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Old 11-23-2020, 07:31 AM   #21
Montana Man
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It would be true about not causing any pressure on a Ridgid type of tank like steel or aluminum or something like that. But these tanks are plastic and expand and contract quite a bit. So when they are overfilled it literally pushes the top lid off of the tank
I have to disagree on how the tanks fail. When the tank is not supported on the bottom, it sags to the point of failing at it's weakest point due to deformation. There is no way to pressureize our tanks since they are vented. When filled, fluids simply back up into the tub or sink. It adds weight but doesn't pressurize per se as in an enclosed vessel. I've seen these tanks fail prior to reaching their fullest capacity thus eliminating the "pressurized" tank theory.
 
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Old 11-23-2020, 08:04 AM   #22
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I have to disagree on how the tanks fail. When the tank is not supported on the bottom, it sags to the point of failing at it's weakest point due to deformation. There is no way to pressureize our tanks since they are vented. When filled, fluids simply back up into the tub or sink. It adds weight but doesn't pressurize per se as in an enclosed vessel. I've seen these tanks fail prior to reaching their fullest capacity thus eliminating the "pressurized" tank theory.
I agree the tanks need to be supported from underneath. I've already done that to my three tanks
However if one continues to overfill it or travel with more than a couple few gallons in it you will sooner or later be replacing that tank
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Old 11-23-2020, 08:29 AM   #23
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Not made like they used to..
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Old 11-23-2020, 08:31 AM   #24
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Not made like they used to..
So you're saying they're made better now?

Brad
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Old 11-23-2020, 08:40 AM   #25
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Mike-- You are wrong about not overfilling the tanks. You can and yours if different entirely from the Dee Dub. Your tanks are one piece molded tanks where his are two piece tanks with a plastic weld and glue attaching the top to the bottom of the tank. The weld/glue is not strong enough to hold when to much pressure is applied inside the tank from overfilling it without the valve being open to let it drain. dfb's pictures show the tank that Dee Dub has and yours is one complete piece not two.

beeje-- the difference between the Legacy and the Montana is the front and rear cap, disc brakes, and the command center to start with. The Legacy is the new name for the Big Sky which was put out of commission several years ago. The new Montana's are the regular Montana from years back but without the back cap. The Montana High Country is now what used to be the Mountaineer.
2016 legacy... No disc brakes.. we got aluminum rims, observation camara, leveling system, rear cap.. no command center..
My black tank split at the seam....
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Old 11-23-2020, 09:43 AM   #26
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Sounds like to be a Master at Montana model identification all depends on what year(s) your familiar with.

As for pressurizing a tank ... it can be done at least on the FW tank. I've seen them swell up so far as to bulge the flooring above it. Depending on campground or your home water pressure, sometimes the vent won't handle the incoming flow.
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Old 11-23-2020, 10:21 AM   #27
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OP's original post has nothing to do with mounting, it has to do with what he stated filling and getting distracted. There is a post here some ware that deals with old and new tanks going POP. The technical part was that the vent being small, city water pressure being what it is and the size of the tank being what it is the pressure will soon exceeds the vents ability and pop either the vent on new tanks or in the old tanks the seam.
The recommendation was to put 2 minutes on your phone timer so as to not forget what you are doing, I do this because my Sometimers kicks in at the most in-opportune moments.

As for the Legacy package (don't forget hard wood cabinets), like some others have, at the right dealer (not Camping World), ordered everything except paint (including generator) and paid the un-optioned basic trailer MSRP.
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Old 11-23-2020, 11:17 AM   #28
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Wish we got the paint.. Gelcoat is such a pain ....
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Old 11-23-2020, 11:32 AM   #29
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OP's original post has nothing to do with mounting, it has to do with what he stated filling and getting distracted. There is a post here some ware that deals with old and new tanks going POP. The technical part was that the vent being small, city water pressure being what it is and the size of the tank being what it is the pressure will soon exceeds the vents ability and pop either the vent on new tanks or in the old tanks the seam.
The recommendation was to put 2 minutes on your phone timer so as to not forget what you are doing, I do this because my Sometimers kicks in at the most in-opportune moments.

As for the Legacy package (don't forget hard wood cabinets), like some others have, at the right dealer (not Camping World), ordered everything except paint (including generator) and paid the un-optioned basic trailer MSRP.
I believe this is the Post you remember. The same physics that push the water up the vent are also pushing the lid of the two piece tanks.


=====================================



https://www.montanaowners.com/forums...ad.php?t=80123 Post #12 and beyond


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.
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Old 11-23-2020, 12:35 PM   #30
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That's it. There are a few things that every owner should know and that is one of them.


