Screw compressor with oil shutoff and method

A compressor comprising:

• a housing having a suction port (53) and a discharge port (58);
• a male rotor (26) having:
• an axis (500);
• a lobed portion (30) extending from a suction end (31) to a discharge end (32);
• a suction end shaft portion (39);
• and
• a discharge end shaft portion (40);
• a female rotor (28) having:
• an axis (502);
• a lobed portion (34) extending from a suction end (35) to a discharge end (36) and enmeshed with the male rotor lobed portion;
• a suction end shaft portion (41);
• and
• a discharge end shaft portion (42);
• a male rotor suction end bearing (96) mounting the male rotor suction end shaft portion to the case;
• a male rotor discharge end bearing (90-1, 90-2, 90-3) mounting the male rotor discharge end shaft portion to the case;
• a female rotor suction end bearing (98) mounting the female rotor suction end shaft portion to the case;
• a female rotor discharge end bearing (92-1, 92-2) mounting the female rotor discharge end shaft portion to the case;
• a lubricant flowpath (181;
• 281;
• 381;
• 481;
• 581;
• 681;
• 781);
• at least one valve (182;
• 282;
• 382-1,382-2,382-3;
• 82;
• 582-1, 582-2;
• 682-1, 682-2;
• 782-1, 782-2) along the lubricant flowpath and having an energized condition and a de-energized condition;
• and
• at least one restriction (184;
• 84-1,84-2;
• 84-1,84-2,84-3;
• 484-1,484-2,84-3;
• 84-1,84-2,584;
• 84-1,84-2,684;
• 84-1,84-2,784) along the lubricant flowpath,
• wherein the at least one valve is configured to:
• pass lubricant in a powered mode wherein the motor drives the rotors to compress fluid drawn in through the suction port and discharge the compressed fluid through the discharge port;
• and
• responsive to a loss of power produce a lubricant pressure difference biasing the rotors away from a discharge end of the case.

A method for operating a compressor, the compressor comprising:

• a housing having a suction port (53) and a discharge port (58);
• a male rotor (26) having:
• an axis (500);
• a lobed portion (30) extending from a suction end (31) to a discharge end (32);
• a suction end shaft portion (39);
• and
• a discharge end shaft portion (40);
• a female rotor (28) having:
• an axis (502);
• a lobed portion (34) extending from a suction end (35) to a discharge end (36) and enmeshed with the male rotor lobed portion;
• a suction end shaft portion (41);
• and
• a discharge end shaft portion (42);
• a male rotor suction end bearing (96) mounting the male rotor suction end shaft portion to the case;
• a male rotor discharge end bearing (90-1, 90-2, 90-3) mounting the male rotor discharge end shaft portion to the case;
• a female rotor suction end bearing (98) mounting the female rotor suction end shaft portion to the case;
• a female rotor discharge end bearing (92-1, 92-2) mounting the female rotor discharge end shaft portion to the case;
• a lubricant flowpath (181;
• 281;
• 381;
• 481;
• 581;
• 681;
• 781);
• at least one valve (182;
• 282;
• 382-1,382-2,382-3;
• 82;
• 582-1, 582-2;
• 682-1, 682-2;
• 782-1, 782-2) along the lubricant flowpath and having an energized condition and a de-energized condition;
• and
• at least one restriction (184;
• 84-1,84-2;
• 84-1,84-2,84-3;
• 484-1,484-2,84-3;
• 84-1,84-2,584;
• 84-1,84-2,684;
• 84-1,84-2,784) along the lubricant flowpath,
• the method comprising:
• running the compressor in powered mode wherein:
• the motor drives the rotors to compress fluid drawn in through the suction port and discharge the compressed fluid through the discharge port;
• and
• the at least one valve is in the energized condition;
• and
• terminating power so as to:
• terminate driving of the motor;
• and
• shift the at least one valve to the de-energized conditions to produce or leave a lubricant pressure difference biasing the rotors away from a discharge end of the case.