Control Valve Accessories — Overview
A control valve is only as good as the instruments controlling it. Positioners ensure the valve reaches the exact position demanded by the control signal. Position transmitters feed back real-time valve position to the DCS/PLC. Air lock relays protect against uncontrolled valve movement during air supply failure.
KSB MIL Controls manufactures a complete range of accessories designed to work seamlessly with MIL series control valves — and compatible with other valve brands as well.
Product Range
MIL 8013 — Electro-Pneumatic Positioner
High-performance electro-pneumatic positioner that converts a 4–20 mA signal from PLC/DCS into precise pneumatic output to position the control valve. Force balance beam mechanism with flapper-nozzle system provides high dynamic response. Flexure bearings eliminate friction for exceptional sensitivity. Works with diaphragm and cylinder actuators. Direct and reverse action with split-range capability.
MIL 7400 — Pneumatic Positioner
Pneumatic positioner for all-pneumatic control loops without electrical signals. Maintains valve position proportional to the input signal pressure using a force balance mechanism with bellows and spring feedback. High sensitivity to small pressure changes. Bypass facility allows direct actuator control when needed. Available in standard and high-capacity pilot configurations.
MIL 400L — Electronic Position Transmitter
Inductive LVDT-based position transmitter that converts valve stem position into a proportional 4–20 mA DC output for PLC/DCS feedback. Non-contact sensing eliminates wear and friction — the movable magnetic core (armature) displaces within the LVDT coil without touching it. Two-wire system with field-reversible action. Zero and span adjustment via potentiometers. Suitable for both linear and rotary motion (via linkage).
MIL 776 — Air Lock Relay
Spring-loaded diaphragm relay that locks the air signal to the valve actuator during air supply failure, maintaining the valve in its last safe position. Prevents uncontrolled valve movement that could cause process upsets or safety incidents. Configurable for fail-close (FLDC) or fail-open (FLDO) modes. Bubble-tight shutoff. Can be panel-mounted or valve-mounted.
Product Comparison
| Parameter | MIL 8013 | MIL 7400 | MIL 400L | MIL 776 |
|---|---|---|---|---|
| Function | E/P positioner | Pneumatic positioner | Position transmitter | Air lock relay |
| Input Signal | 4–20 mA | 3–15 psi | Valve motion | Pneumatic |
| Output | Pneumatic | Pneumatic | 4–20 mA | Pneumatic (locked) |
| Accuracy | ±1% / ±2% | ±1% | <0.75% | — |
| Temp Range | -40 to +80°C | -50 to +80°C | -20 to +80°C | -20 to +80°C |
| IP Rating | IP65 | — | IP65 | — |
| Ex Rating | Ex ia / Ex d | — | Ex ia / Ex d | — |
| Action | Direct / Reverse | Direct / Reverse | Field reversible | FLDC / FLDO |
| Weight | — | 2.5 kg | 2.5 kg | 0.8 kg |
Typical System Configuration
In a complete MIL control valve installation, these accessories work together: the PLC/DCS sends a 4–20 mA setpoint signal to the MIL 8013 electro-pneumatic positioner, which converts it to pneumatic pressure driving the actuator. The MIL 400L position transmitter feeds back the actual valve position as a 4–20 mA signal to the DCS for closed-loop control. The MIL 776 air lock relay sits in the pneumatic line as a safety device, locking the valve in a safe position if air supply is lost. For all-pneumatic loops (no DCS), the MIL 7400 pneumatic positioner replaces the 8013.