Manufacturers of industrial process control gear keep the safety of their customers as a high-priority item when designing products. There is much at stake in industrial operations, so every instance where the probability or impact of failure can be reduced is beneficial.
Pneumatic valve actuators utilize pressurized air or gas as the motive force to position a valve. A common version of these air-powered actuators employs a rack and pinion gear set that converts the linear movement of air or spring-driven pistons to rotational movement on the valve shaft. When one side of the piston is pressurized, the pinion bearing turns in one direction. When the air or gas from the pressurized side is vented, a spring (spring-return actuator) may be used to rotate the pinion gear in the opposite direction. A “double acting” actuator does not use springs, instead using the pneumatic supply on the opposing side of the piston to turn the pinion gear in the opposite direction.
From time to time, service or maintenance operations for the actuator may require the opening of the pressure-containing case. This is a potentially hazardous step and confirmation that the case is not pressurized when disassembly is undertaken is essential to a safe procedure. Many pneumatic actuators have cases assembled with numerous threaded fasteners. Hytork, an Emerson brand, employs a keyway and flexible stainless steel key to affix the end caps to their XL Series pneumatic actuators. This method provides a number of benefits, not the least of which is preventing the removal of the key and end cap if the case is pressurized.