Air Driven Liquid Pump The air driven liquid pump is pneumatically driven reciprocating piston pumps. These air driven liquid pumps are proportional devices that utilize low pressure compressed air to drive a larger diameter piston (area x pressure) that is linearly connected to a smaller hydraulic piston/plunger. Utilizing this ratio principle, higher hydraulic pressure can be generated. Materials of construction include standard all stainless steel wetted ends and polyurethane pressure seals. Specialized materials of construction and special seals are also available upon request. Compact and lightweight, this air driven liquid pump requires no air lubrication and is suitable for water, oil and most chemical applications.