Black Tank Flush Vacuum Valve Replacement

[geo]

I had not had any problems with the vacuum breaker valve on the black tank flush system, but just knowing where the lines to this valve ran made me nervous. (VacBrk_before.jpg) In the picture VacBrk_before.jpg, one can see two Pex lines to the left of the Iota Transfer Switch that press on the switch case and disappear above the case. Those Pex lines run up into the wall between the toilet closet and the bedroom to the vacuum breaker valve. There is no access to this valve from either the toilet closet or the bedroom. I viewed this as just a bad accident waiting to happen.

When I replaced the Iota Transfer Switch, I also replaced the vacuum breaker valve. I found a brass check valve rated to 200 pounds pressure WOG (water-oil-gas) with half-inch thread. There were already two half inch connections on the black tank flush Pex tubing behind the WaterWorks area. It was a very simple matter that took no time at all to unscrew the existing fittings, move the old Pex to the side, and install the brass check valve in place. (Check_valve.jpg)

To finish the installation, I used a cable tie to secure the check valve to the aluminum structural member in an upright position. The flapper gate inside the check valve is gravity influenced to remain closed when no pressure is applied, thus there is an "up and down". The "blocked portion of the Y" should be above, or upright, of the flow connections.

As there was no way to remove the vacuum check valve (it was secured in the wall space), I pulled the Pex piping down as far as I could, cut and removed it. I used a low-expansion foam to seal the two inch hole that remained.

Ron

[DocData757]

if I am understanding you correctly, you replaced a Vacuum breaker valve with a sealed check valve. If that check valve develops the slights leak on its seat, you could be siphoning waste back into the fresh water system of your campground.

Granted your system, so long as the check valve seat remains perfect and the campground fresh water system remains pressurized, will probably prevent this.

Maybe I am misunderstanding you. I hope so because, to the best of my knowledge, a check valve is not a suitable replacement for a vacuum breaker valve.

[geo]

Originally Posted by DocData757

if I am understanding you correctly, you replaced a Vacuum breaker valve with a sealed check valve. If that check valve develops the slights leak on its seat, you could be siphoning waste back into the fresh water system of your campground.

Granted your system, so long as the check valve seat remains perfect and the campground fresh water system remains pressurized, will probably prevent this.

Maybe I am misunderstanding you. I hope so because, to the best of my knowledge, a check valve is not a suitable replacement for a vacuum breaker valve.

DocData757 -

Yes, you have interpreted this properly. And you are correct, the check valve is not a single mode of protection to prevent siphoning. However, with a back flow preventer valve (from HD) attached to the hose outside, combined with the check valve does offer better protection for the supply side and the inside!

For one, I have never left my black tank flush line connected to the water supply line for any longer than I have used it. Actually, I can't imagine why I would want to leave the water running through the black water tank sprayer for any longer than flushing my black water tank and adding a couple of gallons for the "new load". I also only attach the hose to the black water tank spray system when I need to dump the tank.

And secondly, on both my input white fresh water hose and my green black water tank sprayer hose, I have separate permanently attached back-flow preventer valves from HD. With the handy set screw on the back-flow preventer valve, it just doesn't come off the hose without a wrench! Plus, to siphon anything, a continuous, unbroken line of fluid must stretch from the source to a higher point, and then descend to a lower point than the source. That means the check valve would have to develop a leak plus the black tank would have to develop enough pressure to over come the 40-50 pounds pressure applied with the faucet is turned on. Add that back flow preventer . . . just isn't going to happen. And if it did, I would probably have a black water volcano from the top vent of the Alpine!

I would like to add, I believe this brass check valve is probably more reliable than the plastic vacuum breaker valve formerly located above the 240VAC 50amp automatic transfer switch case. I would argue that the use of two different types of valves to prevent backflow and prevent siphoning of a full black tank (as the spray head is located only 2" below the top of the black tank - I measured it!), and both these valves made out of brass . . . that certainly seems to trump one unseen and unreachable plastic valve located in a wall above the whole electrical input for the RV. And from recent and past posts on just this Forum alone, I would guess brass valves might have a higher degree of reliablility than plastic.

Ron

[DocData757]

Sounds good to me!