A power assembly for obtaining duration discharge of product from a container, said power assembly comprising: a container cap (60, 240) attachable to an open end of said container; a cylinder cup mountable to said container cap (60, 240); a piston housing reciprocal in said cylinder cup; a piston carried by said piston housing for reciprocal movement therewith, said piston being in sliding sealed relationship in said cylinder cup and with said cylinder cup defining a pump chamber; the power assembly being characterized in that it further comprises: a rotatable drive screw (70, 70') extending into said piston housing; a rotatable actuator sleeve (90, 201) rotatably mounted on an upper end of said container; clutch means disposed between said actuator sleeve (90, 201) and said drive screw (70, 70'), said clutch means having an engaged position to rotate said drive screw (70, 70') when said actuator sleeve (90, 201) is rotated, and a disengaged position to enable rotation of said drive screw (70, 70') without causing rotation of said actuator sleeve (90, 201); first means (31, 76) engaged between said drive screw and said piston housing and second means (32, 51) engaged between said piston housing and said cylinder cup to cause said piston housing and piston to reciprocate in a first direction to draw product into said pump chamber when said actuator sleeve (90, 201) and drive screw (70, 70') are rotated; an energy storage device operable to store energy upon movement of said piston housing in said first direction, said energy storage device biasing said piston housing and piston in a second direction opposite to said first direction to pressurize the product in said pump chamber; a normally closed valve in fluid connection with said pump chamber to control flow of product from the pump chamber; and a reciprocal actuator (130, 230) that acts on said valve to open it and permit dispensing of product from said pump chamber when said actuator (130, 230) is depressed. a container cap (60, 240) attachable to an open end of said container; a cylinder cup mountable to said container cap (60, 240); a piston housing reciprocal in said cylinder cup; a rotatable drive screw (70, 70') extending into said piston housing; a rotatable actuator sleeve (90, 201) rotatably mounted on an upper end of said container; clutch means disposed between said actuator sleeve (90, 201) and said drive screw (70, 70'), said clutch means having an engaged position to rotate said drive screw (70, 70') when said actuator sleeve (90, 201) is rotated, and a disengaged position to enable rotation of said drive screw (70, 70') without causing rotation of said actuator sleeve (90, 201); first means (31, 76) engaged between said drive screw and said piston housing and second means (32, 51) engaged between said piston housing and said cylinder cup to cause said piston housing and piston to reciprocate in a first direction to draw product into said pump chamber when said actuator sleeve (90, 201) and drive screw (70, 70') are rotated; an energy storage device operable to store energy upon movement of said piston housing in said first direction, said energy storage device biasing said piston housing and piston in a second direction opposite to said first direction to pressurize the product in said pump chamber; a normally closed valve in fluid connection with said pump chamber to control flow of product from the pump chamber; and a reciprocal actuator (130, 230) that acts on said valve to open it and permit dispensing of product from said pump chamber when said actuator (130, 230) is depressed.