CHAPTER XVI 



The Hydraulic Engine Brotherhood -Rigg -Theory of Action Losses Port Areas. 



ART. 154. THE HYDRAULIC ENGINE. 



WHERE a supply of high pressure water is available, and where inter- 

 mittent rotary motion at a moderate speed is desired, the reciprocating 

 piston engine has certain advantages, particularly where it is able to work 

 at or near full load, and where the speed variation may be excessive, as 

 occurs, for example, in the working of a capstan. For such work the 

 rotary motor is out of the question, both on account of the necessity 

 for gearing to reduce its necessarily high speed, and of the great 

 reduction in its efficiency under variable speed conditions. The recipro- 

 cating engine, however, having an efficiency which is approximately 

 independent of its speed, and being compact, is particularly well adapted 

 for such work. For small powers, too, where the load is fairly constant, 

 such as for driving ventilating fans, organ bellows, etc., its high 

 efficiency and the absence of noise connected with its use often render 

 it, in the absence of an electric supply, the most suitable motor to 

 use. 



One of the most widely used types of engine is the Brotherhood 

 (Fig. 265), which is designed to work with pressures from 60 Ibs. to 

 1,050 Ibs. per square inch. 



Here three single acting cylinders fitted with trunk pistons are fixed 

 radially at 120 to an external cylindrical casing, the three connecting 

 rods working on a single crank pin. Each cylinder is fitted with a 

 single inlet and outlet port, the opening of this to supply and exhaust 

 being regulated by the rotary valve shown at D in Fig. 265. 



This valve is rotated by the crank shaft, and carries passages con- 

 necting with the pressure supply and the exhaust which are alternately 

 presented before the port of each cylinder in turn. The method of 

 keeping the rotating joints tight against such high pressures is indicated 

 in the sketch. Here A is a leather joint washer, on which the back nut B 

 rotates, the play due to wear on the joint being taken up by the expan- 

 sion of the rubber ring C, which rotates with the valve and back nut. The 



