Piston pumps or motors

In a multi-cylinder, reciprocating position type fluid pressure energy translating device in which there is relative movement between a cylinder block and a fluid handling section which defines internal, spaced, low and high pressure ducts, and in which such relative movement successively brings open ends of the piston chambers in the cylinder block into alternate open communication with the low and the high pressure ducts in the fluid handling section, and in which piston reciprocation and the relative movement between the cylinder block and said fluid handling section is timed so that each piston travels on at least a portion of its compression stroke between the time its chamber breaks communication with said low pressure duct and the time its chamber begins direct communication with said high pressure duct,

• pressure regulating structure for leveling pulsations in the high pressure duct including a ripple control capsule disposed in a chamber in communication with and only in communication with the high pressure duct,
• said capsule comprising a pair of spaced inner and outer porous wall members and a flexible, impermeable bag-like member disposed between said inner and outer wall members such that movement of said bag-like member is restricted by said inner and outer wall members, means for sealing the space within the bag-like member from the space outside of the bag-like member, and means for introducing fluid under pressure into said bag-like member,
• and wherein said capsule is so disposed in communication with the high pressure duct that the pressure in the high pressure duct is in communication with the space outside of said bag-like member such that pulsations in the high pressure duct are reduced.