No, you can't increase the pressure of a water column by reducing the pipe
size anywhere in any direction. A 10 foot high cone with point at the bottom
develops exactly the same pressure at the bottom as a 10 foot high cylinder.
Also water pressure is exactly the same in a sideways direction as downward
at any given point. Any increase in force (pounds) can only occur with a
corresponding increase in area (square inches) so the pressure (pounds per
square inch) is constant. I am not sure but I think that is known as
"Pascal's Law".
Don Young

"PipeDown" wrote in message
ink.net...

"Harry K" wrote in message
oups.com...

PipeDown wrote:
"Chris Lewis" wrote in message
...
According to PipeDown :
Going from small to big won't cause much of a problem, aside from a
"if
you draw too much from one faucet, you might suck air in another"
factor.

You would never suck air into a fixture unless for some very unusual
reason
you were pumping warter out of another fixture at a rate greater than
the
source can replenish it. Excessive flow at one fixture would cause a
reduced flow at all other fixtures on the branch since all are
passively
powered by available water pressure. Only if a fixture were actively
accelerating the water would a negative pressure develop in the pipe
to
cause air sucking.

Heh, no, sorry.

Take a two story house with heavily restricted water feed. Turn on a
faucet
upstairs. Now, go turn on another faucet on downstairs.

Do you hear the faucet upstairs sucking air?

We do ;-)
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after
them.


Briefly said, gravity would be that additional accelerating factor.

Perhaps I was being narrow sighted since I am in a single story house
but
for that to happen the weight of the water column in vertical pipe
leading
upstairs would need to exceed the static water pressure minus that
pressure
relieved by the open downstairs fixture. In which case the 1/2" pipe
would
be advised due to the reduced weight of the water column. Such a
situation
should only occur in an installation flawed by inadequate water pressure
or
too large pipes for a given pressure/flow. I can also see that a
reducing
fitting an just the wrong spot on a vertical pipe could have unexpected
consequences by changing the static water pressure at that point (a
problem
which should not happen in a horizontal run because there is no pressure
gradient under static conditions)

Your reply may have been essentially correct but it sure was confusing.
I'm
not arguing, just trying to understand completely. In fact I am still
looking for a way to calculate the head pressure for each of the two
cases
of 10' vertical pipe 1/2" and 3/4" . While it is obvious that water in
a
3/4" pipe weighs more, the difference in area (of the pipe diameter)
would
yeild different PSI measurements which might be closer (i.e. mass is
distributed over a larger area in the 3/4" pipe). Maybe I'll post later
if
I can puzzle it out to my satisfaction, dosen't seem hard just short on
time
and willpower now.

No, a column of water 10 ft high will produce about 4.3 psi whether
that column is 1/2" or 5'. Seems counter intuitive but them is the
facts as I was taught in my last physics class ummmmm years ago .
Total weight of water depends on column size but the pressure per sq
inch doesn't change.

Harry K


Thats what I thought but a reducing union at the bottom would increase the
PSI by reducing the area while keeping the water column the same weight. A
reducing Tee would be OK as long as the size does not change in the
vertical direction