Abstract
A brief account is given of tests carried out on air brake valves following concern over the performance of relay and load apportioning valves. Three load sensing valves, a Knorr, a new Wabco and a used Wabco, were taken through steps of input up to 8 bar. Input and output pressures were recorded and are presented in graphs. The old valve was 0.75 bar down on maximum output pressure but performed better at the most frequently used low pressures. None of the valves were ideal at low line pressures. At these pressures there was drag on the threshold making them more suited to some tractor/trailer configurations than others. The trailer control and relay valves tested performed well