Reply
 
Thread Tools Display Modes
Old 10-19-2017, 11:42 PM   #1
Senior Member
 
Join Date: Feb 2016
Posts: 236
The infamous black tank vent valve

The first time we tried to use our black tank flush we stopped almost immediately because my DW was vigilant and spotted water coming out from under the bathroom wall. The camper was still under warrantee, and had a couple other issues, so we took it back to the stealership.

Next trip, no water flowed through the flush. Nada. Just pressurized the hose.

Thanks to the old interwebs (this forum and others) I came to an understanding of the function of the check valve / vent under the bathroom sink.

I checked it out after the second failure, and, sure enough, it's backwards. There is a clearly-marked flow direction arrow, and it is installed so the arrow is pointing TOWARD the hose connection. And, even though the top is clearly marked 'this side up,' the valve is not secured to anything, just hanging at the end of the hoses.

So, my assumption is that it was initially plumbed correctly, but not secured upright. Thus water leaked into the cabinet and ran under the wall. Then with the warrantee work the stealership reversed it. Thus the no-flow condition we have now.

I could just replumb it and secure it upright. But...

I don't like the idea of the vent being inside anyway. Why would I want stinky gas vented inside?

Besides, these plastic bits are less then reliable. Lots of threads about 'em breaking. Lots of people recommending replacing them with a residential version.

Then... At the hardware store I was looking at a simple hose bib vacuum breaker. Designed to screw onto a residential outdoor hose bib (aka faucet). It has a spring valve that serves as both vacuum release and check valve. When there is no inlet water pressure the valve seals the inlet and, at the same time, opens small ports to vent the backside to break the vacuum.

So, if I remove the factory valve and plumb the line straight from the tank to the existing hose connector, then add the hose bib vacuum breaker on the outside, it seems I would solve both my above issues. Get the vent outside, and remove a failure point inside. And be very simple to do.

It would not allow backflow into the city (campground) system because with the water on, well, there's water pressure to overcome. And with the water off the spring valve closes the inlet.

And at the same time those vacuum breaker ports would act as a vent the for tank.

The only thing I'm not sure of is how much pressure it takes to overcome the spring valve. It is possible that until enough pressure builds up it could spray water out the vent holes. But, hey, it's outside. And while not potable, it is 'clean' water. I can handle that if it's not too much water...

We're gong camping this weekend. I'll report back.
__________________

__________________
Family of six, camping in a Grey Wolf 26DBH LTD pushing a 2010 Armada via 10k/1k HaulMaster WDH stopped by a Prodigy P2 brake controller

Tug: 2010 2wd Nissan Armada Titanium with tow package.
Specs: Max Trailer Weight 9,100, Tongue Load: 910, GCWR: 15,100, GVWR: 7,150, Payload: 1,592
DadOfTwo is offline   Reply With Quote
Old 10-20-2017, 01:31 AM   #2
Senior Member
 
Scrapper's Avatar
 
Join Date: Aug 2013
Location: Central Wisconsin
Posts: 1,033
I Don't see why it wouldn't work. I believe all campgrounds are supposed to have that kind of vacuum breaker at every water connection. At least here in Wisconsin the state requires it.

The vacuum breaker only takes a few psi to open it. The spring is not too strong.
__________________

__________________
Richard & Jill
2014 Flagstaff 832IKBS - seasonal
2011 Silverado 1500 Ext Cab Z71 4x4
Scrapper is online now   Reply With Quote
Old 10-20-2017, 01:40 AM   #3
Senior Member
 
dbledan's Avatar
 
Join Date: Jan 2017
Location: KS
Posts: 465
I am no plumber but you will get a little wet when it vents but if you have it outside you should be fine.

I have one in my basement at home that I have had to attach a spray hose to in order to flush the flooded basement. I put a bucket around it and it only put maybe a half inch of water in the bucket using it with a spray nosel. It ran each time I stopped the water and let the pressure build.
__________________
dbledan is offline   Reply With Quote
Old 10-20-2017, 03:08 AM   #4
Senior Member
 
Witch Doctor's Avatar
 
Join Date: Feb 2012
Location: Clarksville Va.
Posts: 7,577
You can just use a backflow prevented, one way valve at the old location. Just keep the rise in the line above the tank and outside connector. You don't need a vacuum break, it's open at both ends.
__________________
Rockwood #8289 WS 2012
F250 6.0 / Husky 16k
With 4 point leveling system
Witch Doctor is offline   Reply With Quote
Old 10-20-2017, 07:05 AM   #5
Senior Member
 
Join Date: Aug 2016
Posts: 321
The backflow preventer does not vent vapors from the tank.

When water's off it is intended to block passage to the tank and allow air to come through the valve into the feed line so the garden hose can't suck stuff out of the tank.
__________________
johnbryanpeters is offline   Reply With Quote
Old 10-20-2017, 08:36 AM   #6
Senior Member
 
Witch Doctor's Avatar
 
Join Date: Feb 2012
Location: Clarksville Va.
Posts: 7,577
Quote:
Originally Posted by johnbryanpeters View Post
The backflow preventer does not vent vapors from the tank.

