Oil seal arrangement

An oil seal arrangement for a cylinder containing oil, said oil seal arrangement comprising:

• a high-pressure seal mounted in said cylinder around a shaft inserted in said cylinder to seal a pressure chamber defined in said cylinder around said shaft, wherein said pressure chamber is filled with oil and positive and negative oil pressures are alternately produced in said pressure chamber;
• a low-pressure seal mounted in said cylinder around said shaft between said high-pressure seal and one end of said cylinder remote from said pressure chamber;
• and
• an oil seal chamber defined in said cylinder around said shaft between said high-pressure seal and said low-pressure seal;
• said oil seal chamber containing oil of the same type as oil in said pressure chamber, said shaft being completely submerged in the oil in said oil seal chamber and said oil seal chamber being sealed from outside a housing in which the cylinder is adapted to be fixedly mounted.

A pump, comprising:

• a housing;
• a motor mounted to said housing;
• a cylinder fixedly mounted in said housing, said cylinder having a bore;
• a rotary shaft rotatably mounted in said bore of said cylinder and coupled to said motor at a side at one axial end of said cylinder;
• a pump unit comprising rotary members disposed around and coupled to said rotary shaft at a side of another axial end of said cylinder, said rotary members being driven by said rotary shaft, thereby sucking and discharging hydraulic fluid in said housing;
• a first seal member mounted in said bore of said cylinder between said pump unit and said motor for sealing between an inner surface of said bore of said cylinder and an outer surface of said rotary shaft;
• a second seal member mounted in said bore of said cylinder between said first seal member and said motor for sealing between the inner surface of said bore of said cylinder and the outer surface of said rotary shaft;
• a seal chamber sealed from outside the housing and defined between said first and second seal members;
• and
• a hydraulic fluid of the same type as the hydraulic oil sucked and discharged by said pump unit, which is present in said seal chamber, said rotary shaft being completely submerged in the hydraulic fluid in said seal chamber.