Pv* r

Then q = — ^ (cos. co + ^ cos. 2 «) approximately. At the dead

grf It

point for the outstroke q^ = -^(l + f) ^^^ opposes the steam pressure

if J

at the dead point at the end of the stroke q^ = — M — -T j and

assists the steam pressure. The space S, travelled by the piston
when the crank arm has turned through an angle a> is given by

S = r f 1 — COS. <a + — L. sin.* o> ) approximately.
This distance S is best calculated by graphical construction.
INEBTIA OT RKCIPROCATDin PARTR,



The case of - = - is ahown in fig. 1027,
For all Tftluea of S the ordinatca are plotted out.
OuWrole—


a = 0;


Si =


6 Pv».
5 grf'




«> = leo"


9. = -


4 P««

5 ^'


Eitum ttrdke (steam preiMiire acting


n opposite diieaion) —




a = 180°


?i =


4 Pv»

6 ?>/■




» = 360°


9. = -


6 PuV
6^'



INERTIA OF RECIPROCATING PARTS. 401

when fi> = 79' ; j = 0*46 H ; q = 0,

(a = 259" ; s = 054 H ; 5 = 0.
Ex<mfle,—Take an engine where D = 16'', H = 28", n = 100 ;
L = 5r.
Then as in preceding example —

P = 798 lbs. V = 12-2 feet per sec.
gr^ = I X 49-4 = 59-3.
5

q^=i X 49-4 = 39-6.
5

Suppose the steam pressure to be 140 lbs. per square inch at the
beginning of the stroke and to be expanded five times ; the pressure

at the end of the stroke would be "^ — 15 = 16 lbs. per

square inch approximately.
