Accessories

A valve positioner receives a control signal (4–20 mA, 3–15 psi, or digital fieldbus) and continuously adjusts the actuator air supply pressure until the valve stem or shaft position precisely matches the set point. Positioners are required for any modulating (throttling) service - not just on-off - because they overcome packing friction, hysteresis, and spring non-linearity that would otherwise cause the valve to stop at the wrong position. Without a positioner, a valve may respond to a 50% input signal with anywhere from 40% to 60% travel, introducing significant process control error.

Analogue positioners use mechanical levers and springs to compare the control signal to the valve position and adjust the air output accordingly - simple, reliable, and immune to electrical noise. Smart (digital) positioners integrate a microprocessor, position sensor, and HART, Foundation Fieldbus, or Profibus communication module. They provide remote auto-calibration, partial stroke testing (PST) for ESD valves, valve signature diagnostics (detecting seat wear, actuator leaks, packing friction increase), and predictive maintenance data - all critical for modern digital plant management.

We supply mechanical limit switch boxes (cam-operated micro-switches, 2×SPDT, adjustable) and proximity limit switch boxes (inductive or reed contact sensors - non-contact, vibration-immune, no mechanical wear). All are available in IP67 weatherproof and Ex d / Ex ia ATEX-certified (Zone 1/Zone 2) versions. NAMUR-compatible mounting is standard. Visual dome indicators (green/red) are fitted on all models for 30 m line-of-sight position indication. HART-compatible smart position sensors are also available for integration with digital control systems.

Yes - any solenoid valve, limit switch, or electrical accessory installed in an ATEX Zone 1 or Zone 2 classified area must carry appropriate certification: Ex d IIC (flameproof) for Zone 1, or Ex ec / Ex nA for Zone 2. The gas group (IIA, IIB, IIC - where IIC covers hydrogen and acetylene, the most stringent) must also be specified. All Vajra solenoid valves for hazardous areas carry ATEX (EU) and IECEx (international) dual certification. Provide the area classification, gas group, and temperature class (T1–T6) when ordering for hazardous locations.