Abstract: A multi-stage pump system for use in desalination systems including a first stage S1 providing low pressure for priming the system a second stage S2 that is in fluid communication with the first stage and is primed by the low pressure from the first stage. The second stage S2B includes at least one reciprocating piston 122, in an enclosing cylinder 121, 121A and is attached to the two second flexible inflatable bladders 123. The piston 122 will move up and down within the cylinder 121 121A relative to the movement of the two second stage flexible bladders 123 due to priming by the first stage affecting their buoyancy. The driving fluid then passes into a passage 130 and is expelled to an outlet and Stage three (S3) at higher pressure when the first reciprocating member 122 proceeds through a complete stroke.

Abstract: A multi-stage pump system for use in desalination systems including a first stage S1 providing low pressure for priming the system a second stage S2 that is in fluid communication with the first stage and is primed by the low pressure from the first stage. The second stage S2B includes at least one reciprocating piston 122, in an enclosing cylinder 121, 121A and is attached to the two second flexible inflatable bladders 123. The piston 122 will move up and down within the cylinder 121 121A relative to the movement of the two second stage flexible bladders 123 due to priming by the first stage affecting their buoyancy. The driving fluid then passes into a passage 130 and is expelled to an outlet and Stage three (S3) at higher pressure when the first reciprocating member 122 proceeds through a complete stroke.