Gas mixtures with a molecular weight less than 12 (specific gravity less than 0.4) are considered low molecular weight applications and must be reviewed by Ariel Application Engineering. A valid gas analysis must be provided for these applications. (When only a specific gravity is specified, the gas properties (K value and compressibility) used in the performance calculation are based upon a generalized hydrocarbon mixture. This could lead to inaccurate compressor performance predictions). The VMG gas method should be used for light molecular weight gasses.
Special attention will be paid to the selection of compressor valves for low molecular weight applications. The pseudo-Q-value must exceed 1.0 for all operating conditions. The application will be reviewed with the valve supplier to select the proper compressor valve. Ariel will also adjust the expected compressor capacity to account for higher piston ring blow by. It must be noted that any changes to the compressor valves that may be required to increase the pseudo-Q-value and any capacity adjustments may result in an increased HP (kW) requirement.
Applications that involve higher than 50% by volume of hydrogen shall be sized to limit the internal discharge temperature to 275 °F. Cylinders in these applications must have a helium leak test and packing cases with lapped cups.
Ariel
Corporation Application Manual
6-Sept-2001