Pneumatic power transmission. Flow characterization of pneumatic components

In pneumatic power transmission systems, power is transmitted by pressurized air or gas in a circuit. The components that make up such a circuit are intrinsically resistant to gas flow, and it is therefore necessary to define and determine the flow characteristics that describe their performance. Experience has shown that the characteristics of pneumatic components have much in common with either convergent or convergent-divergent nozzles, when frictional energy dissipation is negligible. Their flow characteristics can then be described from the knowledge of four parameters:

• sonic conductance C, corresponding to the maximum flow rate (sonic regime) ;

  the critical pressure ratio b, which represents the boundary between sonic and subsonic flow;

  the subsonic index m, which is used, if necessary, to represent subsonic flow behavior as accurately as possible.

• the parameter Dp _c , which characterizes the opening pressure. This parameter is only used for pneumatic components which open at increasing upstream pressure (threshold effect of non-return valves, for example).

When the effects of gas flow friction on tube walls or other components become non-negligible, then a fifth parameter is added, K _p , the pressure dependence coefficient.

After a brief review of the physical parameters inherent in pneumatic power transmission and their definition, we'll take a brief look at the laws of gas flow in ducts. We will then outline the "steady-state" measurement method, and comment on the requirements for the test facility and test procedure, the subject of Part 1 of the new ISO 6358 standard. The discharge and load test methods specified in Part 2 of ISO 6358 will be analyzed and commented on. Finally, the characteristics of each component and of the piping determined previously will be used to estimate the flow characteristics of an assembly.