failed vacuum breaker

[mvintx]

Can someone explain to me how the failure of the vacuum breaker installed in my RVs lavatory sink basin can allow water from the sewage rinse to leak into the RV? I don't understand how the system is plumbed. I made the bad assumption that water applied to the sewage rinse port goes only to the nozzles in the black tank.

Another item added to my growing collection of spare parts to be carried.

[MFL]

That is designed as a backflow preventer, and are known to leak, especially under low water pressure condition. Yes, it is a direct line to the black tank spray nozzle. It is not truly needed, and can be omitted until replacement is found. It is best choice to have one in place, due to possible, but unlikely backflow contamination.

[mvintx]

Fortunately I was home and flushing the tanks after a short trip.

I've got two of them on order, but why is the sewage rinse plumbed that way? I see several posts about these things failing but don't understand the logic behind it.

These RVs are a never-ending learning experience.

[LTurley]

They seem to always leak, sometimes a lot, and they also seem to really restrict the water flow. I cant think of any negative effect from removing it except maybe in a hard turn with a full tank...

[Stircrazy1]

Originally Posted by mvintx

Can someone explain to me how the failure of the vacuum breaker installed in my RVs lavatory sink basin can allow water from the sewage rinse to leak into the RV? I don't understand how the system is plumbed. I made the bad assumption that water applied to the sewage rinse port goes only to the nozzles in the black tank.

Another item added to my growing collection of spare parts to be carried.

how full did you fill your black tank for that to happen? if you didn't overfill the black tank with the rinse I would be stumped on that one also, I know they are in the same line but there should be no pressure as your black tank vent should take care of that.

[mvintx]

Originally Posted by Stircrazy1

how full did you fill your black tank for that to happen? if you didn't overfill the black tank with the rinse I would be stumped on that one also, I know they are in the same line but there should be no pressure as your black tank vent should take care of that.

The black tank was empty. The dump valve was open. I could hear water running when I started adding fresh water through the sewage rinse port but there was no rinse water coming from the black tank.

Makes no sense to me. Why would sewage rinse water go anywhere but directly to the rinse nozzles in the tank????

[Jkwilson1989]

Originally Posted by mvintx

Fortunately I was home and flushing the tanks after a short trip.

I've got two of them on order, but why is the sewage rinse plumbed that way? I see several posts about these things failing but don't understand the logic behind it.

These RVs are a never-ending learning experience.

Because if a hose is hooked to the rinse port and water pressure is lost the black tank contents could siphon back into the water supply without a properly installed vacuum breaker.

[mvintx]

Originally Posted by Jkwilson1989

Because if a hose is hooked to the rinse port and water pressure is lost the black tank contents could siphon back into the water supply without a properly installed vacuum breaker.

That makes sense but what does not make sense is why sewage rinse water would go anywhere but the sewage tank?

[MFL]

The black tank rinse line, with backflow preventer is purpose designed to be 6"s higher than other water feed lines in trailer, even though they are not connected.

I am sure the RV manufacturers don't care about potential CG water system contamination, but have to comply with regulations. Most CG water spigots have some sort of backflow preventer attached to faucet. Many of those leak too, while in operation, and drip on the ground around spigot.

[Old-Biscuit]

RV Black Tank Flush System




Anti-siphon Vacuum Breaker is usually inside the bathroom sink cabinet



water goes in bottom pushing disc up closing off air slots in top then out the side and down to the tank nozzle
water turned off, disc drops allowing air in tank side and breaking any siphoning effect

[mvintx]

Thank you for the pics. Looks just like my setup. I guess it's plumbed that way to prevent sewage water from flowing back to the rinse port. Now that makes sense. My thanks to all who replied.

[Stircrazy1]

Originally Posted by Old-Biscuit

RV Black Tank Flush System




Anti-siphon Vacuum Breaker is usually inside the bathroom sink cabinet



water goes in bottom pushing disc up closing off air slots in top then out the side and down to the tank nozzle
water turned off, disc drops allowing air in tank side and breaking any siphoning effect

you know, I have never seen where mine is in my 5th wheel, now I am going to have to go find it

[MFL]

Originally Posted by Stircrazy1

you know, I have never seen where mine is in my 5th wheel, now I am going to have to go find it

Under the sink, a piece of cake, to check for leaks, or changeout. Mine; behind shower hot/cold valves, that need to be loosened, pulled out, to just see the vacuum breaker. I've not needed to change it, but what a pita that would be.

If mine leaked, who knows where the water would go, or if you'd even know it was leaking, until damage has occurred. I used mine a few times, after purchasing my FW new. After learning of the leaks, knowing where mine is located, I no longer use it.

IMO, this system is just another sales gimmick, and not a good tank flush. I have to think dumping a bucket of water down the stool would give equal/better results. After dumping I add 2-3 gallons of water to black tank, to splash around while driving, which keeps my gauge fairly accurate, and liquifies any remnants in the tank.

[Lowflyer1]

In my coach there is just a simple check-valve at the water inlet, no vacuum breaker.
Think of that vacuum breaker to the new gas can filler tube regulations when the EPA got involved and started mandating those. What a PITA. I have replaced all those to the old style straight tube.