Black tank failure

[rjlamb]

While using the Camco Blaster Pro tank flush adapter this morning, I experienced a major problem. Several minutes into the second filling, the black tank fractured its lid and water flowed everywhere. I removed the unit’s chloroplast underbelly and could reach up and lift the damaged section of the tank lid and reach inside the tank. My tank # is HT 543 from Keystone. My RV is a 2014 293RK HC. Where in the Palm Springs area should I begin looking for a replacement? If the roof vent on the tank is clear, how could pressure blow the tank?

[jcurtis934]

Pressure did no blow the tank! These tanks are known to be installed incorrectly by the tank manufacturer, who states not to support the tank by the lips around the top. The tanks expand a bit as they are filled, the top is sealed onto the molded bottom section and this forms the lips that keystone uses as the sole means of support. You can repair the tank with plastimend, but you need to either support the tank underneath in multiple places OR not fill the tank to capacity and never run the rinse port with tank closed.

[rjlamb]

The problem I am having is understanding how pressure from the city water can build up in the black tank when it has an inch and a half vent through the roof. I fully understand not paying attention to your flush procedures and having a giesser of effluent spouting from your rooftop vent!

[rjlamb]

Thanks jcurtis934 but pressure from the backwash procedure was most certainly the reason for the tank top splitting.

[DQDick]

A couple things to consider. 1st when you fill the tank completely up, floating stuff would have no problem finding the vent and plugging it up enough to stress the tank, 2nd the comments about how the tank is placed in there are right on and folks tend to forget what kind of weight is placed on a 50 gallon tank by water at 8.5# per gallon.

[rjlamb]

Thanks DQ
Both of your points taken. The tank let go in a wall of water. This took place
after draining black tank followed by draining grey followed by first city water flush of black and during the second city water flush it failed. Your floating effluent plug would explain the clogged vent but my back flush fill is usually three or four minutes long.

[Hblick48]

I use this to make sure I don't overflow my tanks when flushing:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

It measures water flow. Since I know by black tank holds 42 gallons, I usually fill it with 36 gallons and then drain. Do this until it drains clean. I use one of the clear plastic fittings:
https://www.amazon.com/Valterra-Degr...578848890&s=hi

This procedure ensures that I never overflow my black tank again. Don't ask how I know.

[twindman]

Good idea, Hblick. I use the standard Montana backflush and shoot for 4-5 minutes of rinse. I haven't had any problem except when I get distracted and let it run too long (new tank required twice!!!).

[Hblick48]

Originally Posted by twindman

Good idea, Hblick. I use the standard Montana backflush and shoot for 4-5 minutes of rinse. I haven't had any problem except when I get distracted and let it run too long (new tank required twice!!!).

When I replaced my black tank last summer, I decided not to install the flush wand into the side of my new tank. Just didn't want to drill a hole in new $500 tank. Flush wand didn't work that great.

[rustynail]

An easy way to make sure your tank does not overfill. Easy to get distracted by people and other things while flushing. I use the clock app and set timer for 5 minutes. No matter what you are doing alarm goes off and you know you have to empty. Works for me anyway

[Pitchbb9]

I need a new tank for my 2010 3400 RL
Where did you get your new tank?

[sptpfx]

Originally Posted by Pitchbb9

I need a new tank for my 2010 3400 RL
Where did you get your new tank?

I repaired mine. I made an and paste and used metal strips and plumbers strap for support.

[firestation12]

A hydraulic law every aspiring fire truck driver is taught: One pound of pressure will push a column of water (in a pipe) 2.3 feet high or to put it conversely, a column of water 2.3 feet high, exerts a pressure of 1 psi at it's base. With this knowledge, let's look at the problem posted i.e. the tank ruptured. Assuming a height of the tank's vent pipe opening being 10', the following applies: 10' divided by 2.3 equates to 4.348 psi at the top of the tank when the water exits the vent opening. Using a tank dimension of 24" X 48", the total square inches of the tank top is 1,152. Then if the 4.348 psi is multiplied times the square inches of the tank's top, we see that the total force applied is 5,008.896 pounds. At the point the tanks becomes full and the water is just at the point of entering the vent pipe, the tank pressure climbs from zero to 5,008 in just the short time it takes to fill the interior of the 1 1/2" vent pipe (maybe 5 seconds?). Lesson to be learned here is stay far, far away from over filling the tank. Another post by DQDICK suggested the possibility of a blocked vent pipe. Imagine if this scenario were to occur: the tank psi would be whatever the pressure of the source water supply. Thus 40 psi house pressure times the 1,152 square inches would equal 46,080 pounds of force on the tank top. If the object is to flush every surface of the tank's inside, perhaps a flushing wand inserted through the toilet would be a safer way. In my area, the house pressure is 80 psi. I would be uncomfortable running water for 5 minutes for fear I might overfill the tank. 3 minutes is my comfort limit when flushing, with an alarm set on my smart phone, and never l being further than reaching distance to the dump valve.

