Pressure tested my black tank

[Garypowell]

We were leaving Raleigh, NC yesterday and as usual I cleaned out the black tank. After the initial dump I had the tank wash on with the gate valve closed. I am sure many of you do this after the initial drain. I put a fair amount of water in the tank and then get another good “whoosh” when I open the valve. Then close the valve and let it run for another minute to get some water in the tank and then close down the operation.

Well for the 3[SUP]rd[/SUP] time in 17 years I forgot what I was doing….and let the tank fill all the way up. I was over yacking to another RV’r and simply forgot. We found out my mistake (probably after the tank was full for 10 minutes or more) when Linda flushed the toilet and there was an eruption.

I realize by now many of you are getting this horrible image in your heads. Fortunately, it was not that bad (of course don’t ask Linda). She let the peddle go quickly and the “seal” held again. Obviously she came looking for me.

When I heard her voice I knew exactly what had happened and rushed over to the Rig and shut off the flush water inlet. Wow….did I get a whoosh when I opened the gate valve. The tank has probably not been cleaner since we purchased it!

I write this for two reasons:

1. Confession is always good for the soul and I think writing this story will not only help me….but it just might help someone else too.
2. I have a question from this experience…..why did the water not blow out of the vent and on to the roof? I had the pressure regulator at 55 PSI so there was a fair amount of pressure inside the tank for 10 minutes or so.
My only guess is that the column of water was “heavy” enough to counterbalance the force from the inside of the tank. But again 55 pounds……

So I am curious if anyone with the right kind of experience has a though on why nothing blew out the top.

I did a thorough inspection and the tank was still intact. No rupture or leak. Oh, and it only took two towels to mop up the “water” on the bathroom floor….and nothing got on Linda!

 

[Bobby A]

I think this has happened to a fair amount of us, either with our Heartland product or another in our RV life. I do the same thing but on no conditions do I walk away from the valve. As I recall, when it happened to me several years ago, it did not blow out the stink pipe either. I'm sure someone will chime in hear shortly with an answer.

 

[danemayer]

Hi Gary,

You probably have a 45 gallon tank. 10 minutes at 4.5 gallons/minute would just start pressurizing the tank. There's probably a few more gallons of capacity in the vent pipe.

A Watts 263A pressure regulator is only good for about 4.5 gallons/minute, and most regulators allow far less water flow. So you might not have gotten above 45 gallons in 10 minutes. Campground supply can also limit flow. I'd guess most places we go I'm getting maybe 3 gpm.

 

[Garypowell]

I probably need to restate as my first post was not clear enough. I think I was gone from the RV a good 20 minutes (I know really stupid) so I think the tank was pressurized for 10 minutes +.

The other two times (SOB's) I did this water started spraying out of the toilet and we heard the sound. On this Toilet (good or bad) it sealed so there was absolutely no leak.

 

[danemayer]

Well I don't know why, but now that your tank and your soul are both cleansed, go forth and sin no more - use a timer in the future.

 

[jayc]

I use my cell phone for a timer and have been using it for a couple of years. That way, it's in my hand, and so far it has worked.

 

[brianharrison]

A column of water exerts no more than 0.5 psi per foot of height (rounded, and if my math is right). Therefore even if the 8-10ft vent stack was completely full it would 'hold' no more than 4 to 5 psi in the tank. Certainly not 55 psi.

I cannot explain why it did not come out the vent stack on the roof if you did truly completely fill the tank. Maybe the vent stack covers are designed to allow gases but not water? I would doubt it, but I have never had one apart.

Brian

 

[Gizzy]

A column of water exerts no more than 0.5 psi per foot of height (rounded, and if my math is right). Therefore even if the 8-10ft vent stack was completely full it would 'hold' no more than 4 to 5 psi in the tank. Certainly not 55 psi.

I cannot explain why it did not come out the vent stack on the roof if you did truly completely fill the tank. Maybe the vent stack covers are designed to allow gases but not water? I would doubt it, but I have never had one apart.

Brian

Don't know about all this math stuff, but I CAN tell you from experience that it will (DID) come out of our vent stack.

