Fresh Water Vent

[bilco82]

Dors anybody know if the fresh water tank has a vent other than the overflows?

[Cate&Rob]

The overflow is the only vent on a 150 Series Reflection 5th Wheel.

Rob

[bilco82]

The overflow is the only vent on a 150 Series Reflection 5th Wheel.

Rob

Cate&Rob, I'm trying to protect against the siphoning issue with my fresh water overflow. After some research on this forum, it appears I may have the "Rob Vent", (as referenced by TucsonJim) from the "Breaking Water Tank Overflow" .pdf you post in another thread. I have two blue pex tubes coming form my fresh water tank. If so, I don't need a shut off valve as I should not have any siphoning going on, correct?

[Cate&Rob]

Hi bilco82

The twin overflow pipes have proven to be successful at stopping the siphon action described in those other threads. What this will not stop is “slosh pumping”. If your drive to the campground involves a lot of stop-and-go driving with a full water tank, you will still lose some amount of water but if a siphon gets started, it will stop on its own.

Rob

[TedS]

The water will drain as long as the tank water level is above the tank vent port. The second tube allows the tank to gulp air to replace the draining water volume while water runs out the first vent tube. Siphoning is a misnomer for the draining water action.

[Country Campers]

The problem with the overflow pipes is in the installation. It will not matter if there are 1, 2, or 10 overflow pipes. If they are installed where they go up to be above the top of the tank before going down then they will work, if they are installed so they are below the top of the tank then they will siphon,drain, or whatever you want to call it.

Brian

[Cate&Rob]

This goes back to the original discussion of "siphon draining" of the tank. See the original thread, post 55 https://gdrvowners.com/forum/operati...ter-tank/page4 Once the siphon starts, a single vent/drain tube longer than the depth of the tank can create enough vacuum to lift the bottom of the tank such that the top connection point remains submerged. This is because the tank is so broad and shallow. Grand Design didn't believe this either . . . until they tested my theory and observed exactly this phenomenon. The second down tube breaks the siphon.

Rob

[TedS]

Just making U shaped plumbing doesn't make a siphon. Otherwise, simply not making the U shape plumbing at the vent would be enough to kill or prevent a 'siphon'.

[Cate&Rob]

Just making U shaped plumbing doesn't make a siphon. Otherwise, simply not making the U shape plumbing at the vent would be enough to kill or prevent a 'siphon'.

A column of water with its top end submerged in a reservoir of water makes the “siphon”. The shape of the tube does not matter. As described in the link to post 7, this column of water can create enough vacuum to lift the bottom of the tank, keeping the top of the drain pipe submerged. The second pipe allows air to be drawn into the column of water which breaks the vacuum.

Rob

[TedS]

The inhaled air breaks the water column. The long leg empties and the water/air in the port flows back into the tank allowing the tank to go to atmospheric pressure, regain its shape and drop the water level below the port to stop draining.

Regardless, your construct works.