Abstract: A fluid operated pump for use in a vertical orientation includes an outer casing with a closure member disposed at one end thereof. A piston is operatively mounted for reciprocation within the outer casing and defines a first fluid chamber between the closure member, the outer housing and a first face of the piston. A first casing is provided at a point spaced from the closure of the housing. A second fluid chamber is formed between the outer housing, the first casing and a second face of the piston. A rod member is operatively disposed for reciprocation within the outer housing. The first piston member is affixed to one end of the rod member. A second casing is provided which is spaced at a predetermined distance from the first casing. A chamber is defined between the outer housing and the first and second casings. A plurality of tubes having inner and outer surfaces are disposed within the chamber and define a plurality of fluid passages between the inner and outer surfaces and the first and second casings.