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Fig. C Back pressure Configuration Fully Closed
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Fig. D Back pressure Configuration Partially
Open
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| A back pressure regulator or relief valve controls
upstream pressure instead of downstream pressure. The control action in
the pilot is the reverse of the of a pilot for a pressure reducing valve
(increasing pressure in the sense chamber opens the pilot valve). At no
flow, when the inlet pressure is less than the set point of the pilot
regulator, the pilot is closed and full inlet pressure loads the spring
case through the pilot loading connection. In this condition, the diaphragm
is closed tightly against the throttle plate. The pressure differential
across the outlet half of the diaphragm adds to the spring force in closing
the FLOWGRIDtm VALVE (refer to Figure C). As inlet pressure increases above the set point of the pilot regulator, it will open and start bleeding pressure out of the spring case faster than it can enter through the restrictor. |
Reducing the pressure above the diaphragm allows
inlet pressure to progressively lift the throttling element off the throttle
plate opening the valve and satisfying the demand for flow in the upstream
system (refer to Figure D). When upstream pressure decreases, causing the pilot regulator to close, pilot supply pressure continues to pass through the restrictor until the control pressure equals the inlet pressure. The spring force, plus the pressure differential across the outlet half of the throttling element closes the diaphragm against the throttle plate, shutting off the flow (refer to Figure C). Adjustment of the restrictor affects the response rate, stability, and sensitivity of the regulator. Smaller restrictor openings result in higher gain (sensitivity) and slower closing speeds. Larger openings result in lower gain (greater proportional band), greater stability and faster closing speeds. |
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40 West Gregson Ave. Salt Lake City, Utah 84115 Phone: (801) 487-2225 FAX (801) 487-2587 E-MAIL: mail@mooneycontrols.com 
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