It will have been a Chem dry or similar system , where there was ,in the old system a trolley with a CO2 cylinder ,and a stainless steel cylinder , holding the cleaning solution . The CO2 was used to both pressurize the stainless cylinder , and on earlier versions carbonate the solution . The theory was that the bubbles caused efforvescence , which blasted the dirt off the fibre being cleaned.
This system was devised by Robert Harris during a light bulb moment whilst he was on an aeroplane , and the flight attendant used soda water to remove a stain from his shirt.
At the time he was working as a security guard , and thought the carpet cleaners at the building where he worked were doing a crap job ,, so he rustled up some carbonated juice , cleaned the carpets , and Chem Dry was born .