or you could use valve gate, depending on the type of valve.

Control Temperature
... The purpose of the sensor is to control the precooler control valve butterfly ... resulting
force against the bellows causes the output rod to move the metering ...
digilander.iol.it/andreatheone/ctrltempeng.htm - 9k - Cached - Similar pages

Density controller system
... engine idle, oil pressure forces the exhaust bypass valve butterfly closed. ... At
this point, the pressure on the bellows begins to open the metering valve. ...
www.sacskyranch.com/turbo43.htm - 8k - Cached - Similar pages

Density controller and differential pressure controller system
... between sea level and the point at which the exhaust bypass valve butterfly ... The high
pressure above the diaphragm keeps the metering valve in the differential ...
www.sacskyranch.com/turbo42.htm


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Note added at 2002-08-08 10:06:17 (GMT)
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If you are not sure about the type of valve concerned, you can get out of it by saying \"valve diaphragm\"