[Preston & Terri]

Originally Posted by firestation12

A hydraulic law every aspiring fire truck driver is taught: One pound of pressure will push a column of water (in a pipe) 2.3 feet high or to put it conversely, a column of water 2.3 feet high, exerts a pressure of 1 psi at it's base. With this knowledge, let's look at the problem posted i.e. the tank ruptured. Assuming a height of the tank's vent pipe opening being 10', the following applies: 10' divided by 2.3 equates to 4.348 psi at the top of the tank when the water exits the vent opening. Using a tank dimension of 24" X 48", the total square inches of the tank top is 1,152. Then if the 4.348 psi is multiplied times the square inches of the tank's top, we see that the total force applied is 5,008.896 pounds. At the point the tanks becomes full and the water is just at the point of entering the vent pipe, the tank pressure climbs from zero to 5,008 in just the short time it takes to fill the interior of the 1 1/2" vent pipe (maybe 5 seconds?). Lesson to be learned here is stay far, far away from over filling the tank. Another post by DQDICK suggested the possibility of a blocked vent pipe. Imagine if this scenario were to occur: the tank psi would be whatever the pressure of the source water supply. Thus 40 psi house pressure times the 1,152 square inches would equal 46,080 pounds of force on the tank top. If the object is to flush every surface of the tank's inside, perhaps a flushing wand inserted through the toilet would be a safer way. In my area, the house pressure is 80 psi. I would be uncomfortable running water for 5 minutes for fear I might overfill the tank. 3 minutes is my comfort limit when flushing, with an alarm set on my smart phone, and never l being further than reaching distance to the dump valve.

Wouldn't your calculation of 5008 pounds assume the 10 ft of height is 24 x 48 inches vs. what ever the 1.5 inch pipe (pi r squared?) area is? It's been a long time since I studied this but I seem to remember that pressure is constant?

[firestation12]

Diameter of the pipe is non sequitur. Depth of water creates the pressure. If you were a diver, you'd remember that for every 33' of depth, the pressure is 1 atmosphere or 14.7 psi. 33 divided by 14.7 = 2.24. this where the rounded off figure of 2.3 psi comes from.

[firestation12]

you are correct to say it is still only 40 psi, but the total force exerted against the top of the tank is 46,000 pounds of force. More than enough to cause failure. The figure GAinaMontana quotes of 7.4 psi exerted by a D6 cat is pounds per square inch, distributed over the area of the track. When the D6 runs over your foot, it's total weight no longer is equally distributed, but will be concentrated on that bump on the ground called your foot. I too pass on a D6 running over my foot!

[Gutz54]

Not to be a smart alec or anything--but can someone explain the easiest and safest method of cleaning out the black tank?? I don't know much about physics or PSI or pound /square mm.etc (LOL). When I empty my blcck and grey tanks and put the cap back on---the next time I take the cap off to attach the "******* " hose as my wife calls it about 3 gal of nasty stinking sewer water comes out-----does that mean the gate thing when I push it back in isn't completey closing off the black tank and it's defective???

[bigred715]

I had that same problem like everyone else until I bought the slide gate that fits on the end of the black dump pipe. The slide gate under the plastic cover doesn't always seal and thats why you have that ugly discharge when you take the end cap off. Took me too many years to figure out I needed that extra twist on dump slide.

[richeyb]

When flushing the black tank I make that my sole focus and rather than using the clock to judge filling the black tank I use the light gauge and fill it halfway then walk around and turn the water off. Haven’t totally filled it using the gauge. Guess if you gauge seems faulty this won’t work.

[firestation12]

Here's a link to a more in depth (pun) explanation of how a lesser pressure can lift a greater weight.

https://www.youtube.com/watch?v=UVEkJ7h1_Oo

Keep in mind, the weight of the car was supported by an area of 100 square inches. change that to the square inches of the tank's top, and it begins to make sense how the vent's 10' of elevation can create so much total force against the top.