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RE: [PSUBS-MAILIST] Pipe Diameter (was RE: payload)
NP,
You are correct in your assumptions in the static situation (i.e. none
moving fluids & equalized pressure). The caveat is when there is moving
fluid, there will be a small pressure drop across the orifice and if the
piping is long frictional losses will be a smaller pressure at the extreme
end from the orifice.
If you need to pump a fluid at high pressure, it takes a smaller piston.
The hydraulic jack is the perfect example, a small pistoned pump acts
against a larger cylinder. For each long stroke of the small piston the
large piston is raised a small distance and thus can move a large mass.
R/Jay
Respectfully,
Jay K. Jeffries
Andros Is., Bahamas
________________________________________
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Nomdae Plume
Sent: Friday, December 08, 2006 4:24 PM
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] Pipe Diameter (was RE: payload)
Yes. On a three square-inch surface area of the sub, that would be perfectly
true. But the pressure around the sub would not be changed: It would still
be 267psi.
The recent delay in the posting of emails (that, long with a few cups of
coffee) has me rethinking this whole thing. And Frank, if I've come across
in my emails as sounding condescending, I sincerely apologize. My intent is
not to challenge, merely understand.
Let me see if I can ask this a different way, and see what kind of answers I
get (and yes, I am looking for answers)
If I had a square tube welded to the side of my hull, and the opening was
exactly one inch wide by one inch high, and I had a square rod that fit
perfectly inside this tube, then when the sub is 600 feet down, them amount
of pressure I would have to exert on the rod (to keep it in place) would be
267 pounds because the end of the rod that is facing the ocean has one
square inch of surface area.
Now, instead of a 1 square-inch example, I perform the same experiment with
a ¼? tube & rod combination. The total amount of surface area facing the
ocean is a quarter of the surface area on the one-inch rod, so the pressure
I would need to keep this rod in place would be about 67 pounds.
Now, let?s set up a third experiment: Let?s use that same 1? square tube,
but this time we?ll weld a plate over the end (facing the ocean) that has a
¼? square hole in it. Now? how much force is it going to take to keep that
1? rod in the tube? My money would be on 267 pounds.
Here?s my idea of thinking: If you?re using a piston-type pump to force
water out of the sub into the surrounding sea, the amount of force required
is equal to the external pressure times the surface area of the top of the
piston. I don?t believe it has anything to do with the diameter of the pipe
between the pump and the hull of the sub.
Could someone tell me if I?m right or wrong on this one?
-- NP
________________________________________
From: bobtravis@comcast.net
Reply-To: personal_submersibles@psubs.org
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] RE: payload
Date: Fri, 08 Dec 2006 19:12:06 +0000
Wouldn't that be 267 pounds per squair inch? Which would mean that if you
had a surface area of three inches, then the force against it would be 801
pounds?
-------------- Original message --------------
From: "Nomdae Plume" <nomdae@hotmail.com>
Frank:
I read this post first thing this morning, and my brain still isn't in gear,
so let me see if I understand this correctly:
I'm in my sub, 600 feet down, and the outside pressure on the hull is 18atm.
(600 / 33) = 18.18atm or 267psi
Now let's say I have three pipes entering the hull, and all three have
pressure gauges on them. The first pipe is 3" in diameter, the second is
1", and the third is 1/4" in diameter. Won't all three gages read the same
pressure? Will a pump have to generate 267.0001psi in order to pump anything
out of the hull?
I think I can understand what you're saying about smaller pumps. A small
pump can be geared down so that the volume of water it's moving is decreased
while the pressure it creates is increased. It would just take more time to
pump out all the water you were trying to move. However, hooking a pump up
to a 1/4" hose is not going to give you any more of a mechanical advantage
than hooking it up to a 3" pipe... or directly to the hull of the sub.
Am I right? Or should I get a few more cups of coffee in me before I start
posting? ;-)
-- NP
________________________________________
From: ShellyDalg@aol.com
Reply-To: personal_submersibles@psubs.org
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] RE: payload
Date: Wed, 6 Dec 2006 21:30:09 EST
Just a quick note on this pressure thing. If you are pushing against the
pressure in a 1/4 inch high pressure hose/line, a small pump would work.
Frank D.
________________________________________
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