An apparatus (10), including a gas recirculation circuit comprising a mini environment chamber (14), a gas pump (16), a filter assembly (22) which are connected by a recirculation channel (20). The apparatus additionally includes an air supply conduit (18) for supplying air to the gas recirculation circuit and having an air supply conduit inlet (18a) which opens into the ambient air and an air supply conduit outlet (18b) which opens in the recirculation circuit. In use, a mini environment chamber pressure (Pme) is maintained higher than the ambient pressure (Pam). The gas recirculation channel (20) includes a substantially frictionless recirculation restriction embodied as a throat (30). At downstream end of the throat which forms the narrow part of the throat, in use, the static pressure is below the ambient pressure. The air supply conduit outlet opens at the downstream end (30a) of the throat.