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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 fuel pipe placement and its effect on vehicle performance and vapour lock.

Identifier  ExFiles\Box 149\4\  scan0304
Date  31th May 1937 guessed
  
The pipe was inside the frame and temp. taken behind X member.

[Table 1]
Columns: AIR, U.B., Frame Inside out. Pipe, Tank.
Max. M.P.H. Columns: All (III gear), double (III gear), single pumps.
Row 1: AIR 17, U.B. 43, Frame... 32 28, Tank 17°C. | M.P.H: All 78, double 78, single 76
Row 2: AIR 18, U.B. 50, Frame... 42 30, Tank 28° | M.P.H: All 78, double 78, single 60 top
Row 3: AIR 18, U.B. 50, Frame... 46 31, Tank 32 | M.P.H: All 70, double 70, single 55
Row 4: AIR 18, U.B. 50, Frame... 44 32, Tank 36 | M.P.H: All 65, double 65, single 40
Row 5: AIR 21, U.B. 53, Frame... 43 34, Tank 38 | M.P.H: All 52, double 52

The pipe to the pump was outside the frame.

[Table 2]
Columns: AIR, U.B., Frame Inside out pipe, Tank.
Max. M.P.H. Columns: All, Double, Single Pumps.
Row 1: AIR 17, U.B. 50, Frame... 42 33, Tank 26 | M.P.H: All Max., Double Max., Single 70
Row 2: AIR 17, U.B. 52, Frame... 46 34, Tank 36 | M.P.H: All ", Double ", Single 64
Row 3: AIR 16, U.B. 53, Frame... 46 33, Tank 44 | M.P.H: All ", Double ", Single 56

In this case the tank temperatures were high owing to a X wing from the N.S. of the car, inspite of the lower air temperature, but there is a noticeable gain in the maximum M.P.H. using a single pump with the pipe outside the frame.

When ever the maximum speed was reduced either using the double or all three pumps made no improvement.

With the present arrangement of pumps on the dash we are open to vapour trouble but it is difficult to predict with certainty how serious this may become as it is dependent on several factors.

(1) Type of fuel used.
(2) Tank temperature reached in ordinary running.
(3) The under bonnet temperature.

Apart from whether this will be a serious complaint is not the pumps in this position have to pump all the vapour formed in the system and with high temperature and only moderate engine demand they are working to nearly maximum capacity with the attendant wear on points and diaphragms and noise.
  
  


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