An upper piston and a lower piston are arranged in the housing.

The lower cylinder is adapted to receive the lower plunger and the upper cylinder is adapted to receive the upper plunger.

The plunger assembly includes a lower pressure chamber, an upper plunger element, and a lower plunger element.

The reservoir unit (20) has a piston assembly (70) with a top piston (72) and a bottom piston (74).

The piston assembly includes a driving cable connecting a top leaky piston and a bottom leaky piston having a check valve connected thereto.

An upper piston (9) and a lower piston (10) are respectively provided in the upper cylinder(6) and the lower cylinder (7), and the two pistons are connected together by a connecting rod(11).

The lower piston (21) is coupled by a connecting rod (25) to a crankshaft (13).

The existence of the intermediate segment inside the cylinder of the 'DOUBLE EXPLOSION PISTON' makes the bottom piston work in a four-stroke cycle also, ensuring identical performances as the upper piston.

The lower piston assembly includes a water supply tube (151) that engages a channel through the piston to supply heated water to the brewing chamber.

An upper piston (22) is axially movable in the upper cylindrical part (1) and a lower piston (6) is axially movable in the lower cylindrical part (2).

Said control system also regulates the opening and closing movements of the ports (7) of the lower piston (6).

Inner brake plates and outer brake plates alternately spaced each other locate between the upper piston and the lower piston.

The lower plunger and the ported valve cage define a production chamber within the pump barrel.

A brewing apparatus for a coffee machine comprises a brewing cylinder (6) and an upper plunger (3) and a lower plunger (4) forming a brewing chamber.

The relief valve structure (59) is wholly formed above the lower plunger (17), preferably within the upper plunger (13) above the timing chamber (26).