Why does my water work when the pump is off?

[TMG51]

Maybe there's a simple RV systems answer to this that I'm just not aware of, but my understanding of how the on-board water tank worked was that the pump would have to be on any time you want any water. That only makes sense because there is no city water pressure to drive it.

So why is it that when my water pump is off, water still comes out of my faucet? Both hot and cold run. I've even taken a shower before noticing I forgot to turn the pump on. (I don't stand under the water constantly, I wet myself in spurts to conserve water.) Does the pump pressurize the system? Except that can't be, because the fill and air hoses aren't sealed off....

I'm sure if I ran the water for a minute it would stop but I haven't wanted to waste the water to test how long it'll go. I'm perplexed that it could run even a drip with the pump off. Water should just fall back down the lines with no pressure and no pump going. The hot water makes a little more sense because it probably is pressurized in its tank as it gets heated by the propane. But that doesn't explain the cold water which comes from the vented holding tank.

 

[coolmom42]

Maybe there's a simple RV systems answer to this that I'm just not aware of, but my understanding of how the on-board water tank worked was that the pump would have to be on any time you want any water. That only makes sense because there is no city water pressure to drive it.

So why is it that when my water pump is off, water still comes out of my faucet? Both hot and cold run. I've even taken a shower before noticing I forgot to turn the pump on. (I don't stand under the water constantly, I wet myself in spurts to conserve water.) Does the pump pressurize the system? Except that can't be, because the fill and air hoses aren't sealed off....

I'm sure if I ran the water for a minute it would stop but I haven't wanted to waste the water to test how long it'll go. I'm perplexed that it could run even a drip with the pump off. Water should just fall back down the lines with no pressure and no pump going.

In any RV there is some residual pressure left in the lines.  The pump has a check valve to keep the water from running backwards through it.  So it just can't "fall back" down the lines.

You may also have a small pressure tank, similar to the large version used with residential well pumps.  This is designed to keep the pump from constantly going off and on.  If you have one, the tank can hold 1-2 gallons of water.

 

[TMG51]

Hm, so there must be check valves and it's just a matter of residual pressure between the valves and the fixtures. That must be the only answer. I'm surprised it's as much as it is. I don't think I have a pressure tank but it's possible they may have hidden one somewhere. This thing continues to surprise me.

 

[Almost There]

Hm, so there must be check valves and it's just a matter of residual pressure between the valves and the fixtures. That must be the only answer. I'm surprised it's as much as it is. I don't think I have a pressure tank but it's possible they may have hidden one somewhere. This thing continues to surprise me.

At least it's good surprises...

The check valve is built in to the pump and there's usually another one at the fill inlet where you hook up city water.

A good test to see if you do have a pressure tank would be to leave a tap running while the pump is off so that you can find out how much water comes out before you run out. Do it with the cold water tap only or you'll be draining the hot water tank.

 

[SoulRaven]

You probably have an accumulator tank in your system which stores both water and pressure to both equalize the water pressure and also lower the strain on the water pump. Some systems actually put out much higher pressure than the pump actually provides by using this method.

I have seen accumulator tanks as big as 5 gallons in some pretty small rigs.

 

[highdesertranger]

x2 on the accumulator tank. it sounds like you have a rather large one at that. without an accumulator tank you would get one good spurt of water and that's it, maybe 1-2 seconds worth. highdesertranger

 

[ZoNiE]

I have an accumulator. Does just that. I used an RO system tank. I wouldn't say I could take a shower, but the reason I installed it was to be able to flush at night without turning on the pump with the very bright light right across from the bed!

 

[ZoNiE]

I have an accumulator. Does just that. I used an RO system tank. I wouldn't say I could take a shower, but the reason I installed it was to be able to flush at night without turning on the pump with the very bright light right across from the bed!

Look for one of these:

or this: