Patent ID: 8062010

Claim:
An assembly for a hydraulic pump comprising: a housing having an inner wall, the inner wall defining a periphery of a sealed main chamber; a pump port in fluid communication with the sealed main chamber; an aperture in the housing and a bearing disposed adjacent the aperture for rotatably supporting a rotor shaft which extends through the aperture into the sealed main chamber; and a smaller chamber fixedly attached . . . so that the smaller chamber retains gas by trapping the gas within a housing of the smaller chamber, wherein the smaller chamber is provided with only a single passageway, wherein the single passageway of the smaller chamber is configured to be blocked by a hydraulic fluid when the sealed main chamber is filled with the hydraulic fluid, the smaller chamber being provided with the single passageway to permit fluid communication between the smaller chamber and the sealed main chamber thereby accommodating thermal expansion of hydraulic fluid in the sealed main chamber.