Pneumatically drivable valve actuator and method of locking a valve closure element relative to a valve body

1. A pneumatically drivable actuator for setting a position of a valve closure element in a valve, comprising:

a piston, which is moveable in a pressure chamber by influence of a drive, gas;

a locking mechanism for mechanically locking the piston relative to the pressure chamber;

a first connector element connected to the piston, extending axially from the piston through an axial cylinder wall at least partly forming or enclosing the pressure chamber, presenting a connector that is accessible from outside the cylinder, and presenting, or forming part of a ventilation channel forming part of a ventilation device;

a second connector element, which is directly or indirectly connectable to the wall; and

the locking mechanism comprising a locking device, which is connectable to the first connector element and to the second connector element, such that relative movement between the piston and the pressure chamber is prevented in at least one direction;

characterized by

a ventilation device for venting the drive gas from the pressure chamber while the piston is mechanically locked relative to the pressure chamber, such that pressurization of the pressure chamber is prevented,

wherein the first connector element comprises, or forms part of, a channel forming part of the ventilation device.

2. The actuator as claimed in claim 1 , further comprising a transmission device for transmitting a movement of the piston to the valve closure element.

3. The actuator as claimed in claim 1 , wherein the ventilation channel is in permanently ventilating connection with the pressure chamber while the piston is mechanically locked relative to a wall of the pressure chamber.

4. The actuator as claimed in claim 1 , wherein the second connector element comprises a limiter device for limiting a movement of the piston.

5. The actuator as claimed in claim 4 , wherein the second connector element extends outwardly from an axial cylinder wall, and presents, or forms part of, the ventilation channel.

6. The actuator as claimed in claim 1 , wherein the locking device presents a connector that is interconnectable with the connector of the first connector element.

7. The actuator as claimed in claim 6 , wherein the locking device comprises a channel forming part of the ventilation device.

8. The actuator as claimed in claim 7 , wherein the locking device further comprises means for receiving a security lock, such as a padlock, for preventing unauthorized removal of the locking device.

9. The actuator as claimed in claim 8 , further comprising a sealing device, which is connectable to the pressure chamber, such that the pressure chamber is effectively sealed and relative movement between the piston and the pressure chamber is possible.

10. The actuator as claimed in claim 9 , wherein the sealing device and the second connector element present respective connectors for providing a sealed connection.

11. The actuator as claimed in claim 10 , wherein the locking device is at least partially integrated with the sealing device.

12. The actuator as claimed in claim 11 , wherein the locking device is mountable to the actuator only when the sealing device is detached from the actuator and vice versa.

13. The actuator as claimed in claim 12 , wherein the ventilation channel extends from the pressure chamber and along at least part of the first connector element, and

wherein the ventilation channel and the locking device are so designed that when the locking device engages the first connector element, the ventilation channel provides a fluid connection between the pressure chamber and the surrounding atmosphere.

14. The actuator as claimed in claim 13 , wherein the sealing device, which is connectable to the pressure chamber only when the locking device is not connected to the first connector member such that the pressure chamber is effectively sealed and relative movement between the piston and the pressure chamber is possible.

15. A method of locking a valve closure element relative to a valve body of a valve that is controllable by a pneumatically driven actuator, comprising:

mechanically locking a piston of the actuator relative to a pressure chamber of the actuator;

detaching a sealing device from the actuator to open a ventilation channel for providing said venting; and

mounting a locking device to the actuator, substantially at a position from which the sealing device was detached, such that the piston is mechanically locked relative to the pressure chamber,

whereby drive gas is vented from the pressure chamber, so as to prevent pressurization of the pressure chamber,

wherein the step of mechanically locking a piston of the actuator relative to a pressure chamber of the actuator comprises connecting a locking device to a connector element, which is fixedly connected to the piston and extends out of the pressure chamber, to provide said mechanical locking and maintain open the ventilation channel.