A new technical document has recently been published and is now available from the National Fluid Power Association (NFPA).

ISO 6358-2:2013 (supersedes ISO 6358:1989) Pneumatic fluid power – Determination of flow-rate characteristics of components – Part 2: Alternative test methods

Scope: This part of ISO 6358 specifies a discharge test and a charge test as alternative methods for testing pneumatic fluid power components that use compressible fluids, i.e. gases, and that have internal flow passages that can be either fixed or variable in size to determine their flow-rate characteristics. However, this part of ISO 6358 does not apply to components whose flow coefficient is unstable during use, i.e. components that exhibit remarkable hysteretic behavior (because they can contain flexible parts that deform under flow) or that have an internal feedback phenomenon (such as regulators) or components that have a cracking pressure such as non-return (check) valves and quick-exhaust valves. In addition, it does not apply to components that exchange energy with the fluid during flow-rate measurement, e.g. cylinders, accumulators, etc.The charge test cannot be performed on components that do not have downstream port connections.

Benefits: ISO 6358-2 will help 1) a manufacturer determine characteristics for publication in a catalog, and 2) a system designer understand what the characteristics mean in order to compare pneumatic valves from various suppliers. The standard provides information superior to the traditional CV values.