Water tank vent line valve

[timfuji]

On my 192hw near the fresh water tank drain valve there is another hose that goes to a vent next to the fresh water fill hole. There is a valve at the end of the vent hose just before it connects to the tank. What is this for?

[RSchleder]

To vent air from the tank, keep everything else out.

[timfuji]

Thanks for the reply. So do I keep the valve closed? I assume that I'd I have water in the tank and I open it water will drain out. So closed water won't drain but air can vent?

[rockfordroo]

A valve in the vent line that goes to a vent by the FW fill seems unusual.

Many larger TT's have vents that are simply an inverted U that come out of the bottom of the TT, rather than going back up to the FW fill connection. These units may have a valve (or the owner installs a valve) to prevent siphoning of water out of the tank while you're driving down the road. (See vent in attached pic, although it doesn't show a valve). Since the vent normally doesn't really come out of the top of the tank, but somewhere on the side, when you make a turn, the water sloshes into the vent. If it gets to the top of the U, it creates a siphon and will drain the tank down until the level is below the level of the vent connection. Some people report they've lost half a tank of water due to this. Putting a valve in the vent line prevents this siphoning effect.

In your case, since the vent goes up to the FW fill, and therefore shouldn't have an inverted U, it doesn't make sense to have one. I'd leave it open.

[5picker]

Is it a valve that can be turned or an inline check valve?
A picture would be helpful.

[timfuji]

Yes you can turn the valve. I'll take pictures when I get home.

[Butch Wilson]

My t21QBHW has this same drain valve on the vent line. I assumed it was to drain any residual water in the vent line when winterizing. I keep it closed.

[timfuji]

OK it looks like I was wrong. Before this I had only stuck my arm under the camper enough to open or close the drain on the tank, but to get a good picture of the valve I crawled under the camper. Even then I didn't notice until after looking at the picture that there were 2 hoses there. The hose further back in the pic is the one going up to the vent hole. The hose in the foreground with the valve is the hose going to the water pump and the valve must be to connect a hose and stick it into a bottle of antifreeze! I bought a kit to put on the pump to suck antifreeze and was going to install it this fall. Guess I won't be needing it after all...