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RedandSilver

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Aug 25, 2016
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Does anyone know what the metal parts are for in the attached image?

When I use the flush feature on my coach to back flush the tanks, there are dips coming from these.
I have tightened the connections up - but every time I turn the water on to flush the tanks it dips from here.

Are the metal parts really needed?
If So why and what do they do?

 

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Those are backflow prevention valves, to stop the possibility of sewage being drawn back into the water pipes from the tanks you are flushing. You should probably replace them, but taking them out might leave a bad taste in your mouth! You can see the one way arrow on them, they work much the same as a diode would in an electrical system.

New ones need to be replaced in the same position as the old.
 
They actually stop the syphoning of the water from coming back at you when you disconnect the flusher.
Where exactly is the leak? Is it at the plastic pipe fitting or from the top of the backflow preventer?
 
Rene T said:
Where exactly is the leak? Is it at the plastic pipe fitting or from the top of the backflow preventer?
Click to expand...

There is the $64.000.00 question.  I'm alone and can't turn the water on and be inside to check where it's leaking at the same time.

Waiting for a neighbor to come home or another neighbor to call me back.  Until then I can't see where it's leaking from.

All I know is it's leaking down the hose(s) and drips inside the water compartment at a good rate.  The wood looked good so it
appears that it's indeed running down the hoses - but that can't be normal and I want it fixed while the weather is good.
 
the back one looks corroded to me....well actually both but all that black on the back one looks especially bad.

regardless, I'd replace them both if it were me, and try to find a non-metallic version...
here's one....and you can see what it looks like inside too!
even if you didn't go for this one at least this picture gives you a better understanding of what it is
https://www.amazon.com/Valterra-A10-3050-Check-Vacuum-Breaker/dp/B00KNBGSD4/ref=sr_1_47?ie=UTF8&qid=1501274688&sr=8-47&keywords=vacuum+breaker
 
Thanks for the link Brad.

Wow $50 for one!
Also it seems the plastic ones are the only check/vacuum valves , as the metal ones don't appear to have the check valve part.

I'm going to wait and see if the valves are really leaking or the hose connections are the problem.
Also don't know if it's only one part or both.  Yes I probably should replace both even if only one valve is leaking.
Hopefully it's a hose connection that's leaking and not a valve.
 
Similar valves are used in landscaping, and they are called "anti-siphoning" valves. I was always under the belief that you never mix metal and plastic fittings, but then, who am I, I am not a plumber.  If there is a leak, it is most likely coming from the rubber seal inside the round cap.  Some of those caps are screwed on, so you might be able to remove it and take a look at the seal.
 
Remove the clamps holding the pipes to the wall and separate the two assemblies to get a better look as to which one and where the leak is coming from. Looking at the picture, it almost looks like there are water droplets on the nut on the bottom side of the rear anti syphon valve.
 
We had one break once when the dealer winterized our camper (while it was in for other service) and forgot to blow out the tank flush line. It was like Niagara Falls under the camper.
 
cgmartin said:
Similar valves are used in landscaping, and they are called "anti-siphoning" valves. I was always under the belief that you never mix metal and plastic fittings, but then, who am I, I am not a plumber.  If there is a leak, it is most likely coming from the rubber seal inside the round cap.  Some of those caps are screwed on, so you might be able to remove it and take a look at the seal.
Click to expand...

And I very strongly suspect we have a winner... The rubber seals inside the valve.. Mineral build up on the seals or the effects of age have "Gummed" up the works.  Cleaning may be all it needs.
 
I have a similar one on the black tank flush system that leaked around the top cap (where the the screws are). I removed it, took it apart, cleaned it up and reassembled. Has been working just fine for the last 9 years. No new parts were required, just a thorough cleaning, as John said.

The technical documentation from the manufacturer of the valve for my particular unit called it a back flow preventer. Its purpose is to prevent contamination of the city's and trailer's potable water source from any black tank residue. (Although the flush system and potable (city) water entries are separate, both the trailer fresh water and the flush system inputs do come from the same park spigot.)
 
Well I thought I would UPDATE you all on what I did.

I decided to replace everything with new.  I also used metal check valves in place of the plastic ones.
Had a neighbor come over after it was installed and he turned on the water to back flush the tanks while I was
inside looking for leaks.  Found no leaks using either valve setup, so for now all is good.

I attached an image to show the new parts I put in.  I have to assume the old parts were original and lasted for almost 15 years.
So hopefully these will last that long or more.

Thanks to all that gave advice and helped me figure out what to do to fix the leaking that I believe was going on before I bought this unit.
But how many of you buy a used unit and back flush the waste tanks before you buy it?  I know I didn't.  And it took awhile to find where the leak was coming from too.
 

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Sounds like you fixed it.. I just found my water heater is leaking (Been leaking for about a month but I finally ID'ed the leak)  Good thing I have a service plan on this house, .
 
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