Valve Positioners

A valve positioner compares the control signal with the actual stem or shaft position and adjusts the air pressure to the actuator until the two agree. Seven Star LLC supplies pneumatic, electropneumatic and digital valve positioners in Oman from Masoneilan, Fisher, Samson, Foxboro and Rotork.

The 27 listed items serve control valves and shutdown valves, and also include position transmitters, an electro-pneumatic transducer and remote position sensors.

Pneumatic, electropneumatic and digital valve positioners

Pneumatic positioners, such as the Masoneilan 4700P/4800P and 4200P and the Fisher 3610J, take a pneumatic signal and need no electricity at the valve. Electropneumatic units such as the Masoneilan 4700E/4800E accept a 4-20 mA signal directly. Digital positioners, also called smart positioners or digital valve controllers, use a microprocessor and add self-calibration, diagnostics and communication. Listed examples are the Masoneilan SVI3 and SVI FF, the Fisher FIELDVUE DVC6200 and the Samson TROVIS 3730-1. The Masoneilan SVI II ESD is intended for emergency shutdown valves and can run a partial stroke test while the valve stays in operation.

Choosing a positioner for an existing valve

Four things decide the choice. First the actuator: linear or rotary, single-acting (spring return) or double-acting, and its stroke or rotation angle. Second the signal: pneumatic, 4-20 mA, HART, FOUNDATION Fieldbus or PROFIBUS PA. Third the area classification, which determines the protection type needed, intrinsically safe or flameproof. Fourth the mounting: many positioners follow IEC 60534-6-1 (NAMUR) for linear actuators or VDI/VDE 3845 for rotary actuators, but a number of valve and actuator combinations need a specific mounting kit. Where vibration or heat at the valve is severe, a remote position sensor lets the electronics sit away from the actuator.

Information to send with a positioner inquiry

Give the full model code of the positioner if you are replacing like for like. For a new selection, send the valve and actuator make and model, stroke or angle, single or double acting, air supply pressure, input signal and protocol, the hazardous-area certification required, and any options such as position feedback, limit switches or gauges. We check the model code against the manufacturer documentation and can propose the manufacturer’s successor for an obsolete positioner, for sites across the GCC.