What is ISO 6358‑2 - Pneumatic fluid power about?
ISO 6358 is a series on pneumatic fluid power. Pneumatic fluid power systems used in industry are commonly powered by compressed air or compressed inert gases. ISO 6358‑2 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.
Note 1: ISO 6358‑2 does not apply to components whose flow coefficient is unstable during use, i.e., components that exhibit remarkable hysteretic behaviour (because they can contain flexible parts that deform under the 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.
Note 2: ISO 6358‑2 does not apply to components that exchange energy with the fluid during flow rate measurement, e.g., cylinders, accumulators.
Who is ISO 6358‑2 - Pneumatic fluid power for?
ISO 6358‑2 on Pneumatic fluid power is useful for:
- Pneumatic component manufacturers
- Pneumatic machine manufacturers
- Design engineers
- Quality control personnel
Why should you use ISO 6358‑2 - Pneumatic fluid power?
In pneumatic fluid power systems, power is transmitted and controlled through a gas under pressure within a circuit. Components that make up such a circuit are inherently resistive to the flow of the gas, and it is necessary, therefore, to define and determine the flow-rate characteristics that describe their performance. ISO 6358‑2 was developed to determine the flow-rate characteristics of pneumatic valves, based upon a model of converging nozzles. The method included two characteristic parameters: sonic conductance, C, and critical pressure ratio, b, used in a proposed mathematical approximation of the flow behaviour. The result described the flow performance of a pneumatic valve from choked flow to subsonic flow, based on static pressure. ISO 6358‑2 uses stagnation pressure instead, to consider the influence of flow velocity on the measurement of pressures.
ISO 6358‑2 describes a set of three flow-rate characteristic parameters determined from test results. These parameters are described and are listed in decreasing order of priority that is the sonic conductance, C, corresponding to the maximum flow rate (choked) is the most important parameter. This parameter is defined by the upstream stagnation conditions, The critical back pressure ratio, b, representing the boundary between choked and subsonic flow is second in importance and the subsonic index, m, is used if necessary to represent more accurately the subsonic flow behaviour. Using ISO 6358‑2 you can specify a discharge test and a charge test as alternative methods for testing pneumatic fluid power components.
What’s changed since the last update?
BS ISO 6358‑2:2019 supersedes BS ISO 6358‑2:2013. BS ISO 6358‑2:2019 includes some technical changes with respect to BS ISO 6358‑2:2013. These include:
- An air source with a large flow-rate capacity is not required
- Components with larger flow-rate capacity can be tested more easily
- Energy consumption is minimized
- Test time is shortened in the discharge and charge tests, and noise level is decreased in the charge test
- Withdrawn standard
