Low noise impeller pumps

An impeller pump comprising:

• a rotary impeller having a first surface and a second surface opposing to each other, wherein each of the first and second surface includes a plurality of grooves arranged in a circumferential direction of the impeller and spaced from each other by a predetermined pitch;
• a pump casing;
• a first pump channel defined in the pump casing and opposing to the grooves of the first surface of the impeller, wherein the first pump channel communicates with a first suction port and a first discharge port, and the first suction port and the first discharge port are separated from each other by a first partition wall;
• a second pump channel defined in the pump casing and opposing to the grooves of the second surface of the impeller, wherein the second pump channel communicates with a second suction port and a second discharge port, and the second suction port and the second discharge port are separated from each other by a second partition wall;
• a convergence channel communicating with the first discharge port and the second discharge port, so that the fluid discharged from the first discharge port and the fluid discharged from the second discharge port converge at the convergence channel;
• a pulsation canceling device arranged and constructed to cancel pulsations of the fluid discharged from the first discharge port and the second discharge port, respectively;
• an impact reducing device arranged and constructed to reduce impacts of the fluid caused by change of direction of at least one of a flow of the fluid discharged from the first pump channel toward the first discharge port and a flow of the fluid discharged from the second pump channel toward the second discharge port;
• and
• at least one communication hole defined in the impeller, the communication hole communicating between a pair of the grooves that are defined in the first surface and the second surface, respectively, and oppose to each other in an axial direction of the impeller;
• wherein the first discharge port and the second discharge port are formed separately from each other in the pump casing;
• and
• wherein the pulsation canceling device is arranged and constructed to displace the first discharge port from the second discharge port by a distance corresponding to half the predetermined pitch of the grooves of the impeller, and the grooves of the impeller defined in the first surface and the grooves of the impeller disposed in the second surface are disposed at the same positions in the circumferential direction of the impeller.