A vapor compression system comprising: a compressor ; a heat rejection heat exchanger coupled to the compressor to receive refrigerant compressed by the compressor; an ejector comprising; a motive flow inlet , a secondary flow inlet , an ejector outlet , a motive flow nozzle having an outlet , a primary flowpath from the motive flow inlet through the motive flow nozzle to the ejector outlet , a secondary flowpath from the secondary flow inlet to the ejector outlet , merging with the primary flowpath at the motive nozzle outlet , a control needle (200; 300; 400) shiftable along a range of motion between a first condition and a second condition and seated against the motive flow nozzle in the second condition, wherein the needle comprises: a main shaft , a tip , a first portion (220; 320) converging toward the tip, and a shoulder portion (214; 314; 422) between the first portion and the main shaft and seated against the motive flow nozzle in the second condition and converging toward the tip at a greater angle (θ l ; θ 1-2 ) than an angle (θ 2 ; θ 2-2 ) of the first portion; a heat absorption heat exchanger ; and a separator having: an inlet coupled to the outlet of the ejector to receive refrigerant from the ejector, a gas outlet , and a liquid outlet . a compressor ; a heat rejection heat exchanger coupled to the compressor to receive refrigerant compressed by the compressor; an ejector comprising; a motive flow inlet , a secondary flow inlet , an ejector outlet , a motive flow nozzle having an outlet , a primary flowpath from the motive flow inlet through the motive flow nozzle to the ejector outlet , a secondary flowpath from the secondary flow inlet to the ejector outlet , merging with the primary flowpath at the motive nozzle outlet , a control needle (200; 300; 400) shiftable along a range of motion between a first condition and a second condition and seated against the motive flow nozzle in the second condition, a motive flow inlet , a secondary flow inlet , an ejector outlet , a motive flow nozzle having an outlet , a primary flowpath from the motive flow inlet through the motive flow nozzle to the ejector outlet , a secondary flowpath from the secondary flow inlet to the ejector outlet , merging with the primary flowpath at the motive nozzle outlet , a control needle (200; 300; 400) shiftable along a range of motion between a first condition and a second condition and seated against the motive flow nozzle in the second condition, wherein the needle comprises: a main shaft , a tip , a first portion (220; 320) converging toward the tip, and a shoulder portion (214; 314; 422) between the first portion and the main shaft and seated against the motive flow nozzle in the second condition and converging toward the tip at a greater angle (θ l ; θ 1-2 ) than an angle (θ 2 ; θ 2-2 ) of the first portion; a main shaft , a tip , a first portion (220; 320) converging toward the tip, and a shoulder portion (214; 314; 422) between the first portion and the main shaft and seated against the motive flow nozzle in the second condition and converging toward the tip at a greater angle (θ l ; θ 1-2 ) than an angle (θ 2 ; θ 2-2 ) of the first portion; a heat absorption heat exchanger ; and a separator having: an inlet coupled to the outlet of the ejector to receive refrigerant from the ejector, a gas outlet , and a liquid outlet . an inlet coupled to the outlet of the ejector to receive refrigerant from the ejector, a gas outlet , and a liquid outlet . <EOS>