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Fail-safe position for double acting actuators

Fail-safe position for double acting actuators


Pressure loss, now what?

Realizing a fail-safe position for single acting actuators in case of pressure loss is easy. The integrated springs ensure that the actuator opens or closes.

The situation is different for double acting actuators. As they don't have springs, the actuator will stay or move to an undefined position in case of pressure loss.

The solution: using a control block in combination with an external air tank. Hafner offers the appropriate pneumatic solutions.  

Solution 1: Control block with 2 x 5/2-way solenoid valves

A double acting actuator can be controlled as usual via the Hafner control block. The actuator can be opened and closed by one of the two solenoid valves.

In the event of a compressed air and / or power failure, however, the control block also ensures that the actuator moves into its fail-safe position. The external compressed air tank provides the necessary air.

Fail-safe control

Solution 2: Valves with the NAMUR-interface for direct assemblage to the actuator


In the first solution, the actuator is controlled via our control block. However, if the actuator is controlled by another 5-way valve (e.g. from a control cabinet) or a positioner is used, our second solution is the best option.

These valves can be assembled directly to the actuator via the NAMUR-interface. If the actuator is controlled by a 5-way NAMUR-valve, this can be mounted directly together with our accessory valve. If a positioner is used or the control valve is installed externally, an additional threaded plate type GPN-1/4 is required.

In the actuated position, our valves allow the air coming from the 5-way pilot valve or positioner to pass freely to the actuator. In the event of an air and / or power failure, depending on the valve type, the connections to the actuator are exhausted. One of the two exhaust ports "R" can be used to move the actuator via the external air tank and thus move it into its fail-safe position.

Fail-safe control - NAMUR

The valves are also available made of stainless steel and for explosion hazardous environment

If you are interested in our solutions, please do not hesitate to contact us.


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