Patent ID: 8535027

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 to the inner wall of the sealed main chamber and separated from the sealed main chamber so that the smaller chamber retains gas by trapping the gas within the smaller chamber, the smaller chamber having a passageway configured to be blocked by hydraulic fluid when the sealed main chamber is being filled with hydraulic fluid to trap the gas within the smaller chamber, the smaller chamber being provided with the passageway to permit fluid communication between the smaller chamber and the sealed main chamber to thereby accommodate thermal expansion of hydraulic fluid in the filled sealed main chamber.