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Old 11-21-2020, 09:15 AM   #41
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No!

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Originally Posted by Mr Towed;2454186[COLOR="Red"
]I’m sorry, I think your math is heavily flawed.[/COLOR] Pressure will not be multiplied by the area of the footprint of the tank, this is not a hydraulic cylinder we’re talking about. I fail to see the logic in that, I agree that there can be SOME pressure when the tank is overfilled and the overflow is too small to carry all the overflow, but some of it will come out of the IN as well,
I beg to differ. The math is correct.

What you are really questioning is the assumption of pressure that could be achieved during fill of a gravity fill tank.

If someone had a pressure-fill tank that was under-vented, those numbers would be achievable.
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Old 11-21-2020, 01:00 PM   #42
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Originally Posted by Larry-NC View Post
I beg to differ. The math is correct.

What you are really questioning is the assumption of pressure that could be achieved during fill of a gravity fill tank.

If someone had a pressure-fill tank that was under-vented, those numbers would be achievable.
In my original post i couldn't recall my old physic's class discussion on hrdrostatic pressures and "Pascal's Barrel" demonstration from 1646.

Old brain is slow and often requires some "google assistance".

As for an earlier comment regarding a hydraulic jack, the pressure inside it is the same in the pump as it is in the cylinder. What is multiplied is the amount of area it's applied to. In a jack the piston is designed to move so it lifts.

In a w
Water tank the inlet pressure, If outflow is blocked, will the max pressure of fluid but it's being exerted on all surfaces. Determine the entire area inside an RV water tank in square inches then apply whatever inlet pressure. Once the structural limits of the tank and supports are exceeded failure is a certainty.

The good news is that with fluids nothing explodes. The tank will fail and/or supports. The force is a lot more than just the 200-300 lbs of water in the tank. Don't try this with air.
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Old 11-21-2020, 01:03 PM   #43
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Originally Posted by Larry-NC View Post
I beg to differ. The math is correct.

What you are really questioning is the assumption of pressure that could be achieved during fill of a gravity fill tank.

If someone had a pressure-fill tank that was under-vented, those numbers would be achievable.
Not just pressure fill. How many people put the 3/4" hose fitting in the gravity fill port then open the water valve wide open?
I find it interesting that in plumbing electrical fields "conduits" that have to carry emergency discharges (drains and grounds) have to be sized to carry the maximum potential "flow". Could you imagine a drain that has the TPI valve discharging into ir being only 1/4 th the size of the discharge pipe"? How about using a #22 gauge wire for grounding a household electrical panel.

I've always wondered where they got the idea the small vent ports were enough on RV gravity fill ports given how tanks are most often filled.

Also, for those who put valves on pressure filled tank vents, make sure you NEVER forget to open it
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Old 11-21-2020, 03:22 PM   #44
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Originally Posted by TitanMike View Post
Have you ever seen air bags used to lift an overturned semi? They use air at less than 10 psi. The unit pressure doesn't increase but the amount of total force does.

Yes, i erred on the math but not totally on the force multiplication. More area, more force.
As for pressure being relieved through the fill pipe my example assumed that the fill was occluded by hose end and only the small vent was able to relieve pressure.
Right, my point is that no matter the surface area, volume, etc. the PSI is not going to increase. If there is 50 PSI supplied, that pressure will not increase above that level. I understand that every square inch has 50pounds applied to it, but that doesnít make it 57,000 PSI.
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Old 11-21-2020, 04:02 PM   #45
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I think strengthening the support is a good idea. However, I've been towing trailers with full water tanks for 55 years and have never had one fall out. But, if some day the bottom cover has to be removed I will certainly have it reinforced but I'll always carry plenty of water. We've had too many times over the years when we were glad we had it.
Yes since we mostly boon-dock besides the full tank I carry 3 jugs of fresh water totaling 18 gallons in the back of the truck to refill the tank as needed.
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Old 11-21-2020, 04:30 PM   #46
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Right, my point is that no matter the surface area, volume, etc. the PSI is not going to increase. If there is 50 PSI supplied, that pressure will not increase above that level. I understand that every square inch has 50pounds applied to it, but that doesnít make it 57,000 PSI.
I believe I revised my statement to reflect not Pounds Per Square Inch but to reflect the amount of WEIGHT that was being supported. In the example it is 57,600 lbs of total force in an area that totals 1152 square inches.

No denying that if that much force is applied to even the best of supports, something's going to break.

BTW I believe (recalling again some of my physic's classes) Pascal was told the same thing when he said the weight of a column of water would burst a barrel. He finally had to show them

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Old 11-22-2020, 02:42 PM   #47
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Water Tanks Falling Out

Yes it is a real problem. I added a strap across the center of my fresh water tank. The center had sagged several inches. Once I got a jack under the center and raised the tank so the center was flush with the floor, I drained two buckets of water from the tank. Donít know that the tank would have fallen out but I donít need to worry about it and it explains why Iíve been having problems with skanky water.
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