filled. This saved a lot of hassle since the city water connection was on the back of the trailer and the fresh water fill was located on the front.

Larwyn, could you post a diagram, I like the idea of filling from the city water connection.

[Larwyn]

RV water pumps usually have a built in check valve on the pressure side to prevent back flow into the fresh water tank. When you see a large puddle under an RV it is often due to failure of this check valve which allows city water to over flow the tank. There is also a check valve built in to the city water connection which prevents water escaping at that point when using the on board water system.

On my 5th wheel, I installed a ball valve to bypass the pump so I cold fill the fresh water tank from the city water connection. I just had to remember to close the valve once the tank was filled. This saved a lot of hassle since the city water connection was on the back of the trailer and the fresh water fill was located on the front.

Larwyn, could you post a diagram, I like the idea of filling from the city water connection.

It's really simple. Just tap the water line on the pressure side of the pump/check valve with a pipe T, repeat on the low pressure/tank side with another pipe T, then install a valve between the two T's, with a bit of pipe. It simply bypasses the pump and thus the internal check valve. If you use an external check valve then you will need to be sure that you include it when you bypass the pump. If you open the valve when connected to the city water supply the tank will fill through what is normally the tank's outlet to the pump. This valve should only be open when you wish to fill the tank.

Sorry, I an not able to draw a diagram, I have never been able to get AutoCad LT 97 to work with Windows Vista and that is all I have to work with here.

[48Rob]

DH,

If you go with filling the tank with the city water bypass, be sure you use a water tank fill door/setup that has the tank vent terminating at/near that point.
If you choose to eliminate the gravity fill, be sure the holding tank air vent is a couple feet higher than the tank, and terminates on the exterior of the trailer.
When the pressurized water has filled the tank, it will then proceed up and out the air vent if you don't turn it off in time...

Rob

[bobhenry]

If I am understanding correctly.......

[rbeemer]

Do you have to turn on a switch to activate your pump for water. If so you could just simply put in two valves(one from the pump side and one from the city side. So then all you would have to do is open and close the correct valve depending on if you are using city or your holding tank.

This would keep the need for one faucet and in the future you could put in a hot water setup with out much re-piping.

Just my thoughts

[Larwyn]

If I am understanding correctly.......

That's purty much it only the two faucets are combined to one supply to all cold water faucets and the input side of the water heater in the version that I did on the 5'er.........

[dh]

Thanks for the replies. Larwyn, great idea, I promise I'm going to steal it. The pump is a demand pump, but I'm putting in a switch as a safety feature, so if something goes wrong, like a faucet valve develops a leak, I won't arrive at my destination with an empty holding tank and a full grey water tank