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Q & A: Valve engineering

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Most recent answer: 10/22/2007
Q:
What factors should be taken in consideration for desgining of Valve for storage tank, 16 M high, and 11.5 m dia, density of medium which will be stored is .9 g/ cubeic cm
- SAJID ALI (age 23)
UNITED FOODS CO, Dubai, UAE
A:
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)

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