The Type PN Pneumatic Piston Actuator is a ratio-piston-type actuator mounted on a reverse-acting gate valve. The PN Pneumatic Actuator is designed to be failsafe and fail-close. When installed as part of a safety system, it will automatically close with the loss of control pressure and will open automatically when the control pressure is restored.
- Actuators are used on secondary master valve and/or wing valve of a Christmas tree, flow lines, header valves, gathering lines and pipelines.
- As part of a surface safety system, the actuator will shut off flow from the well in the event of a catastrophic event.
- The PN surface safety valve is a pneumatic-controlled actuator that is operated by an air or gas source.
- Pneumatic pressure acting on the piston holds the valve open. Loss of pneumatic pressure in the actuator's cylinder allows the well or flowline pressure acting on the area of the lower stem to force the stem and gate closed.
- Pneumatic actuators can be used in both gas and oil wells. Care should be taken when using pneumatic actuators on high-pressure and/or large-bore applications.
- One of the opening characteristics of a pneumatic actuator is that once sufficient force is generated to break the differential, the valve will instantaneously go from closed to full open.
- This causes a slam-open effect that can cause damage to gates and seats. This can potentially damage the actuator. The following are some methods to reduce this potential problem:
- Reduce the differential pressure across the valve.
- Reduce the volume of air in the cylinder.
- Dampener mechanism.
- Use of a hydraulic actuator is considered the best option.
- Loss of control pressure above the piston will cause the actuator to close.
- In the event of a fire, the metal-to-metal seal between bonnet and lower stem acts as a secondary seal if the stem packing is damaged.
- Bonnet has a back-seat test port and packing leak detection port.
- A relief valve on the cylinder prevents over-pressurization.
- Large piston area permits use of low-pressure air or gas control systems.
- Rising stem for visual indication.
- Pneumatic cylinder and piston are electrolysis nickel plated for corrosion resistance, reducing repair cost.