Siemens Moore Products Series Model 74G Pneumatic Valve Positioners are universal positioners that provide versatility, dynamic performance, and high positioning accuracy. They use the piston or diaphragm in a pneumatic actuator to position a valve to what is required by a control instrument and hold that position, regardless of the presence of forces that change valve position. The Model 74G Positioners supply pressure variations have little or no effect on the positioner output, which eliminates the need for a supply pressure regulator.
These valve positioners are two-stage, pilot-operated instruments. The pilot circuit activates dual-output boosters, which perform opposite actions (when one booster is supplying air, the other is exhausting air.) This “push-pull” action applies to a full differential (supply pressure to atmosphere) across the actuator to drive the valve to the position required by the control instrument signal.
The Siemens Moore Model 74G Valve Positioners can also be used for single-acting service on a spring-loaded actuator. In this case, one of the pilot-booster connections is plugged.
As well as single-acting the Model 74G can be used for double-acting actuators, the output pressure level adjustment permits the pressure in the actuator chambers to be varied as desired. The optimum actuator pressure level setting for equal speed of operation in both directions is approximately 75% of supply pressure.
A key benefit of the Moore Model 74G Valve Positioner is that the field reversibility reduces downtime and simplifies maintenance.
There is a choice of continuously adjustable standard stroke ranging from 1/4" to 48" and continuous span and zero adjustability within range spring limits provide application versatility.
Extra high capacity pilots ensure maximum frequency response and optimum stroking speeds for all actuator sizes.
Negative feedback pilot circuit allows the positioner to operate with a push-pull gain of more than 900:1 (using 100 PSIG supply) with no sacrifice in stability (gain of 650:1 with 74S models).
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