Record of Recent Construction, No. 13. Page 10
BALDWIN LOCOMOTIVE WORKS
It is often convenient to ascertain the amount of tractive power developed by a certain size cylinder with given
diameter of driving wheel, irrespective of the boiler pressure. In other words, to determine the tractive power per
pound of mean effective pressure. Plate N o . 4 gives this calculation by graphic curve.
T h e figures at the top of the chart indicate the diameter of the driving wheels, and those in the left hand
margin indicate the tractive power per pound of mean effective pressure. The curves represent the size of cylinders.
The diameter of drivinc wheels and size of cylinders having been determined, the intersection of these two lines
followed to the left hand margin will give the tractive power per pound of mean effective pressure required. This
amount multiplied by the total mean effective pressure in pounds will give the total tractive power. The formula from
which these curves are deduced is as follows :
As X S
— = T '
in which D
A equals diameter of cylinder in inches. D equals diameter of driving wheels in inches.
S equals length of stroke in inches. T' equals tractive power per pound of M . E. P.
The total tractive power developed by the locomotive may be ascertained by a process similar to that before
described, but in which the boiler pressure is taken into consideration, as shown in the following plates.
The tractive power is based entirely on the capacity of the cylinders, and it is assumed that the weight on
driving wheels will be sufficient to develop a corresponding adhesion.
The mean effective pressure is taken at 85 per cent, of the boiler pressure, and the formula on which the
calculation is based is as follows :
A 2 X S X P
= T
in which 1)
A equals the diameter of cylinder in inches. P equals the mean effective pressure in pounds.
S equals the stroke in inches. T equals the tractive power.
I) equals the diameter of driving wheels in inches.