In adaptive seals such as brush seals, the performances is different from non contacting seals since leakage depends on a variable clearance. In the present experimental study of advanced seals the focus was directed at a combination of brush - and labyrinth seals. Experimental results are discussed for the configuration of two labyrinth teeth (upstream) and one brush seal (downstream). Special attention was paid to the gap between bristles and rotor using a new optical measurement method for small gap widths. An initial gap between brush and rotor is closed during operation of the rig by the so called blow down effect. In combination with leakage flow measurements it is shown how the pressure drop affects this blow down.
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