From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Blueprint diagram comparing a bakelite disc valve and a ball valve for external pressure tests.
| Identifier | ExFiles\Box 151\2\ scan0064 | |
| Date | 11th April 1933 | |
| RELEASE VENTS ·320 .250 DIA BALL DISC VALVE BAKELITE BALL VALVE EXTERNAL PRESSURE "RECESSION" VALVE TESTS ROLLS ROYCE. LTD. PRINT ROOM APR 11 1933 DERBY. HS {Lord Ernest Hives - Chair} 981. 6-4-33 | ||