If the conveying medium of a fan must not be allowed to penetrate to the outside (e.g. gases that are harmful to health), our fans are equipped with a multi-chamber labyrinth seal on the shaft gland. Depending on requirements, the seals are provided with a sealing gas connection or a grease seal. Under certain circumstances the sealing gas can also be connected to the suction side of the fan. Naturally the flange connections are sealed accordingly and the fan housing is welded gas-tight and tested.