Control of supply of air to a pneumatic valve actuator

An assembly comprising a valve actuator and an actuator controller for controlling the function of the valve actuator, wherein the valve actuator is pneumatically operated, configured for being operatively connected to a valve, and comprises a cylinder and a piston movable inside the cylinder, the valve actuator has a pressure side and a non-pressure side separated by the piston, the piston is biased to be in a first position and is configured to move to a second position at a pressure increase on the pressure side of the valve actuator, and wherein the actuator controller comprises:

• a conduit connecting the pressure and non-pressure sides of the valve actuator for supplying the non-pressure side of the valve actuator with gas from the pressure side of the valve actuator,
• a control valve connected to the conduit between the pressure and non-pressure sides for controlling a release of gas from the pressure side of the valve actuator into the conduit, and
• a pressure-relief valve connected to the conduit to reduce the pressure in the conduit, the pressure-relief valve being positioned between the control valve and the non-pressure side of the valve actuator so that gas supplied from the pressure side of the valve actuator to the non-pressure side of the valve actuator during operation of the assembly flows from the pressure side of the valve actuator through the control valve and subsequently passes through the pressure-relief valve which directs the gas to the non-pressure side of the valve actuator.

A method of retrofitting a pressure-relief valve in an assembly comprising a valve actuator and an actuator controller for controlling the function of the valve actuator, wherein the valve actuator is pneumatically operated, configured for being operatively connected to a valve, and comprises a cylinder and a piston movable inside the cylinder, wherein the valve actuator has a pressure side and a non-pressure side separated by the piston, the piston is biased to be in a first position and is configured to move to a second position at a pressure increase on the pressure side of the valve actuator, and wherein the actuator controller comprises:

• a control valve for controlling a release of gas from the pressure side of the valve actuator, wherein the control valve comprises an inlet for being connected to a pressure source to receive a pressurized gas from the pressure source, a combined inlet and outlet, and an outlet, wherein the control valve has a first state in which the control valve leads pressurized gas from the inlet to the combined inlet and outlet and a second state in which the control valve leads pressurized gas from the combined inlet and outlet to the outlet, the assembly further comprises a first conduit section connecting the combined inlet and outlet of the control valve to the pressure side of the actuator, and wherein the method comprises:
• providing a second conduit section and the pressure-relief valve forming part of the second conduit section, and
• establishing a connection between the outlet of the control valve and the non-pressure side of the valve actuator with the second conduit section to position the pressure-relief valve between the control valve and the non-pressure side of the valve actuator so that during operation of the assembly the gas supplied from the pressure side of the valve actuator to the non-pressure side of the valve actuator flows from the pressure side of the valve actuator to the control valve and is then directed by the control valve to pass through the pressure-relief valve which directs the gas to the non-pressure side of the valve actuator,
• wherein the first conduit section, the control valve, the second conduit section, and the pressure-relief valve form parts of a conduit connecting the pressure and non-pressure sides of the valve actuator for supplying the non-pressure side of the valve actuator with gas from the pressure side of the valve actuator, wherein the pressure-relief valve is configured for reducing the pressure in the second conduit section.