The CPH model calibrated leak standard is available for several different gas types and mixes. It was developed to be compatible with ultra-high vacuum systems and other critical applications where out gassing and background signals need to be kept to a minimum.
The CP model calibrated leak standard, though typically used for helium, is also available for several different gas types and mixes. The difference is the shut-off valve on the CP model has a FEP valve packing that seals on the valve stem, in the place of the all-metal welded bellows model used on the CPH model. The CP model is an economical option that works well for most applications that utilize o-ring type vacuum fittings.
Both models are available with various sizes of DOT rated gas reservoirs. The reservoir size is usually dictated by the leak rate to insure an acceptable yearly depletion rate.