A separator including a vessel, a tray assembly positioned within the vessel, and a wall structure arranged to accumulate a first liquid and a second liquid. A first automatic drain valve is operable to automatically allow liquid accumulated above a first liquid outlet to pass from the vessel in such a way as to maintain a volume of the first liquid above the first automatic drain valve to create a liquid seal over the first automatic drain valve, and a second automatic drain valve is operable to automatically allow liquid accumulated above the level of an open upper end of the wall structure to pass from the vessel in such a way as to maintain a volume of the second liquid above the second automatic drain valve to create a liquid seal over the second automatic drain valve.