A separator for separating contaminants from a fluid stream, the separator comprising: a first inlet arranged to receive a first fluid stream including entrained contaminants, first and second separation stages (202, 206) coupled together in series and coupled to the first inlet to receive the first fluid stream from the first inlet and each arranged to separate contaminants from the first fluid stream, and a pump, in which one of the separation stages comprises a first variable impactor separator comprising: a first chamber arranged to receive the first fluid stream, a second chamber coupled to the first chamber through at least one aperture (66, 216) arranged such that the first fluid stream is accelerated through the aperture and is incident upon an impaction surface such that contaminants are separated from the first fluid stream, and an actuator (64, 212) arranged to adjust the open area of the at least one aperture, characterised in that: the second separation stage is a second variable impactor separator comprising:: a first chamber arranged to receive the first fluid stream, a second chamber coupled to the first chamber through at least one aperture (66, 216) arranged such that the first fluid stream is accelerated through the aperture and is incident upon an impaction surface such that contaminants are separated from the first fluid stream, and an actuator (64, 212) arranged to adjust the open area of the at least one aperture, the pump is coupled to the second variable impactor separator and arranged to generate an area of reduced pressure to draw the first fluid stream through the first and second variable impactor separators, the actuator (64, 212) is arranged to adjust the open area of the at least one aperture according to a pressure differential between fluid pressure in the first chamber and a reference fluid pressure in a third chamber. a first inlet arranged to receive a first fluid stream including entrained contaminants, first and second separation stages (202, 206) coupled together in series and coupled to the first inlet to receive the first fluid stream from the first inlet and each arranged to separate contaminants from the first fluid stream, and a pump, in which one of the separation stages comprises a first variable impactor separator comprising: a first chamber arranged to receive the first fluid stream, a second chamber coupled to the first chamber through at least one aperture (66, 216) arranged such that the first fluid stream is accelerated through the aperture and is incident upon an impaction surface such that contaminants are separated from the first fluid stream, and an actuator (64, 212) arranged to adjust the open area of the at least one aperture, a first chamber arranged to receive the first fluid stream, a second chamber coupled to the first chamber through at least one aperture (66, 216) arranged such that the first fluid stream is accelerated through the aperture and is incident upon an impaction surface such that contaminants are separated from the first fluid stream, and an actuator (64, 212) arranged to adjust the open area of the at least one aperture, characterised in that: the second separation stage is a second variable impactor separator comprising:: a first chamber arranged to receive the first fluid stream, a second chamber coupled to the first chamber through at least one aperture (66, 216) arranged such that the first fluid stream is accelerated through the aperture and is incident upon an impaction surface such that contaminants are separated from the first fluid stream, and an actuator (64, 212) arranged to adjust the open area of the at least one aperture, the pump is coupled to the second variable impactor separator and arranged to generate an area of reduced pressure to draw the first fluid stream through the first and second variable impactor separators, the actuator (64, 212) is arranged to adjust the open area of the at least one aperture according to a pressure differential between fluid pressure in the first chamber and a reference fluid pressure in a third chamber. the second separation stage is a second variable impactor separator comprising:: a first chamber arranged to receive the first fluid stream, a second chamber coupled to the first chamber through at least one aperture (66, 216) arranged such that the first fluid stream is accelerated through the aperture and is incident upon an impaction surface such that contaminants are separated from the first fluid stream, and an actuator (64, 212) arranged to adjust the open area of the at least one aperture, a first chamber arranged to receive the first fluid stream, a second chamber coupled to the first chamber through at least one aperture (66, 216) arranged such that the first fluid stream is accelerated through the aperture and is incident upon an impaction surface such that contaminants are separated from the first fluid stream, and an actuator (64, 212) arranged to adjust the open area of the at least one aperture, the pump is coupled to the second variable impactor separator and arranged to generate an area of reduced pressure to draw the first fluid stream through the first and second variable impactor separators, the actuator (64, 212) is arranged to adjust the open area of the at least one aperture according to a pressure differential between fluid pressure in the first chamber and a reference fluid pressure in a third chamber.