PLUNGER PUMP

PURPOSE:To reduce serging pressure and prevent generation of radiated noises caused thereby, by forming a sub-chamber in a cylinder, which sub-chamber is communicated with a suction port at a certain position during moving process of a plunger where a discharge pressure of a pump is an inner pressure in a cylinder chamber, and setting the volume of the subsidiary chamber so as to be required for reducing the serging pressure. CONSTITUTION:When a plunger 1 proceeds through a rotary cam 7, a suction port 3 formed on a peripheral wall of the plunger 1 is projected from an opening edge 2a of a cylinder 2, so that fluid is suctioned from the suction port 3 to a cylinder chamber 4. When the plunger 1 retreats, the suction port 3 is closed by an inner wall of the cylinder 2. Thus, the fluid is discharged to a discharge port 5 provided with a check valve 6 from the cylinder chamber 4. In such a setup, a subsidiary chamber 9 is formed in the cylinder 2, which sub-chamber 9 is communicated with the suction port 3 at a certain position in the retreating process of the plunger 1 where the discharge pressure of the pump is equal to an inner pressure in the cylinder chamber 4. The volume of the subsidiary chamber 9 is so set as to be required for reducing serging pressure.