 

[Ray LeTourneau]

After doing the same thing ONCE, I now do as Jay and use the timer in my cell phone if I start to do something else while flushing the tank. I use a device in the toilet that holds the ball open to get more air and when mine overflowed we had water on the floor and down the heat vent. Fortunately I had already dumped and flushed twice so it wasn't very "dirty" water. I still removed the basement wall and cleaned everything up and replaced the heater vent duct hose.

 

[mobilcastle]

That nearly happened to me!!! My DW came looking for me-my timer was set to long. From now on I am going to pull and turn on the flusher-I know that is not as good but nothing bad is going to happen. I don't want to clean up the mess!!! Way to go Ray!!


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[HornedToad]

I go wait inside the bathroom and listen to the tank flush,
you can hear when the water level rises over the spray valve
then it's time to pull the plug.

This routine keeps me from forgettin'!!!

 

[Garypowell]

Thanks all. I had not thought of the timer idea. When we started in 1996 we had beepers but now with smart phones this should be a slick idea. I also must confess that maybe Dan was right that we just caught it in time since there was no "geiser" and it was reported at least once above that someone has had it blow out the top.

Plus it helps to know I am not alone....well Linda is not talking to me yet but we will work it all out!

 

[JohnDar]

I don't leave the UDC when I'm dumping and flushing the tanks. If I'm running water up the sewer back flush, I use my watch or phone to time it. With the tank flush, I watch the water meter on my supply system if I close the valve.

 

[jbeletti]

Thanks for sharing Gary - now we can all confess and know we're not alone

I've done this, um, a few times. Once, I did have "stuff" running off the patio awning from the roof, from the black tank vent pipe. Yuck!

Why some don't do this - can't say for sure. You may want to test it though. With all 3 waste tanks empty, put a shut-off valve on the end of hose, turn the water on to the hose, take it up to the roof along with a screwdriver. Remove the cap of the black tank vent and add water into the vent. The vent should take water and my sense is that if the vent is still properly installed in the tank, the tank will take water and the vent will not overflow from the top (unless you run 45+ gallons down it).

If the vent take water but only for a short time, enough for the vent to fill, then I'd guess the vent has slipped down into the tank. You may even see this if you remove the vent cap and the PVC is lower than the roof deck. Worth at least looking at, if not tested.

 

[ramdually4100king]

Simple hydraulics. You have 50psi in a 1/2" hose. The vent is 2" in diameter with approx 14psi at sea level

F2=F1(A2/A1)
Where F2 is the force at vent
F1 is force at hose
A1 is area of hose
A2 area of vent

F2 = 50 * (.196/3.14) = 3.12 psi

Atmospheric pressure pushing down is enough to hold the water in the tank... Or as soon as a gallon of water (8.4lbs) filled the pipe there would be plenty force to keep water from gushing out the vent.

 

[Bobby A]

I go wait inside the bathroom and listen to the tank flush,
you can hear when the water level rises over the spray valve
then it's time to pull the plug.

This routine keeps me from forgettin'!!!

Ditto, been doing it this way for years, ever since I had my accident, I won't even answer a phone call when I'm in the middle of this operation. The key is to not get side tracked !!

 

[firemailwv]

I am soooooo glad to find out that I am not the only goober to have ever done this. I was too embarrassed to tell anyone and swore my camping buddies that witnessed it to secrecy! My mishap happened during setup. I hooked up the water hose to the campground faucet an then to the camper and turned the water on. Went on about my business setting the camper up outside while my wife was doing her thing inside. I was at the rear curb side jack and noticed a bit of water flowing out of the gutter. I thought it was odd that the AC was making that much water so quickly. About that same time - the screams began inside the camper as a geyser of water came out of the toilet when my wife flushed the valve! And I can confirm that it did make its exit out the top of the vent pipe.

I went to turn off the water and realized my mistake. I hooked the water hose into the black tank flush and not to the fresh water supply. To prevent me from making this mistake again, I purchased and quality quick connect setup which prevents me from hooking my supply hose into the flush connection.

 

[porthole]

Forget all the scientific equations and fancy math - I think ya got it just in time

Some people end up pumping it off the roof
Some people end up splitting their black tank

and some people are lucky

I would go as far to tell you - I have been lucky

 

[g.whisenhunt]

Instructions on my rig say if flushing water is on dump valve must be open