Another tank flushing question?

[sandy43]

After reading about a few folks with water problems because of the vacuum breaker valve in the tanks flushing system, I talked to a person last night who has a rather new Montana (I assume Alpine has the same set-up) and he had the same problem about water in the bathroom area. His dealer told him if he closes the black tank valve when the flushing system is on and operating somethings got to give and usually it's the fittings, mainly the one that's connected to the vacuum breaker valve. He admitted, rather his wife did, that he closed the valve on the black tank thinking it would clean it better. Could this be why several people had a water problem? I'm trying to learn this system the best I can. Sorry for the long rant. Thanks

[laidback]

I close mine for 2 or 3 min then open it back up and have never had a problem. I don't think I would leave it closed until the tank got full. If it got to full it would have to go somewhere, but being only a few gal it should be at the bottom of the tank.

[golfpro]

I shut the valve when using mine. I installed it half way up the wall and I listen to when the water noise changes and then open the valve and let the water out and all the black it washes off the walls. If you let it stay closed then you are asking for trouble.

[hankaye]

sandy43, Howdy;

I got rid of the cheap POS valve that came with the trailer. It came apart when I used it the first time. I replaced it with a simple elbow.

I do close the valve when flushing out the black tank. I don't even consider any form of multi-tasking when it's dump time. I'll keep the valve closed for 3 minutes then pull the 'T'-handle repete. Then I disconnect the flush hose. close the tank valve. I'll go inside and fill the tank with the foot valve. Then go outside and pull the 'T'-handle one last time. Back inside I drop 2 scoops of oxy-clean and 2 caps of downey to the empty tank and fill the bowel 3 times so any new 'deposits' have something to swim in...

hankaye

[webslave]

Closing your black tank valve shouldn't have any effect; don't know why a dealer would say otherwise, unless he has no idea how a vacuum breaker works. I've always used the black tank valve to "add water" to increase flow when emptying the black tank with no ill effects.

Picture an inverted "V" (/\) with the vacuum breaker at the top. It basically is a pressure operated valve. As long as there is water pressure on the valve, the valve closes off the vent and passes water through the "V" and into the tank. Even with the tank full, the pressure should keep the valve closed. When pressure is totally removed, i.e., the ends of the flush line are open to atmosphere, the valve will open (no pressure holding it closed) allowing water to flow back down both sides of the "/\", but, due to gravity, not up and over the "/\". That's why it is a "vacuum breaker"...breaks the vacuum caused by the downhill flow of water from its highest point (that's why they are located so high, usually under the bathroom sink, uphill from both the water inlet and the flusher).

Several things can cause those valves to leak...age (the seals deteriorate), broken components (age or just, most likely, a cheaply built unit), or contaminates in the water that prevent a good seal and over pressurization. Most of us, at sometime or another will have to deal with the usually cheap component aspect and replace the unit with a better made unit. I, personally, haven't ever had an issue with any of them on my trailers and the only thought I have on that is that I use the same filtered water as I drink...I have a whole house filter that removes sediment and chemicals and I use that same filtered water in my flushers; I also limit the water pressure to 40 psi. I have a Watts regulator that takes the CG water pressure down to 60 psi and I use a second pressure regulator on my flusher hose to further reduce it to 40 psi for use with the flushers... Or it could be that I'm just incredibly lucky

[SmittysRV]

Okay good to hear you can run the santi flush with the valve is closed...... it says right on mine to make sure the valves are always open when using the santi flush. I thought that using the santi flush with the valve closed will just fill the black tank and assist with the flow when emptying. I also use the pressure regulator when using the santi flush, just never knew if I needed to. Thx

[webslave]

Most manufacturers and accessory manufacturers (those that manufacture add-on tank flushers) will tell you not to use them with the waste gates closed...my guess would be a liability avoidance should you forget and let the flusher run until the tank gets "over filled". Nasty things can happen when water is forced into a virtually closed environment (the rules of hydraulics apply...the vent stack will take some, but, you wouldn't believe the pressure developed in the tank as that happens; the vent is designed to vent "fumes" not liquid). I've heard tales of ruptured tanks, broken toilets, etc.

As long as you only leave it closed for a minute or so, if you start with the tank almost empty, you aren't doing anything more than "a long flush" with the toilet by adding water in that fashion. Just be mindful of the time

[albertr]

My vacuum breaker fell apart. Dollar Store quality item.

[allentx1]

I also close my valve when flushing. About 3-4 minutes is all I can tolerate without worrying. I have yet to have an issue with the leakage as mentioned, maybe it's just the luck of the draw.

[Quiroule]

OK, I am new to this.

Where is the vacuum valve located and does it do for me.

