An apparatus comprising a first piston member (22) rotatable about a first rotational axis (30) and a rotor (16) comprising a first chamber (34a) and pivotable about a second rotational axis (32). The first piston member (22) extends across the first chamber (34a). The rotor (16) and first piston member (22) are rotatable around the first rotational axis (30), and the rotor (16) is pivotable about the second rotational axis (32) to permit a relative pivoting motion between the rotor (16) and the first piston member (22) linked to the rotor (16) rotating about the first rotational axis (30).

A screw compressor includes a screw rotor having a plurality of helical grooves, a first rotor configured to mesh with the helical grooves of the screw rotor, a second rotor configured to mesh with the helical grooves of the screw rotor, and a casing having a partition wall rotatably retaining the screw rotor and covering an outer peripheral surface of the screw rotor. The partition wall includes first and second envelope portions to form first and second compression chambers. The first compression chamber compresses a fluid introduced into the casing with a suction pressure to an intermediate pressure higher than the suction pressure. The second compression chamber compresses the fluid with the intermediate pressure to a discharge pressure higher than the intermediate pressure.

Disclosed herein is an indexing system for a rotor assembly where in one example the indexing system regulates the rotational location of drive rotors. In one example the rotors are configured to rotate about a shaft.

A screw compressor includes a screw rotor having a plurality of helical grooves, a first rotor configured to mesh with the helical grooves of the screw rotor, a second rotor configured to mesh with the helical grooves of the screw rotor, and a casing having a partition wall rotatably retaining the screw rotor and covering an outer peripheral surface of the screw rotor. The partition wall includes first and second envelope portions to form first and second compression chambers. The first compression chamber compresses a fluid introduced into the casing with a suction pressure to an intermediate pressure higher than the suction pressure. The second compression chamber compresses the fluid with the intermediate pressure to a discharge pressure higher than the intermediate pressure.

A screw compressor includes a screw rotor having a plurality of helical grooves, a first rotor configured to mesh with the helical grooves of the screw rotor, a second rotor configured to mesh with the helical grooves of the screw rotor, and a casing having a partition wall rotatably retaining the screw rotor and covering an outer peripheral surface of the screw rotor. The partition wall includes first and second envelope portions to form first and second compression chambers. The first compression chamber compresses a fluid introduced into the casing with a suction pressure to an intermediate pressure higher than the suction pressure. The second compression chamber compresses the fluid with the intermediate pressure to a discharge pressure higher than the intermediate pressure.

The invention provides a pump comprising a pump inlet, a pump outlet, at least two threaded rotors and a pressure controlled valve, the pressure controlled valve being capable of controlling re-circulation of fluid from the pump outlet to the pump inlet. The pressure controlled valve can be a control valve. The invention also provides a multiple stage pump assembly comprising at least two pumps arranged in series, wherein at least one of the pumps is the aforementioned pump.

A screw compressor includes a casing, a screw rotor accommodated in the casing to be rotationally driven, and a gate rotor assembly configured to rotate with rotation of the screw rotor. The gate rotor assembly includes a gate rotor including a plurality of flat plate-shaped gates configured to mesh with a helical groove of the screw rotor, and first and second support members. The first support member is made of a metal and includes a plurality of first gate support portions to support corresponding gates from a back surface side. The second support member is made of a metal and includes an annular portion having an annular shape and a plurality of second gate support portions each extending radially toward an outer side from an outer peripheral portion of the annular portion to support corresponding gates from a front surface side.