MINIMIZING FRICTION Positioners minimize friction effects of valve stem packing and the resulting hysteresis. This is especially beneficial for high temperature packing materials like graphite.
INCREASES USAGE OF 4-20 mAELECTRONIC SIGNALS I/Ps can be located in the positioner that is on the valve. ACCURACY Positioners allow for fine control with better resolution and accuracy through full use of signal. This offsets the variation of the actuator’s range spring rate, which can vary ±8%. INCREASED RESPONSE TIME Positioners increase the response time to a change in the process. This allows for faster loading and venting.
NEGATES FLOW-INDUCED REACTIONS TO HIGHER PRESSURE DROPS This compensates for internal force imbalances. INCREASED FLEXIBILITY Permits use of piston actuators with high instrument air supply pressures.
SELECTION OF ACTUATOR BENCHSET RANGES THAT AREN’T MATCHING Positioners facilitate selection of actuator benchset ranges that aren’t “matching” or “multiple ratioing” from the signal. For example, using a 3-15 psig signal with a valve benchset of 10-35 psig signal. However, if the larger value of the benchset is above 15-18 psig, a positioner is technically required.
ALLOWS FOR SPLIT-RANGING This gives you the ability to use one controller for two valves; 4-12 mA and 12-20mA.
CHARACTERIZATION CAMS Positioners allow for incorporation of characterization cams to vary from the rotary control valve’s inherent character to a formed characteristic.
SEATING FRICTION Overcomes seating friction effects at travel below 10%, allowing throttling near the “closed” position in a rotary control valve.