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).
Analysis of a piston pump's operation, detailing the suction stroke, port registration, pressure dynamics, and its effect on the autovac system.
| Identifier | WestWitteringFiles\S\September1928-October1928\ Scan002 | |
| Date | 3rd September 1928 guessed | |
| contd :- -2- The pump - see LeC. 2470 and 2478 - has a stroke of .800" and we find the suction and outlet ports are separated by .600". When the piston port is in registration with the suction port i.e., the lower of the two ports, the piston will have completed .600 of its travel on the suction stroke. It then moves a further .200 to complete its stroke of .800 and so creates a small depression in the cyl. until the top of the piston uncovers the upper or outlet port, which it does at the bottom of its stroke. Air then flows into the cylinder under the depression caused by the latter .200 travel of the piston. The piston now ascends, raising the pressure in the cylinder until the piston port again registers with the suction port and so ejects air under this small pressure into the suction pipe which has the result of lowering the average suction. This appears to be the reason why greater autovac delivery is obtained with the non-return valve in the suction line to the autovac because when so situated it prevents this pressure discounting the suction built up in the autovac. We measured this pressure by disconnecting the autovac and having only the non-return valve connected with the suction pipe. A Mercury tube was connected with this suction pipe and would naturally only record pressure because the non-return valve opened under the lightest suction. In this way a pressure of .75" of mercury was recorded. We are wondering if there was any particular reason for this arrangement of the ports which we may have overlooked, as it seems to us that this has the effect of reducing the contd:- | ||