Clarification of Actuator Pressure Rating and Maximum Working Pressure
The AWWA Standard C541-08 “Hydraulic and Pneumatic Cylinder and Vane – Type Actuators for Valves and Slide Gates” includes the following definitions.
Operating Pressure: The minimum and maximum hydraulic or pneumatic pressures, at specified operating temperatures, that an end user provides to operate an actuator. Usually the lowest possible minimum operating pressure available at the point of use is used for sizing actuators. Operating pressure is also referred to as “supply pressure” or “working pressure.”
Operating Pressure Rating: The minimum and maximum hydraulic or pneumatic pressures, at specified operating temperatures, that an actuator or cylinder manufacturer specifies to safely operate their products for optimum life.
Pressure rating: The maximum pressure that a manufacturer assigns to an actuator, cylinder or components that it can sustain without causing a catastrophic failure.
The proof-of-design testing for vane type actuators is established in the standard as follows:
Section 5.2.4 Quarter turn vane type pneumatic actuator: The proof-of-design test for a ¼ turn vane type pneumatic actuator shall consist of a life test of a production sample of each actuator size. The test shall be completed at greater than 90 percent full load torque in both directions for operation at the maximum recommended operating pressure for a minimum of 2 million operations. (An operation is defined as one movement of the actuator from one end of the stroke to the other). Failure of this test shall be defined as an inability to produce rated torque, excessive sideways movement of the output shaft (.008 in. maximum) excessive wear in the output shaft square drive, or failure of mounting interface. Operating ambient conditions will be 70 – 90 degrees F (21.1 – 32.22 degrees C).
As the industry leader and inventor of the rotary vane actuator, our position regarding the maximum operating (working) pressure is:
1. Kinetrol recommends using 80 – 100 PSIG air supply which will lead to optimum life of Kinetrol products. Kinetrol actuators far exceed the AWWA proof-of-design testing requirements. Kinetrol actuators can be operated at pressures up to 150 PSIG or even 225 PSIG, however, increased wear and tear on the actuator and valve will not lead to the optimum life (similar to running your car engine constantly at maximum RPM and expecting to get the same life as running it at normal operating RPM.)
2. Operating pressure Industries worldwide have used 80 – 100 PSIG to supply pneumatic actuators since they were invented. Most equipment that make up plant air systems, have been designed around this standard. Compressors run at better efficiency when operating at part load. A good rule of thumb is that for every 2 PSI increase over 100 PSIG in operating pressure requires an additional 1% in operating energy costs.
3. The operating pressure is always specified by the end user. Kinetrol will not encourage end users to produce more torque out of our actuators by asking for higher than normal (yes, the industry considers 80 – 100 PSIG normal) supply pressures. This is a game that some actuator manufacturers play who have limited torque ranges available and is not in the best interest of the end user. We have fifteen double acting models and over fifty spring return models available covering torques up to 168,000 inch-lbs. at 100 PSIG air supply.
4. All Kinetrol actuator models have been hydraulically pressure tested beyond 450 PSIG without failure of the housings. This provides a 3:1 safety factor between Kinetrol’s highest recommended operating pressure and the pressure rating as defined by the AWWA C541-08 Standard.
5. Kinetrol actuators are fully compliant with both AWWA C540-02 (old) and the new standard AWWA C541-08.
