Linear

Linear valve positioners are used on pneumatic linear actuators to control stem travel in control valves. The positioner compares the controller output signal with the actual valve position and adjusts the pneumatic output to the actuator in order to reduce deviation caused by packing friction, changes in differential pressure, diaphragm hysteresis, or mechanical tolerances in the feedback linkage.

This category includes linear positioners such as ARI STEVI-POS P20, OMC RE01, RE20L, RP01, PTL7L, and YTC / OMC YT series including YT-2300, YT-2400, YT-2500/2550, YT-2501, YT-2600, YT-2700, YT-3300/3350, YT-3301, YT-3303L, and YT-3400/3450. Available versions cover pneumatic, electro-pneumatic, and smart position control for single-acting and double-acting actuators.

The ARI STEVI-POS P20 is a digital electro-pneumatic smart positioner with a linear stroke range of 10-120 mm, instrument air supply 1.4-7 bar, G1/4 air connection, IP66 enclosure protection, and ambient temperature range from -20 to +80 °C. It supports 4-20 mA analog position feedback and fail-safe action by venting the actuator on loss of signal or air supply.

OMC RE01 units operate with a 4-20 mA input signal for analog control, while OMC RP01 units use a pneumatic 3-15 psi control signal. In both cases, the device compares the command signal with mechanical position feedback and modulates output pressure to the actuator. ATEX versions are available where hazardous area classification requires compliant equipment selection.

Smart positioners such as YTC YT-2300, YT-3300/3350, and YT-3400/3450 control valve travel from a 4-20 mA input and incorporate functions including auto-calibration, internal PID control, alarm outputs, and HART communication for commissioning, diagnostics, and maintenance.

Selection should be based on stem stroke, actuator type, available instrument air pressure, control signal, fail action, ATEX zone, air consumption, linearity, hysteresis, and accessibility for calibration and service. Maintenance typically includes inspection of air filters, nozzles, pneumatic tubing and fittings, feedback linkage condition, and deviation between setpoint and actual valve position.