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                               Plumbing lessons

My friend Kurt (same one I went haunted house hunting [1] with last year)
arrived to help help us movie. [2] He had just finished a class in checking
back-flow prevention valves, which is actually more interesting than it
sounds.

Kurt is currently a high school English teacher who is burned out—long hours
a poor pay have taken their toll on him, so he's getting into the family
business of plumbing. Only it's not plumbing as in plumbing repair, it's more
like plumbing engineering.

Between hauling boxes and furniture up to the apartment [3] he would stop and
explain how back-flow prevention valves work. Basically there are three
chambers. The first one is at a high pressure, say, 40 PSI. (Pounds per
Square Inch) It hits a plate separating the first and second chambers and
that plate has a spring holding it in place, but the spring has a much less
pressure, say, 5 PSI. That means the water from the first chamber enters the
second chamber but at a reduced pressure, which is the difference between the
water presure of the first chamber minus the pressure of the plate; in this
example, the water in the second chamber is now 35 PSI. There's another plate
between the second and third chambers, and this one supplies even less
pressure, say 1 PSI, so the water in the final chamber will only be 34 PSI.

Now, in the bottom of the second chamber is a diaphram, and water from the
first chamber is directly allowed to fill the area below the diaphram. This
pushes the diaphram up, because the pressure above is lower than below (35
PSI above, 40 below). Now, if the presure in the third chamber rises, it
shuts the plate, causing the pressure to rise in the second chamber. This
pushes the diaphram down, opening a valve to release the water directly out
of the system instead of letting it build up into the system.

Quite interesting. And you have to be careful in checking some of these back-
flow valves, especially the larger ones, as they can quite literally explode
in your face if you're not careful.

[1] gopher://gopher.conman.org/0Phlog:2000/08/11-15
[2] gopher://gopher.conman.org/0Phlog:2001/02/24.7
[3] gopher://gopher.conman.org/0Phlog:2001/02/24.8

Email author at [email protected]

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