Physics Question (pressure and tank filling)

Gravity. A liquid exerts a force downward. To fill something further, you need a pump that will overcome that force. Is the force a liquid exerts purely a matter of pressure from the height of the liquid? Or does the volume of the liquid effect the force produced? Or is the pressure constant with height differential, and the force is pressure * surface area of the opening at the base?

Example: if you have a tank with a 1" diameter opening and it is filled 5 feet high, is the force needed to push more liquid in the same if that tank is 1" diameter all the way up as if it opens up to 3' diameter. Or will all that extra volume in the 3' tank exert a greater pressure?

Actual application: I am pumping beer out of bourbon barrels into our packaging tank. Unless I can borrow a fork lift and gravity-feed/siphon it, I will be using a small pump from our pilot system (I think it is 0.25 hp). I would prefer to fill from the bottom of the tank, but am concerned that the pump will not be able to overcome the weight of 90 gallons of beer. But, it will only have to push beer up a height differential of less than 3'. We use these pumps to do more than that regularly, but they only have to push beer through a 3/4" opening.

Here are your answers:

http://faculty.wwu.edu/vawter/PhysicsNet/Topics/Pressure/HydroStatic.html

It's column height. Width of the tank you are filling has no effect on pumping pressure required to fill it.

Yeah, test by seeing if your pump can pump beer up a clear hose 4 or 5 feet. If so, you're good.

Also, a lot of pumps have a head pressure rating. Usually measured in feet. You might check the specs of the pump.

Yep... volume has nothing to do with it. It is depth.

That being said, a small pump might be physically capable of moving the beer where it needs to be, but still take too long because of low volume.

Yep, Duke's right. Think of it sorta like working a floor jack; the pump moves fluid at a pretty decent pressure but a low volume. So you do get the work done but it takes longer. From what you describe, I'm going to say volume will be more important than pressure. Is it absolutely necessary to fill from the bottom, or can it be poured from the top? Pouring would be faster, assuming a larger opening and proper equipment of course.

You need a larger pump unless you want to spend all day pumping.

Cool. That's what I thought, but needed to double check.

The pump will move fluid up 5ft with no problem. I probably can't put too many pounds of head pressure on the tank though. It's decent speed. Should take me about an hour to transfer 90 gallons.

I am surprised a 0.25 hp pump is that slow. I've been playing with a variety of pumps for the past year for an irrigation project and you should be able to get a cheap pump that will do it in less than 10minutes

There are some waterfall pumps that you can find at home depot that put out like 30, 40+ gallons a minute. A lot of those would have 10 or 15ft of head though

if the barrel is higher than the container you are filling, then you will also get a "boost" from the siphoning effect once the beer starts moving.

Beer Baron wrote: Cool. That's what I thought, but needed to double check. The pump will move fluid up 5ft with no problem. I probably can't put too many pounds of head pressure on the tank though. It's decent speed. Should take me about an hour to transfer 90 gallons.

Heh, we've got a bunch of kegged up bourbon aged right now. I cannot WAIT to tap those bad mamma jammas.

fritzsch wrote: I am surprised a 0.25 hp pump is that slow. I've been playing with a variety of pumps for the past year for an irrigation project and you should be able to get a cheap pump that will do it in less than 10minutes

I'm extrapolating based on how long it takes to pump out 20 gallons of wort at the end of a brew cycle. That wort is more viscous, and has to be pumped through a plate heat-exchanger too.

It's also possible I'm remembering the HP rating on the pump, too.

Need a pump that will be gentle and NOT aerate the beer.

I used a diaphragm-type bilge pump to move some bulk reagents in a lab setting. Easy and fast.