849,301. Vacuum brakes. GRESHAM & CRAVEN Ltd., and MARSH, G. C. June 5, 1958 [Jan. 12, 1957], No. 18500/57. Class 103 (1). In a vacuum relief valve for braking apparatus atmospheric air is admitted to the vacuum conduit 40 at a branch piece 44 by the lifting of a valve closure member 19 to admit air through the strainers 33. The lifting of valve closure member 19, however, takes place as a result of the flexures of a diaphragm 21, subject on one side in chamber 13, to atmospheric pressure and the effect of spring 29, and on the other side through port 31 and by way of pipe 41 to the pressure in the conduit 40 as at port 43 remote from the branch 44. Such an arrangement gives an improved sensitivity and avoids faulty operation due to the disturbed pressure conditions resulting from the entry of air at a point near to the valve.