Hi Sajid,
It sounds as if you are interested in a large industrial-type
valve. The most interesting design considerations for the valve (and
the other components of your system) are missing from your question but
I can hopefully supply some of the issues that usually go into choosing
a valve:
1) How viscous is your medium? Is it watery or gooey or maybe does
it have gritty particles floating in it? To keep some delicate valves
clear of solid contaminants getting stuck inside, some valves have
filters attached to them. If you don't care about that, you may want a
valve with a closing mechanism that seals well even if some of it is
worn or has small particles in it.
2) How fast do you want your medium to go into and out of your
tank? This, plus the viscosity determines how big the valve should be.
3) How much pressure is in your tank? You can calculate the
"hydrostatic pressure" at a depth h from the top as the density*g*h
where g is 9.8 meters/sec**2, and density and h are in meters and kg,
which gives you pressure in Pascals. Most valves will handle many
atmospheres of pressure and shouldn't be a problem if the hydrostatic
pressure in your tank is all there is. But if your tank is pressurized
at even higher pressures then it is good to look at the valve
specifications. There may be leaks in the valve seat or in the threads
attaching the valve if the pressure gets too high. Please note:
hydrostatic pressure accumulates not only in the tank, but also if
there is associated plumbing connecting your valve to the tank. If your
valve is many meters below the bottom of the tank and attached by a
thin tube, then the pressure at the bottom of the tube is additionally
higher than that at the bottom of the tank.
4) Do you want any special features? Remote control? A big handle
in case it gets stuck and you have to pull hard? Fine control over flow
rate? Fine control over the pressure on the output side of the valve?
Fine control over the pressure inside the tank? These last two features
require special valves called "regulators", similar to those on scuba
diving equipment, which regulate the pressure sent out of the valve to
some other equipment or a person who needs the stuff coming out of the
valve. Valves that open automatically when the pressure in the tank
gets too high are called "relief valves" or if they are intended to be
usually operating, "reverse regulators."
There are lots of web sites associated with companies specializing in making and selling valves for all kinds of needs.
Tom
(published on 10/22/2007)
