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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 basis of comparison for orifices and the equations for the flow of liquids.

Identifier  ExFiles\Box 36\1\  scan 013
Date  21th February 1917
  
R.R. 25M A (990 T) (S.C. 686 15-2-16) G.{Mr Griffiths - Chief Accountant / Mr Gnapp} 1546.
X.2907.
-1-
RE BASIS OF COMPARISON FOR ORIFICES.
X.2907L/s-FLOW OF LIQUIDS THROUGH ORIFICES.
The flow of a liquid through an orifice is given by the following equation :-
Q = C.A, √2gh.
or = Cv.Cc.A √2gh . P/σ
WHERE Q is the quantity discharged (cubic feet per second).
C is the Coefficient of Discharge.
A is the area of cross dection of the orifice (sq.feet)
g = 32.19 feet per second per second.
h = the head over the orifice (feet).
Cv is the "Coefficient of Velocity".
Cc is the "Coefficient of Contraction".
P is the pressure of the liquid just before reaching the orifice (lbw. per sq. foot).
σ is the density of the liquid (lbs per cubic foot).
The ideal velocity of discharge is √2gh feet per second and the actual is Cv.√2gh ft/sec. where Cv is a coefficient less than unity.
The effective area of the orifice is Cc.A square feet, where Cc is a coefficient less than unity.
Cv x Cc = C. (Coeff. of discharge).
The quantities Cv, Cc, C are not absolute constants for different conditions, but suitable values of these must be selected to suit the particular conditions under consideration.
Contd.
  
  


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