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Old 09-23-2012, 02:47 AM   #43
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Interesting problem with putting pressure into a rectangular prism - it tries to convert itself into a sphere.

Take a typical example of a RV tank say 50" x 30" on the flat side.

Imagine hooking the mains supply up to the tank and the tank has only a piddling 1/2" vent pipe. 100psi water at high flow rate blasting into the tank and trying to get out that small hole. Say the pressure inside the tank rises to 20psi.

The force generated upwards and downwards causing those flat sides to bulge - say 3" up and 3" down is 50 x 30 x 20 = 30,000 pounds
Damn near lift a whole class A off the ground all four wheels at once.

Sure, the mains pressure reducer should stop the pressure getting that high, but do the sums for even 10 psi and it runs into big numbers and big forces.

Even poking the hose down the gravity fill inlet - right down into the tank - to stop "burping" - and then turn the tap on full - can easily result in 4 or 5 psi in the tank and that will also bust restraining straps and even hardware store bolts.

Some fill systems use a restriction in the inlet line to keep pressure rise under control (and the regular RV inlet regulators include that), but lots of RV owners have nothing.

If you break mountings, it may not be the fault of the design
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Old 09-23-2012, 04:12 AM   #44
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Quote:
Originally Posted by wa8yxm View Post
Let's assume you fill the tank with water at an average temp of 60 degrees, as you drive it heats up to say 90 from sun on the RV. and expands.. Now your full tank explodes from the internal pressure.


Seriously now? I mean I have problems dodging falling comets too!

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Old 09-23-2012, 09:52 AM   #45
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Originally Posted by nightriderrv View Post
Well there are no baffles in the tanks with all that liquid and a evasive move on the road well you can get a slosh that can be bad and hard to control. You can keep some water to use on the road then top it off they are speaking from a safety factor
The effect you are referring to is worse with a partially or mostly filled tank. An empty or full tank won't exhibit this behaviour.
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Old 09-23-2012, 10:03 AM   #46
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Originally Posted by wa8yxm View Post
Let's assume you fill the tank with water at an average temp of 60 degrees, as you drive it heats up to say 90 from sun on the RV. and expands.. Now your full tank explodes from the internal pressure.
Water expands as it heats up?
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Old 09-23-2012, 10:15 AM   #47
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Originally Posted by RickO View Post
Frankly that warning surprises me. Seems to me that the "sloshing" causing a safety issue is a real stretch and so is using weight (as it contributes to GVWR) as the reason.

I know nothing of Jayco coaches but I wonder if they're concerned that the construction supporting the tanks might have a hard time hitting bumps with heavy tanks.

Rick
I second the motion! I would worry that they are telling you to be concerned about structure. I would contact the manufacturers technical support and find out why they are putting that out. I have in forty years of RV'ing never seen a manufacturer openly put out that kind of warning. I would check it out!

BTW; I travel with full tank of H2O and dump grey and black tanks as often as possible.
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