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 pump performance including pressure fluctuations, carburetter feed, tilting, and hand operation.
| Identifier | ExFiles\Box 77\4\ scan0010 | |
| Date | 26th April 1917 guessed | |
| -4- The chief problem to be overcome when feeding direct to the carburetter, is the sudden pressure fluctuations characteristic of most direct acting or piston pumps of which the Martin is a slow speed type. The maximum pressure regulation provided by the spring operated discharge makes this pump automatic in so far as the variations in capacity require but it does not necessarily cover the question of sudden fluctuations, generally due to hammer on the closing of the discharge valve. To check these accurately an indicator was placed in the discharge line (it was found that an ordinary Bourdon gauge jumped) and an air vessel was also connected and tests made both with and without this vessel. Readings were taken at 1200 and 650 r.p.m. The cards show that maximum fluctuations were experienced at maximum flow, while at zero flow there were no fluctuations. It is of interest to note that at no time did the fluctuations rise materially above the pressure at zero flow. The effect of the air vessel did not show up appreciably, on the indicator, but the gauge, which was also used, showed a slight increase of fluctuations when the air vessel was disconnected. The carburetter, which was tested up to 4½ lbs without leakage, showed no signs of flooding during these tests except when the outlet was closed quickly, when the sudden arresting of flow caused a momentary discharge from the jet. Three rates of flow were chosen for this test, in order to approximate different engine conditions, viz., Zero (engine shut off) 90-120 pts/hr (engine running full out or thereabouts) and a flow approximating the maximum delivery of the pump at the height of discharge under which operating. Discharge heads were 0'4" and 8'8". (e) Tilting of pump. The pump was tilted to an angle of 50° from the vertical and operated at 1200 r.p.m. No difference was noted in the capacity. Owing to the light construction of the valves and their short stroke it is probable that once started the pump would continue to operate in any position. The direction of tilt would not affect valve operation. (f) Hand Operation. The pump was operated by hand at the rate of 60 strokes per minute and gave a flow of 12 pts/min. The stroke when hand operated was 1/4" and, owing to the construction of the cam and yoke, the stroke is the same whatever the position of the cam. This means that under extreme conditions the diaphragm is subject to a compression when at full stroke, of 31/32" or practically 1/16" per diaphragm. The tension of the spring makes the pump rather stiff for hand operation and it would have to be firmly fixed in a convenient position if it is decided to use it in this way. It has the advantage that, if used properly excess pressure cannot be generated. Contd. | ||