OT: Physics/hydraulics of water and barrel

The same amount of pressure. From the bottom hole it has to lift it's diameter in water, and from the top it has to lift it's own volume of water in the hose up to the top so it can just gravity drop into the barrel. Same amount of energy required by the pump.

a bit easier to pump to the bottom bung, until the water level in the raised barrel rises. The fact that the hose has less volume of water than the barrel is irrelevant - it is the height you are pumping the water that matters.

but pumping to the top bung might prevent a problem if the hose comes loose.

That neglects the fact you're gonna get your ass wet when you go to disconnect the bottom hose, doesn't it? Where I hunted getting wet was not a pleasant prospect. In answer to the physics question, pressure is determined by the height of the water column where diameter (above some really small minimum) is irrelevant, so you actually need slightly less pressure to fill from the bottom if the top holes are on top of the tank rather than the sides.

O.K. At this point I admit I'm no doctor of physics. I also have to admit it was my idea to install the top fill bung thinking it would be easier to fill because I wouldn't be filling against a barrel full of water. So I lose the argument. HOWEVER... I also want to leave the hose attached to the top fill bung so I don't have to re-attach a water filled, running, hose back to the cabin.

Thanks!

O.K. At this point I admit I'm no doctor of physics. I also have to admit it was my idea to install the top fill bung thinking it would be easier to fill because I wouldn't be filling against a barrel full of water. So I lose the argument. HOWEVER... I also want to leave the hose attached to the top fill bung so I don't have to re-attach a water filled, running, hose back to the cabin.

Thanks!

LOL!

Water is heavy. How many PSI comes out that bottom hole?

The pump must first overcome this pressure before it can start filling the tank. That can easily mean the pump will 'run backward' and fill up the truck if the top tank has enough weight in it.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Jeepers wrote:

It will work. At my cabin (no electricity) we have a 500 gal drum on a

30 foot platform. It fills and drains through the same 1" hose. No problems at all.

Well, not quite. Moving the LAST slug of water requires the same amount of energy, but until the barrel is full, the water-column to the top bung is higher than the water colum to the botom bung and up the inside of the barrel. so the total energy used is LOWER if you pump through the botom hole.

--Goedjn

You can fill it from the bottom bung, top bung, or whatever. The pressure will be identical no matter where you fill it, until you start to raise the water above the level of the water in the barrel. You can get rid of that effect by running the hose over the lip of the barrel, and down to the bottom. As long as there is no air in the hose, the pressure is solely determined by the level of the water in the barrel.

If you want to fill the barrel through the bottom bung, you will want to have a valve to keep the water from running out through the pump and back into the barrel that's in the truck.

Ray Drouillard

Same for the top fill hole hose? Won't want to run backwards?

I'm gonna use the top fill hole anyway so I don't have to disconnect the drain hose from the cabin.

I lost the physics argument, but I had the right idea.

No way you lost the physics argument!

You asked which is easier? This means less 'work'.

If you had a real reservoir there and had 'say' for easy numbers 100 psi coming out the bottom pipe, then you 'first' have to build up 100 psi in the pump before the water will start to run back up that line. This takes power or 'work'.

If you have an empty line with no pressure in it the pump only has to hold the pressure of the water column in the pipe when filling from the top.

Yes if the tank was a void, then it would be lees 'work' to raise the water only to the bottom of the tank, but as soon as the tank has water in it, it is fighting back and the physics radically change!

So if you have a pump that can only generate 'say' 50 psi, then your truck tank will fill up at a rate of 50 psi out of that 'say' 100 psi line if there is no backflow valve.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Oh, great, now you've done it Ollie, I'm back to "confused".

Dude, you're babbling.

through the pump and

My physics is a bit rusty here, but IIRC, the pressure created at the bottom opening will be equal to the weight of a water column (which is the area of the opening x the height of the water column). This applies whether the bottom opening is at the side or on the bottom. A fluid exerts equal pressure against all sides of its container that it is in contact with. What this means in essence is that it would take slightly less energy to bottom fill. Any fluid in a container has some amount of stored energy, The wider and shorter the container is, the less energy it will take to fill it.

Also, like the others said, the energy required to top fill will remain constant as the barrel fills. For bottom filling, the energy will start out slightly less, and end up the same as the barrel reaches full.

Chris

O.K. my lame-ass attempt at physics argument:

Isn't part of the column the barrel? The barrel has a bigger column in it's part, than the hose. So the weight of the water column is GREATLY larger than the one in the hose going to the top. Less water - less weight, right?

I was clear, no hose over the top. 3 bungs on side of barrel, two at top, one at bottom. One top one is vent the other is fill.

Why isn't the additional water in the barrel not included as the static head on the lower fill? There is tremendously more volume in the barrel at, say half way.

Nope. When we speak of a column in this context, the column has the same area as the hose through which you're pumping fluid. If you wanted to know the pressure in pounds per square inch, you'd consider an imaginary coulumn with a cross-sectional area of 1 square inch.

The volume of fluid outside the column doesn't matter.

Consider this:

If you submerge yourself one foot under water in your swimming pool, you're subject to the same pressure as if you were submerged one foot under water in Lake Superior, even though the volume of Lake Superior is a gazillion times larger than your swimming pool (gazillion being a highly technical term used for these sorts of comparisons).

R, Tom Q..

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