How do diaphragm valves work?


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Old 12-04-05, 12:10 AM
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How do diaphragm valves work?

I know how they work. They shut of the water, but how do they really work. What physics allows water of the same pressure to actuate against a rubber diaphragm. What theoretically is actually happing in that diaphragm chamber?
 
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Old 12-04-05, 12:55 AM
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Are you reffering to a flushometer valve?

When you actuate the handle it breaks the seal between the upper and lower chamber (it unseats the diaphram), allowing water into the tailpiece. A small hole in the diaphram allows water to pressurize the upper chamber, forcing the diaphram to seat itself and stop the flush. Originally the valve had a bypass chamber built into the valve but was problematic because when debri clogged it, the valve would continually run.
 
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Old 12-04-05, 06:28 AM
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The physics involved are fairly simple once you see how any diaphram valve is built.

The diaphram is always bigger than the valve outlet. Regardless of the valve type (Flushometer, electric check valve, even a pressure reducing valve) there is a built in way for force to seal the diaphram. This force can be the same water going through the valve or it can be a handle with a spring. Regardless of force involved, there is just more area for the pressure to work on the diaphram, than the valve outlet, which will close the valve outlet.


I hope this is kinda clear...
 
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Old 12-04-05, 07:26 AM
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It is all a matter of area ( square inches) and pressure ( pounds PER square inch).

A good example is a solenoid operated irrigation valve. A rubber diaphragm blocks the water from the inlet, keeping the water from passing through to the outlet. A small passage, not larger than a pencil lead, also allows water from the inlet pipe to pass into a chamber on TOP of the diaphragm. Now we have equal pressure on top and bottom of the rubber; it should be free to float about at random. AHHHH.....but there is also a small spring pressing on top of the diaphragm. This extra pressure keeps it shut. It is all a matter of the DIFFERENTIAL pressure.

Now, to turn the valve on, the solenoid opens another small passageway allowing the water on top of the diaphragm to pass into the outlet port. ( Note that this passageway will be slightly larger than the passageway allowing inlet water into the chamber). As a result, the pressure in this chamber drops. Now the line pressure on the inlet side of the diaphragm is much greater than the spring pressure, so the diaphragm is pushed open and water flows to the outet.
 
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Old 12-04-05, 08:29 AM
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Originally Posted by 594tough
AHHHH.....but there is also a small spring pressing on top of the diaphragm. This extra pressure keeps it shut. It is all a matter of the DIFFERENTIAL pressure.

I have seen a lot of larger valves (6" and 8") thad don't have this spring. Brands are aquavalves, clavalve, ect.

Is it a matter of surface area or is it friction loss across the valve as it closes?
 
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Old 12-04-05, 10:55 AM
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A pressure of 100 PSI over a 6" diaphram will extert over 2800 pounds of force. But this same 6" diaphram fits on a 4" valve. The 4 inch line will have over 1200 pounds of force. It is an answer of square inches.

There are numerous variants of valves for all kinds of applications, but it is basically all the same principle.
 
 

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