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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).
The principles and troubleshooting of the AC fuel pressure system.

Identifier  ExFiles\Box 27a\2\  Scan012
Date  12th August 1926 guessed
  
AC SPARK PLUG COMPANY
#607
THE NEW AC FUEL PRESSURE SYSTEM CONTROL.

PRESSURE CONTROL:
Pump pressure is entirely a function of the spring used and the maximum pressure exerted on the carburetor occurs at a time when a minimum of fuel is used; namely, when motor is idling, hence when the pressure is correct with the motor idling, no trouble should be experienced at any other speeds.

CAPACITY OF PUMP:
The capacity of the pump in gallons per hour is a function of the maximum movement of the diaphragm and at high speeds of the weight of the spring used. A spring which will give a pressure of 2 lbs. to 2½ lbs. per square inch at idling will deliver 16 to 18 gallons at high speeds, which is 100% excess fuel for any motor on the market.

COMMERCIAL CARBURETOR:
Most carburetors will work satisfactorily with a 2 lb. pressure.

STANDARD PUMP PRODUCT:
A spring giving 1 lb. per square inch pressure is more than sufficient for 70% of the cars using a fuel feed system but from a manufacturing point of view it is very desirable to maintain a uniform product to cover the whole field and this would require a spring with a pressure slightly higher than 1 lb. per square inch.

CAUSES OF PRESSURE TROUBLES:
The trouble experienced with pressure to date are due to two causes:
1. Manufacturing errors
2. Installation errors

1. Manufacturing errors have been carefully analyzed and perfect control can be maintained:
(a) By using a much longer spring which will give the same capacity in gallons per hours, but the spring itself will be less sensitive to variations of compressibility of 1/16" or less.
(b) By weighing every spring with an allowable limit of plus or minus 3 oz.
(c) By assembling the cover on the pump with the spring fully compressed, thus eliminating any possible stretch of the diaphragm.

(The above conclusions are based on a number of tests which have given very uniform results considering the short sensitive spring used. See accompanying test record).
  
  


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