From: BALLOONAIR@aol.com
Date: Tue, 22 Jun 1999 03:32:08 EDT
Subject: Re: 1000psi, how many balloons?
To: balloondeco@balloonhq.com
In a message dated 6/18/99 6:07:24 PM Eastern Daylight Time,
balloondeco-d-request@balloonhq.com writes:
<< If my tank reads a bit over 1000psi, how many 11 inch balloons can I fill
up? I know how many the whole tank fills up, but I don't know how to
calculate it after some of the tank has been used. Each balloon will hold
about .5cu ft. >>
Very simple. According to both my helium distributor and a PhD chemist
friend of mine, it is a direct proportional relation between the pressure and
the volume in the tank. In other words, when the pressure is half of what it
started out being, the volume of gas is also half. If your tank starts out
at, say, 2000 psi, and that is, say, 292 cubic feet, then when it hits 1000
psi you have half of that, or 146 cubic feet, which will do approximately 292
balloons.
Of course, in reality all the numbers are probably approximate. Your gauge
is probably not extremely accurate, and depending on how full they really
filled it, and what temperature it is at, it is probably starting out at
about 2200 to 2500 psi. Remember, this is the pressure, not the volume of
the tank. A smaller tank at 2200 psi will have less gas, let's say it has
100 cu. ft. @ 2000psi. When it is down to 1000 cu. ft. it also has half it's
original gas, so it has about 50 cu. ft. (In my mind I tend to use round
numbers, so if I start with a 110 cu. ft. tank at 2200 psi, I'm thinking to
myself that there's 100 cu.ft. @ 2000 psi, and that's 200 - 11" balloons,
while a 292 cu.ft. tank I think of as 300 cu.ft. or 600 balloons)
Different distributors have different names for the sizes of tanks they
carry. I've heard of T-tanks, K-tanks. 292's, Quite frankly I haven't spent
the time figuring out which is which. I prefer to know how much gas is in
the tank, in cubic feet. This is known as "minding your P's and Cubes".
Remember to do your math, or at least think about its implications. You
should know that a 9" balloon holds about .29 cu.ft. while an 11" balloon
holds about .5 cu.ft. The implications of this are: if you add 1" all the
way around a 9" balloon (making it 11" in diameter) you nearly double it's
volume. This means that a slight variation in size when you're inflating can
result in a tremendous difference in the number of balloons you're getting
from your tanks.
I didn't mean to go off on tangents again, but there I go. Anyway, assuming
you are inflating all your balloons to the same size, and the temperature
doesn't vary much, then your regulator gauge is a straight measure of what's
left in the tank.
O~ Danny Magowan
O~ : ) Balloon AffAIRs
O~ Syracuse NY
