578 HYDRAULICS AND ITS APPLICATIONS 



EXAMPLE. 



Hydraulic engine, 12 inches diameter, 12 inches stroke. 

 p = 750 Ibs. per square inch, mean piston velocity 3 feet per second, 

 length of ports 2 feet ; / = '01. Here L 1 ; Z) = 1 ; Z = 2 : 



Wenowhave * = | X ( 1 X 



Neglecting the --in the last factor, we get d 6 *0157 as a first 



approximation, from which d = '50 feet. 



Fanfnf 1 _1 __ 



d 



Substituting this value of d in the factor 1 + -r, we now get as a 



second approximation 



d 6 =.-0157 X 1-2= '0189, 

 giving d = '515 foot = 6 T 3 g inches. 



If this value were adopted for d in the last factor of the above 

 equation, and a solution obtained as before, a still closer approximation 

 to the true value would be obtained. Generally, however, a second 

 approximation gives results which are sufficiently close for any practical 

 purpose. 



If this method be applied to the design of the Brotherhood engine 



(Fig. 265), having a 5J-inch cylinder with 4-inch stroke, working at 



forty-seven revolutions per minute (v (mon) = *52 feet per second) and 



having a port length of 18 inches, taking /= '010 we have : 



, 6 _ 2'62 X ("52) a X 7 6 / '075 \ 



~ 1-5 X 3 X 16 6 X 750 { d J 



From which we finally get d = '116 foot = 1*39 inches. 



The area of this corresponds to that of a rectangular port If inch( 

 wide by f inch deep, as compared with the actual dimensioi 

 If inches X f inch. 



This investigation shows the importance of having as far as possil 

 separate inlet and outlet ports for these engines, or, where using a singl 

 port, of designing this so as to remain full until readmission takes ph 

 Where this design is carried out the port area may be arranged to 

 give a mean velocity of flow of from 2'5 to 3*5 feet per second. In the 

 alternative case a smaller port area will in general give better results, the 

 velocity being increased up to a maximum of about 8 feet per second. 



