788 



HYDEAULICS AND ITS APPLICATIONS 



Where communication between the two ends of the cylinder is 

 through a spring-loaded valve, in order that the pressure should be 

 approximately constant throughout the stroke it is necessary that the 

 lift of the valve should be small, its weight small, and the resistance 

 offered by the spring as constant as possible over the range of lift of 

 the valve. 



As a liquid for use in recoil cylinders, Castor oil or Eangoon oil is 

 good and keeps the leathers in good condition. A mixture of four parts of 

 glycerine to one of water is also good, as is a mixture of methylated spirits 



FlG. 397. Recoil Cylinder for Canet Gun. 



GG per cent, water 31 per cent., mineral oil 3 per cent., with 25 grains of 

 carbonate of soda per gallon. 



Theory of the Hydraulic Brake. Suppose the piston red to be in 

 compression, 



Let A = effective area of piston in square feet, i.e., area of piston mi HUH 

 that of rod and of connecting orifices, if these are through 

 the piston. 



a = effective area of connecting orifices. 

 L = length of piston travel in feet. 



I length of connecting passages. 



II =. resistance of brake in Ibs. 



p = excess pressure behind piston in Ibs. per square foot. 

 \V = weight of moving body in Ibs. 

 V = velocity of moving body, and of piston if brake is in opera- 



tion. 



v = velocity of fluid through orifices. 

 If the fluid is water we now have 



-_ . 



62-4-20 



m 



m 



