It's completely unclear what you are talking about. If it is pumps, well, if you need to pump gases, then that's what you pump. If you need to pump liquids, you pump liquids.
If, on the other hand, you are talking about fluid power devices in general, then there is machinery that relies on pumping gases; that's called pneumatics, versus hydraulic devices that pump liquids.
Hydraulic devices are preferred when large forces need to be generated in compact machines, meaning you need very high pressure differences. Designing such machines to work with gases would be impractical due to the compressibility effects of gases, which make the travel of pistons, say, highly dependent on the required force.