As for paint, I thought long and hard about that and decided I could have someone detail it every year and not eat up that $10,500.00 in the years I will have this one.
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Old 11-23-2020, 07:24 PM   #31
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forget doing it yourself...pay the $1000 to a dealer.
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Old 11-23-2020, 08:07 PM   #32
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OK guys think about it. Do you really believe that a tank will burst when it fills then pushes water up 10 feet a 1 1/2" pipe? That's an extra 7.7 lbs. of water or about one gallon, on top of approximately 350 lbs. of water already in the tank. The previous post convincingly detailed a scenario in which the tank, within seconds, reached a pressure of 5000 lbs. That scenario may be applicable in a closed pressurized hydraulic system. However, in a vented system as is our tanks, it is static pressure.

When rinsing a black tank with the factory installed flusher, there is not enough volume of water entering the tank to overcome the volumetric air flow of a 1 1/2" vent pipe. All the tanks I've seen rupture did so previous to reaching full capacity.
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Old 11-24-2020, 03:00 AM   #33
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OK guys think about it. Do you really believe that a tank will burst when it fills then pushes water up 10 feet a 1 1/2" pipe? That's an extra 7.7 lbs. of water or about one gallon, on top of approximately 350 lbs. of water already in the tank. The previous post convincingly detailed a scenario in which the tank, within seconds, reached a pressure of 5000 lbs. That scenario may be applicable in a closed pressurized hydraulic system. However, in a vented system as is our tanks, it is static pressure.

When rinsing a black tank with the factory installed flusher, there is not enough volume of water entering the tank to overcome the volumetric air flow of a 1 1/2" vent pipe. All the tanks I've seen rupture did so previous to reaching full capacity.
My answer to your first question is yes I do. I am certainly not willing to find out. I will empty my waste tanks well before they are full and never travel with any more than a few gallons in them.
I have had the whole underside of my unit removed I know exactly what is in there and it would be a royal pain in the ass to change those tanks.
I think the whole point here is if you're going to use the black tank flush with the valve closed you better be paying a lot of attention to what you're doing
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Old 11-25-2020, 01:40 PM   #34
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We Used to fill our SOB to the toilet to clean the tanks out...
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Old 11-25-2020, 01:48 PM   #35
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Removing the Tank... 1. Remove the screws that hold the carpeted panel in place then slide the panel out of the way to access the pipes.. Drain and Vent.... 2. Cut pipes with sawzall or a hand saw.. 3.0 Remove the bottom to gain access the to tank. There are many Steel Nails that can be removed with pliars or a swazall again.. Replace with self tapping screws and washers.. 4. Disconnect the blade valve near the tank, cut the wires or remove wire nuts. These are for the Heater blanket and the level sensors. Unscrew flush out hose from tank.. 5. Loose the 4 7/16s boltsl hold one rail to the tank and slide it away from the tank.. Tank is light and will come down.. 6. Repair or Replace the tank.. When reinstalling the Vent and Drain pipe on top i used rubber boots and clamps so I would be able to remove in future... A new tank is 400 to 500.. However, the Drain and vent pipes must be reinstalled in the new tank.. Use a cloth or screen and ABS cement to repair... Above all.. Have Fun!!
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Old 11-25-2020, 02:41 PM   #36
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Removing the Tank... 1. Remove the screws that hold the carpeted panel in place then slide the panel out of the way to access the pipes.. Drain and Vent.... 2. Cut pipes with sawzall or a hand saw.. 3.0 Remove the bottom to gain access the to tank. There are many Steel Nails that can be removed with pliars or a swazall again.. Replace with self tapping screws and washers.. 4. Disconnect the blade valve near the tank, cut the wires or remove wire nuts. These are for the Heater blanket and the level sensors. Unscrew flush out hose from tank.. 5. Loose the 4 7/16s boltsl hold one rail to the tank and slide it away from the tank.. Tank is light and will come down.. 6. Repair or Replace the tank.. When reinstalling the Vent and Drain pipe on top i used rubber boots and clamps so I would be able to remove in future... A new tank is 400 to 500.. However, the Drain and vent pipes must be reinstalled in the new tank.. Use a cloth or screen and ABS cement to repair... Above all.. Have Fun!!
Are you knowledgeable about the above steps BECAUSE you filled your black tank up to the toilet to clean it?
Sorry, couldn't resist

Brad
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Old 11-25-2020, 07:39 PM   #37
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Old 11-25-2020, 07:58 PM   #38
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LEGACY MEANS YOU GET A REAR CAP, HIGH GLOSS GELCOAT FOR ANOTHER 6000! I do notice when selling the legacy nada or the dealers dont add even tho we paid for it!.. we get no better materials or construction and we get no add when
trading or selling..
Heated bathroom floor, solid wood faceframes on all cabinets instead of vinyl picture wood, rear cap and gel coat, Mor Ryde 4100 suspension and a Mor Ryde isolated pin box and seems I'm forgetting something else.


