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 the action of valve gear, plungers, and valves, focusing on oil flow and quiet running.
| Identifier | ExFiles\Box 17\6\ Scan304 | |
| Date | 4th September 1934 | |
| -3- When the valve gear rides, the plunger commences to move upwards under the action of the plunger spring and the plunger valve opens to relieve the vacuum thus created. In the case of the ball valve, the ball immediately falls through its maximum travel (about .006), displacing 10-4 cu.ins. of oil as it does so. This displacement is equivalent to an upward travel of .0003 of the plunger. If the movement is less than this no oil is drawn under the plunger, but any travel in excess of this amount must be accompanied by oil flow. In the case of the poppet valve, of which the permissible travel is much greater, a larger movement of the plunger can be compensated for by a downward travel of the valve for the same amount of oil flow. The spring load on the plunger valve is only 1-1 oz. so that the valve would move downward rather than the oil force its way past the small valve opening. 2. Slow Running. The criterion for quiet slow running is that the movement of the plunger in its casing should be as small as possible. Whereas the ball valve with large clearance is equally good as the poppet valve with small clearance from the point of view of maximum engine speed, it is worse for slow running. This is because the action of the mechanism is slightly different at high and low speeds. Ball Valve. Neglecting the 1st .0003 travel, every upward movement of the plunger is accompanied by an inflow of oil. This must be leaked out again if the plunger is to be restored to its former position. This applies at all speeds, and when slow running the necessarily larger clearance results in "dancing" plungers and noisy gear. | ||