Solenoid Valves - 3/3-way valves | Hafner

Hafner 3/3 Solenoid Valves

The Hafner MH 331 G series are 3/3 solenoid valves designed for pneumatic circuits requiring a neutral position with a closed centre configuration. Upon loss of electrical signal, the valve returns to its mid-position via spring return, isolating all ports and maintaining actuator position under controlled conditions. Manual override is available for commissioning, panel testing, and functional checks.

Technical Specifications

• MH 331 701 G: G 1/4” port, flow rate 1250 l/min, pressure range 3–10 bar.
• MH 331 121 G: G 1/2” port, flow rate 3000 l/min, pressure range 3–10 bar.
• Operating medium: compressed air.
• Ambient/medium temperature: -10…+50 °C.
• Coil power consumption: 3 W DC / 5 VA AC.
• Switching time: 50 ms at 6 bar, +20 °C.
• Body: aluminium, G-series for inline or manifold mounting.

Closed Centre Function

The 3/3 centre closed configuration is used where pneumatic actuators must hold position without venting. Unlike 3/2 valves, the 3/3 design enables three states: supply, exhaust, and neutral isolation. This is critical for applications requiring controlled stop without depressurizing the actuator.

Valve Selection Criteria

Selection is based on:

• required actuator air flow,
• port size: G 1/4” or G 1/2”,
• available line pressure (min. 3 bar),
• requirement for closed centre on signal loss,
• coil voltage and connector type. Coils and connectors are not included with the base valve.

Industrial Applications

Suitable for pneumatic cylinders, packaging machinery, clamping stations, auxiliary automation circuits, and applications where actuator movement must be stopped without full depressurization.

Maintenance

Routine checks include air quality, leakage at exhaust ports, correct coil voltage, manual override operation, and condition of silencers or flow regulators at exhaust.