Abstract: A pressure relief valve for a railway emergency brake system that is simple in construction, easy to manufacture and to assemble and that, in operation, is self-cleaning of brake pipe dirt and debris. The inventive valve comprises a valve body having a hollow space being divided by a diaphragm into a first and a second chamber. Chambers are coupled via an orifice in the diaphragm, coupling pressure from the first chamber to the second. The valve comprises a peg aligned with the orifice, penetrating and cleaning the latter when the diaphragm moves from a closed position into an open position.