The present invention relates to a membrane-based piston pump (400) for pumping a liquid product. The pump is provided with a device (426) for maintaining a pre-defined hydraulic fluid volume in the pump. The device comprises an axle element (440) and a bushing element (432). The invention further relates to a method for pumping a liquid product in a pump. Furthermore, the invention relates to a homogenizer provided with a membrane-based piston pump.

A reciprocating pump (10) comprises a first upright leg (12), a second upright leg (14), a first cross-over conduit (18), a second cross-over conduit (18), a lower valve assembly (20) and an upper drive assembly (22). The drive assembly includes plungers (30) which exert alternating downward pumping forces on columns of liquid in the legs (12, 14). The valve assembly is located in a reservoir of water (55) and includes suction openings (80, 64) in the water, which lead into the cross-over conduits (18) and (18), respectively. The valve assembly includes a system of valves and pistons (74, 76) for controlling flow of water into the legs (12, 14) via the cross-over conduits (12, 14) when pumping forces are alternately applied to columns of wafer in the legs (12, 14) wherein water in the legs is raised and lowered in alternating pendulum fashion. Water is drawn into and alternately forced along the cross-over conduits into the legs where the water is pumped from upper ends of the legs (12, 14) via slots (31) defined in the plungers.

A gradient high pressure syringe pump usable in a high pressure liquid chromatography system includes a housing defining an internal cavity, a drive piston, and a floating piston unconnected from the drive piston dividing the internal cavity into first and second pumping chambers. Each pumping chamber has an intake inlet with an upstream no-return valve communicating with a source of fluid and a discharge outlet communicating with an inlet of a downstream control valve. The control valve is operable to selectively direct fluid from either of the upstream pumping chambers downstream. In one embodiment, the first pumping chamber defines a cylinder section for the drive piston having an internal diameter smaller than the cylinder section defined by the second pumping chamber for the floating piston. The drive piston is moved linearly between suction and discharge strokes by an attached screw operatively coupled with a controllable stepper motor.

The invention provides an apparatus for compressing a first fluid. The apparatus comprises a compressor piston comprising a piston cylinder and a piston assembly slidably mounted therein. The piston assembly comprises first and second spaced apart piston members defining a space therebetween. The space is configured to contain a second fluid used to cause compression of the first fluid. The piston assembly further comprises means for feeding second fluid to the space between the first and second piston members.

A reciprocating pump (10) comprises a first upright leg (12), a second upright leg (14), a first cross-over conduit (18), a second cross-over conduit (18), a lower valve assembly (20) and an upper drive assembly (22). The drive assembly includes plungers (30) which exert alternating downward pumping forces on columns of liquid in the legs (12, 14). The valve assembly is located in a reservoir of water (55) and includes suction openings (80, 64) in the water, which lead into the cross-over conduits (18) and (18), respectively. The valve assembly includes a system of valves and pistons (74, 76) for controlling flow of water into the legs (12, 14) via the cross-over conduits (12, 14) when pumping forces are alternately applied to columns of wafer in the legs (12, 14) wherein water in the legs is raised and lowered in alternating pendulum fashion. Water is drawn into and alternately forced along the cross-over conduits into the legs where the water is pumped from upper ends of the legs (12, 14) via slots (31) defined in the plungers.

A membrane-based piston pump (400) is used for pumping a liquid product. The pump is provided with a device (426) for maintaining a pre-defined hydraulic fluid volume in the pump. The device includes an axle element (440) and a bushing element (432). A method for pumping a liquid product in a pump may use the membrane-based piston pump. A homogenizer may include the membrane-based piston pump.