Adjective
Pertaining to, or depending upon, both liquid and gaseous substances; as, hydropneumatic apparatus for collecting gases over water or other liquids.
Source: Webster's dictionaryEngineering constraints The Indian Arjun MBT 's hydropneumatic suspension at work, while moving over a bump track. Source: Internet
Gordon Murray devised a " hydropneumatic suspension " system for the BT49C, which allowed the car to settle to a much lower ride height at speed. Source: Internet