When water's off it is intended to block passage to the tank and allow air to come through the valve into the feed line so the garden hose can't suck stuff out of the tank.
I don't understand, that's why you have a vent pipe, a backflow preventer, blocks liquids from e tearing your flush hose.
__________________
Rockwood #8289 WS 2012
F250 6.0 / Husky 16k
With 4 point leveling system
Witch Doctor is offline   Reply With Quote
Old 10-20-2017, 09:13 AM   #7
Senior Member
 
bubbles's Avatar
 
Join Date: Dec 2012
Posts: 2,537
DadOfTwo
Then... At the hardware store I was looking at a simple hose bib vacuum breaker. Designed to screw onto a residential outdoor hose bib (aka faucet). It has a spring valve that serves as both vacuum release and check valve. When there is no inlet water pressure the valve seals the inlet and, at the same time, opens small ports to vent the backside to break the vacuum[/QUOTE]

This is exactly how the plastic valve works. That's why when installed backwards there is no flow through it. Also, the valve must be installed upright to function correctly. Of course, it is not as robust as the metal store version but the water pressures are not as high either. Actually, if you look at the plumbing routing associated with a factory installed RV black tank cleanout the valve is an (dare I say it) overkill.
__________________
bubbles is offline   Reply With Quote
Old 10-20-2017, 12:45 PM   #8
Senior Member
 
Scrapper's Avatar
 
Join Date: Aug 2013
Location: Central Wisconsin
Posts: 1,033
Vacuum breakers and backflow preventers are the same thing. The way they are designed prevents the flow of contaminated water back into the supply line. There are two different types.

One type has a ball or plunger which when there is water pressure against it the ball/plunger pushes up allowing water to flow. When the pressure is removed, the ball/plunger fall back down closing the input line. The water on the output side is drained into the tank. This is the type builders use in the black tank flush. This is also the type you see in the public men's restrooms on the top of urinals. Because gravity is the main way this type closes off the input it must be installed in the correct position with the water lines connected correctly.

The second type utilizes a neoprene flap that opens allowing the water to flow. When the water is turned off the back pressure causes the flap to be pushed back against the seat, allowing the excess pressure to be vented to the outside. This is the type you have at the campground water spigot. If you observe the spigot and have someone run some water in the rv, you will see the excess pressure being bled off when the water is turned off. This type can usually be installed in any position as long as you pay attention to the input/output connections on the hose bib type. Most are made so you can connect them to garden hose connections.

Both types can be effected by dirt, mineral deposits or trash in the water line causing the ball, plunger or flap to remain open.

You cane see both types by googling either vacuum breaker or backflow preventer.

Watts is a common manufacturer of both types. Vacuum Breakers, Backflow Prevention, Watts

Quote:
Originally Posted by johnbryanpeters
The backflow preventer does not vent vapors from the tank.

When water's off it is intended to block passage to the tank and allow air to come through the valve into the feed line so the garden hose can't suck stuff out of the tank.
If you do not have either the vacuum breaker or backflow preventer, or they are stuck open, and the liquids are above the end of the line, then you can get siphoning of the fluids back through the supply line. The vent pipe will not prevent this from happening.

The vent pipe is only there to let excess air out of the tank when the water/liquids go in. When you dump the tanks the vent pipe allows air back into the tank. Most campgrounds which have a honey wagon will not connect to your dump valves because the vacuum pump on the honey wagon will cause your tank to collapse if your vent pipe is blocked for any reason. Hornets can make a nest in the cap over your vent causing such blockage.
__________________
Richard & Jill
2014 Flagstaff 832IKBS - seasonal
2011 Silverado 1500 Ext Cab Z71 4x4
Scrapper is online now   Reply With Quote
Old 10-20-2017, 01:45 PM   #9
Senior Member
 
Join Date: Feb 2016
Posts: 236
Quote:
Originally Posted by Witch Doctor View Post
I don't understand, that's why you have a vent pipe, a backflow preventer, blocks liquids from e tearing your flush hose.
The under-cabinet vent is used in place of a vent pipe.
__________________
Family of six, camping in a Grey Wolf 26DBH LTD pushing a 2010 Armada via 10k/1k HaulMaster WDH stopped by a Prodigy P2 brake controller

Tug: 2010 2wd Nissan Armada Titanium with tow package.
Specs: Max Trailer Weight 9,100, Tongue Load: 910, GCWR: 15,100, GVWR: 7,150, Payload: 1,592
DadOfTwo is offline   Reply With Quote
Old 10-20-2017, 01:51 PM   #10
Senior Member
 
Join Date: Feb 2016
Posts: 236
Quote:
Originally Posted by Witch Doctor View Post
You can just use a backflow prevented, one way valve at the old location. Just keep the rise in the line above the tank and outside connector. You don't need a vacuum break, it's open at both ends.
Um, yes, I stated in my post that I could replumb or replace. And I also stated why I don't want to.
__________________

__________________
Family of six, camping in a Grey Wolf 26DBH LTD pushing a 2010 Armada via 10k/1k HaulMaster WDH stopped by a Prodigy P2 brake controller

Tug: 2010 2wd Nissan Armada Titanium with tow package.
Specs: Max Trailer Weight 9,100, Tongue Load: 910, GCWR: 15,100, GVWR: 7,150, Payload: 1,592
DadOfTwo is offline   Reply With Quote
Reply

Tags
black, black tank, tank, valve, vent

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



» Virginia Campgrounds

Reviews provided by




ForestRiverForums.com is not in any way associated with Forest River, Inc. or its associated RV manufacturing divisions.


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 12:17 PM.