a draining apparatus drains and dries hydraulic equipment such as aircraft circuits . the draining equipment includes a reservoir connected to the equipment by a suction line . which produces a vacuum in the reservoir responsive to compressed air injected by a line from an external compressed air source . if a calibrated valve is connected to an inlet of the equipment then a branch line of the equipment supplies part of the compressed air to the inlet connection of the equipment so that pressure which enters the equipment is inadequate to produce an overpressure at an outlet .