Technical Reports, "Vacuum Brake Trials, May and June 1935, Direct Admission Valves (1) GWR Standard, (2) GWR Modified Comparison with (a) Electric Accel. Valves, (b) Std Arrangement ", 1935, London Midland & Scottish Railway, department, Chief Mechanical Engineers Drawing Office, Derby, format, typescript, number of pages 12, diagrams 9.