Patent ID: 7654806

Claim:
An external toothed wheel pump, comprising: a) a delivery chamber comprising an inlet and an outlet for a fluid; b) a first feed wheel and a second feed wheel which can be rotationally driven for delivering the fluid and are in a toothed engagement with each other which separates the outlet from the inlet; c) and sealing surfaces which axially face the feed wheels and form axial sealing gaps with the feed wheels, d) wherein at least one of the axially facing sealing surfaces comprises a relieving pocket on a high-pressure side of the delivery chamber only and except for the relieving pocket, extends circumferentially up to at least the root circle at the area of the relieving pocket and to the tip circle of the axially facing feed wheel elsewhere, e) wherein the relieving pocket extends counter to the rotational direction of the axially facing feed wheel, up into an enclosure formed by a radial sealing surface of the deliver chamber, and f) wherein the relieving pocket exhibits a distance in the rotational direction of the axially facing feed wheel from a plane extending through the rotational axes of the feed wheels and the distance measures e/2+−e/10, wherein e is the tooth gap width or tooth thickness of the axially facing feed wheel as measured to the pitch circle.