[SteveC7010]

Originally Posted by Quiroule

OK, I am new to this.

Where is the vacuum valve located and does it do for me.

There are already several extensive threads on the vacuum breaker, its probable location, and its function. Search on vacuum breaker to find them.

In short, if you have the factory installed black tank sprayer/flush system, the water line goes from the connection up, usually into the bathroom under the sink to a vacuum breaker and then down to the flush/sprayer inside the black water holding tank.

The purpose of the vacuum breaker is to prevent a siphoning action which could back feed black water into the fresh water hose connected to the flush system. The vacuum breaker needs to be several feet above the black water tank and the shore line connection to work properly.

[geo]

Steve is quite correct - several times we have fallen into the vacuum of the black tank vacuum breaker. Here's one of those threads with a diagram:

http://www.keystonerv.org/forums/sho...ghlight=vacuum

If you looks in Mods, you will find a post from Geo describing how and why I replaced my vacuum breaker with a 200# WOG anti-back flush valve.

Ron

[Patrick Ely]

Another problem with my Montana! I was flushing the black tank and found water leaking out in the pocket door and bathroom area. I found that the vacuum break was leaking. The great part of this is that it is located where there is no access! I had to cut a hole in the pantry paneling to get to it. Wonderful engineering! That is the second hole I had to cut since the pocket door also fell from the ceiling after a short trip. There is no way to access this without removing the shower! And all of this with less than 3000 miles of towing!

[chuckster57]

Originally Posted by Patrick Ely

Another problem with my Montana! I was flushing the black tank and found water leaking out in the pocket door and bathroom area. I found that the vacuum break was leaking. The great part of this is that it is located where there is no access! I had to cut a hole in the pantry paneling to get to it. Wonderful engineering! That is the second hole I had to cut since the pocket door also fell from the ceiling after a short trip. There is no way to access this without removing the shower! And all of this with less than 3000 miles of towing!

Often times, and it may not be in your case, if the vacuum breaker is behind the shower all you have to remove is the faucet assembly.

[Scalemaster]

Mine was located in the wall behind a small panel above the toilet. I cut it completely out and direct connected it from the connection point to the black tank. I added an anti siphon valve to the hose connection point. I can't imagine the damage this would have caused if it filled the interior of the wall with water.

[Jimbeau]

You need to be VERY CAUTIOUS when adding water to the black tank with the valve closed. This guy we camped with accidentally put the fresh water hose onto the black tank flusher, walked away, then saw "water" leaking profusely from the bottom of the 5th wheel. The pressure had built up and it blew out his black tank (for a nice $850 repair!!). After seeing that I had my wife color the flushers cap with red nail polish and no more confusion when your trying to rush to get hooked up.
When mine was (luckily) still under warranty the vaccum breaker check valve on mine actually blew out and started leaking water all over outside. My RV guy said it was happening on a lot of trailers, and replaced it with a plain elbow bend. The only difference is you need two hoses, one dedicated "dirty water" for flushing and another for "fresh water".

[dcg9381]

So I don't entirely understand the function of the valve. I always thought that these were designed like homes, basically that plumbing was "vented" to the roof. Why is a check valve necessary for air flow?


Clearly the recommendation is not to flush with the valves closed, but I've been doing that for years - perhaps now I know why I shouldn't?

I assume if you want to get a good flush of that tank, you need to feed water in from the top to fill it from the top via non-pressurized means?

I learn something on this forum every day...

[SteveC7010]

Originally Posted by dcg9381

So I don't entirely understand the function of the valve. I always thought that these were designed like homes, basically that plumbing was "vented" to the roof. Why is a check valve necessary for air flow?

Clearly the recommendation is not to flush with the valves closed, but I've been doing that for years - perhaps now I know why I shouldn't?

I assume if you want to get a good flush of that tank, you need to feed water in from the top to fill it from the top via non-pressurized means?

I learn something on this forum every day...

It's not blocking air flow, it's blocking the flow of liquid. The vacuum breaker on the black flush line prevents any possibility of a back flow of contaminated water into your hose and possibly into the plumbing of where ever you are getting your water. It is an anti-siphon device.

If you remove the vacuum breaker, it's essential that you use an anti-siphon bib on your hose that you connect to the black tank flush. IMHO, it should be placed on the end of the hose connecting to the trailer's fitting.

[Quiroule]

I too thought that the black water tank was vented to the roof. If not, where is-it vented?

[SteveC7010]

Originally Posted by Quiroule

I too thought that the black water tank was vented to the roof. If not, where is-it vented?

It is vented to the roof. The black tank flush system has nothing to do with the venting of the black tank. As I just said in my previous post, the vacuum breaker in the black tank flush plumbing is an anti-siphon device.