(EP799380-A1)      The machine comprises a vertical cylinder (17), the lower end of which is open, with a piston (18) which vertically reciprocates in the cylinder. A water chamber (14) at the lower end of the cylinder has a water inlet (15) and a water outlet (16) which allows a flow of water. The flow is controlled by inlet (20) and outlet (23) valves.    The water inlet and outlet both open towards the periphery of the water chamber over the major portion of the chamber circumference with the inlet and outlet at different levels. The inlet and outlet valves comprises respective ones of a pair of annular valve members (21,24) which are concentric with each other and the cylinder and are axially movable between a closed and an open position.    ADVANTAGE -   Simple and inexpensive machine which is cheap to install and does not require extensive construction work.    (US5765375-A)      The machine comprises a vertical cylinder (17), the lower end of which is open, with a piston (18) which vertically reciprocates in the cylinder. A water chamber (14) at the lower end of the cylinder has a water inlet (15) and a water outlet (16) which allows a flow of water. The flow is controlled by inlet (20) and outlet (23) valves.    The water inlet and outlet both open towards the periphery of the water chamber over the major portion of the chamber circumference with the inlet and outlet at different levels. The inlet and outlet valves comprises respective ones of a pair of annular valve members (21,24) which are concentric with each other and the cylinder and are axially movable between a closed and an open position.    ADVANTAGE -   Simple and inexpensive machine which is cheap to install and does not require extensive construction work.    (JP10510900-W)      The machine comprises a vertical cylinder (17), the lower end of which is open, with a piston (18) which vertically reciprocates in the cylinder. A water chamber (14) at the lower end of the cylinder has a water inlet (15) and a water outlet (16) which allows a flow of water. The flow is controlled by inlet (20) and outlet (23) valves.    The water inlet and outlet both open towards the periphery of the water chamber over the major portion of the chamber circumference with the inlet and outlet at different levels. The inlet and outlet valves comprises respective ones of a pair of annular valve members (21,24) which are concentric with each other and the cylinder and are axially movable between a closed and an open position.    ADVANTAGE -   Simple and inexpensive machine which is cheap to install and does not require extensive construction work.    (EP799380-B1)      The machine comprises a vertical cylinder (17), the lower end of which is open, with a piston (18) which vertically reciprocates in the cylinder. A water chamber (14) at the lower end of the cylinder has a water inlet (15) and a water outlet (16) which allows a flow of water. The flow is controlled by inlet (20) and outlet (23) valves.    The water inlet and outlet both open towards the periphery of the water chamber over the major portion of the chamber circumference with the inlet and outlet at different levels. The inlet and outlet valves comprises respective ones of a pair of annular valve members (21,24) which are concentric with each other and the cylinder and are axially movable between a closed and an open position.    ADVANTAGE -   Simple and inexpensive machine which is cheap to install and does not require extensive construction work.