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Old 11-25-2020, 08:19 PM   #39
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OK guys think about it. Do you really believe that a tank will burst when it fills then pushes water up 10 feet a 1 1/2" pipe? That's an extra 7.7 lbs. of water or about one gallon, on top of approximately 350 lbs. of water already in the tank. The previous post convincingly detailed a scenario in which the tank, within seconds, reached a pressure of 5000 lbs. That scenario may be applicable in a closed pressurized hydraulic system. However, in a vented system as is our tanks, it is static pressure.

When rinsing a black tank with the factory installed flusher, there is not enough volume of water entering the tank to overcome the volumetric air flow of a 1 1/2" vent pipe. All the tanks I've seen rupture did so previous to reaching full capacity.
Quote:
Originally Posted by Montana Man View Post
OK guys think about it. Do you really believe that a tank will burst when it fills then pushes water up 10 feet a 1 1/2" pipe? That's an extra 7.7 lbs. of water or about one gallon, on top of approximately 350 lbs. of water already in the tank. The previous post convincingly detailed a scenario in which the tank, within seconds, reached a pressure of 5000 lbs. That scenario may be applicable in a closed pressurized hydraulic system. However, in a vented system as is our tanks, it is static pressure.

When rinsing a black tank with the factory installed flusher, there is not enough volume of water entering the tank to overcome the volumetric air flow of a 1 1/2" vent pipe. All the tanks I've seen rupture did so previous to reaching full capacity.
I see one of my previous posts was quoted, to which Montana man questioned it’s validity. The science of hydraulics is not disproved by “let’s think about it guys”....
The proof of that is Montana man’s thinking about it came to the wrong conclusion. The OP’s tank did fail while flushed with the drain valve closed. Not one drop of sewage exited the vent on his roof. The tank failed BEFORE the liquid got to the top! It didn’t fail while traveling, it didn’t fail because the vent pipe was blocked, it failed because the OP didn’t follow instructions to NOT flush the tank with the drain valve closed. Personally it think the warning label should offer the additional verbiage “ to do so you so, you assume all responsibility should the tank fail”. To return to my explanation, the black tank IS effectively a closed system up until the point the liquid has risen to the top of the vent pipe. A column of water exerts a back pressure equal to .434 psi for each foot of height. I used the example of a 10’ vent to make the math simple and easy to understand. The disconnect of understanding here is thinking a gallon on top of 350 lbs creates 5,000 psi. It doesn’t. What I am saying is the 5 psi of back pressure is multiplied times the total square inches of each of the tank’s 6 sides. The psi in the tank is not 5,000, the lifting force of 5 psi acting upon the total square inches of the top is pushing against the top and the bottom and is creating 5,000 lbs of force perpendicular to their plane. The formula is LxWxpsi= total force acting against a specific plane. Technically the semi supported tank bottom has the greatest force against it because it typically 6-8 inches lower than the top, Montana Is correct that the tank bottom is bearing the weight of water 8.33 X total gallons) but if the tank is filled to the point of water beginning to rise up inside the vent, every thing changes, and it does it in a matter of seconds! The 2 long sides are subjected the same force, but much less than the T & B. The two ends of the tank have the least perpendicular force. Hence the sides and ends of the tank would have a fraction of force acting against their respective planes compared to the top and bottom of the tank. Do tanks also fail due to not being installed improperly??? Yes they do! But not in the way the OP’s pictures show. IMHO flushing for more than 2 minutes either the dump valve closed is not only risky, but when the water covers the spray nozzle inside the tank, rinsing action ceases. Set an alarm on your smart phone for 2 minutes. Need more rinsing? Dump and start again.
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Old 11-26-2020, 03:46 AM   #40
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Agree!

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Originally Posted by kowbra View Post
I don't know about prior years, but the 2021 models use a 1 piece rotocast tank...
https://www.keystonerv.com/innovatio...-wheel-chassis

And, as to manufacturer recommendations, do you have info on where Keystone is not installing properly?

Thanks,
Brad
When on tour at the Montana factory last year during the MOC rally, I definitely recall them telling us that they now use all one piece tanks. If your coach is newer with a one piece tank and the sewer line is properly sealed and secure, the water/sewage should have come out the roof vent.not into the underbelly. That “pop” in my opinion was most likely an improperly sealed/secured sewer line to the tank. If indeed an older coach with a two piece tank, as already mentioned the top of the tank where the seam is could have split open as many suggested.
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