A protection apparatus detects and reduces overpressure in a fluid pipeline. The positioning member is mounted under the lower returning section in a transverse direction transverse to a longitudinal direction of the conveyer belt. The honeycomb shells have application in slotted cylindrical projectors, flextensional projectors, inverse flex tensional projectors, and oval-shaped projectors in which the honeycomb structure replaces the solid shells, with the honeycomb providing the relatively high specific stiffness required for the acoustic properties of the projector. The at least one hydrophilic material includes either porous non-woven material or a porous membrane. A valve is disposed in the fluid passageway between the fluid outlet and the control valve.