A cold ejector is used to pump the helium inside 3 large operational cryopump systems at JET to a pressure below the suction pressure of the cryoplant compressor (160 gs­1/1.3 b absolute) down to 250mb below atmospheric pressure. The cold ejector has been successfully operated for over 2 years and successfully copes with stringent dynamic conditions encountered during cooldown and cryopump regeneration. The performance characteristic of the cold ejector has been analysed by calorimetric measurements with a power of up to 300W and for flow rates of up to 60 gs­1. The pumping of gas, vapor and liquid have been compared. The results are presented and operational aspects discussed.