If high speed trains are going trough tunnels or there is oncoming traffic, strong fluctuations of the ambient pressure occur, which can reach up to ± 10.000 Pa. These pressure shocks would reach the inside of the pressure tight vehicle through the fresh air und exhaust air ducts of the HVAC system. With occurring pressure differences in the inside of the vehicle, people can suffer from an unpleasant feeling of pressure. Pressure protection systems consist of a pneumatic operated pressure-sealed fastening and an electronic differential pressure measurement, which in case of exceeding of limit values, give a signal for the pneumatic to close the mechanism.