This invention provides a means to start an oil lubricated air cooled helium compressor at ambient air temperatures in the range from 30 C. to 0 C. by heating the oil in the sump and opening one or more by-pass valves that allows oil to flow to the oil injection port of the compressor without passing through all of the after-cooler.

A check valve provided makes it possible to operate a vane pump smoothly even at the start of the vane pump by maintaining an oil pressure in backpressure oil passages inside the vane pump while the vane pump is stopped. The check valve opens at the point in time when an oil pressure control device, to which a working fluid is supplied from the vane pump, has been filled with the working fluid and the oil pressure in discharge oil passages communicating with the oil pressure control device has risen and exceeded the oil pressure in the backpressure oil passages. Thus, the check valve is prevented from opening and closing repeatedly, so that the durability of the check valve is improved.

A drive unit (3) for a submersible oil pump, including a housing (7), a motor compartment (9) that is surrounded by the housing (7), and a rotor (13) arranged in the motor compartment (9), whereby a first fluid path (35) leading from a submerged oil environment (37) of the housing (7) to the motor compartment (9) is provided so as to allow oil to flow from the submerged oil environment (37) into the motor compartment (9).

A scroll compressor including a casing forming the exterior; a driving unit installed in the casing and generates a drive power; a rotary shaft installed in the driving unit to be rotatable; a compression portion including an orbiting scroll installed on the rotary shaft to be capable of orbiting, and a fixed scroll which is coupled to be engaged with the orbiting scroll so as to form a compression chamber between the orbiting scroll and the fixed scroll; and a check valve including a valve portion which is arranged so that one side thereof faces the compression chamber and guides suction of a refrigerant when being opened and is closed when the driving of the compressor is stopped so as to prevent the refrigerant from flowing backward, and a valve fixing portion which is installed on the side surface provided in the suction port of the fixed scroll.