----- Original Message -----
From: Anthony L. Mourkas <frankenstein@TELPLUS.NET>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Thursday, August 19, 1999 8:34 PM
Subject: Re: More fridge help needed.

> >> So which is it?  Does one measure the difference in water levels from
one
> >> side of the "U" to the other after application of pressure?  Or does
one
> >> measure the total distance that the gas has lifted the liquid from a
zero
> >> point on one side of the "U"?
>
> >It is the difference in the height of the 2 columns, not how high one
column
> >rises.
> >You now have 22 inches of pressure in your gas lines, the way you did it.
> >Does your fridge light and how about the flames on the stove?
>
> Well thanks all for the science lesson.  Guess I had better perform that
> pressure adjustment again!!!
>
> I accept the decision but am still unclear as to the scientific
> explanation as to why it is the difference in column heights rather than
> the height difference in one column.  If anyone could educate me further
> my enquiring mind would like to know.
>
> Thanks,
>
> Tony
>
> 1984 Vanagon Westfalia
> Anthony L. Mourkas

Hi Tony

Well, here goes another explanation.

Suppose you measure the vertical height of the columns of water from the
very bottom of the U tube.  The left side which is open to the atmosphere
has a column height of 16 inches and the right side has a vertical column
height of 5 inches.  Now since the water is not moving anymore, the forces
in the water must balance, that is the force to the right must be exactly
equal to the force to the left.  So at the very bottom the forces are equal
as well.  What are the forces at the bottom?  Well look at the equation

Atm.  pressure + 16 inches of water  =  propane pressure + 5 inches of water

solving,

Atm. pressure + 11 inches of water = propane pressure.

By convention, only the difference of pressure is usually cited, which would
be the equivalent pressure exerted by a column of water 11 inches high.

Just for your reference, the atmospheric pressure is about 14.7 psi (pounds
per square inch) and 11 inches of water exerts a pressure at the bottom
of the column of about 0.40 psi.  the actual propane pressure is approx.
15.1 psi, but gauges usually measure the difference between actual pressure
and atmospheric.  Your tire gauges also measure the difference in the
pressures.

Hope this helps

Alfred