STEAM ENGINES 209 



the links back and forth. When no pass-over is fitted, but the 

 high-pressure engine can have its valve or valves worked by 

 hand, steam can be got into the low-pressure engine by work- 

 ing the high-pressure valve or valves back and forth by hand. 

 If no way exists of getting steam into the low-pressure cylinder 

 while the high-pressure crank is on a dead center, it must be 

 pulled or jacked off. 



If the air and circulating pumps are attached to and operated 

 by the main engine, a vacuum cannot be generated in the 

 condenser until after the main engine has been started. Con- 

 sequently, in this case, there is no vacuum to help start the 

 engine; therefore, if it is tardy or refuses to start, it will be 

 necessary to resort to the jacking gear and jack the engine 

 into a position from which it will start. A vacuum having 

 been generated in the condenser beforehand, the pressure in 

 the receiver acting on the low-pressure piston causes the engine 

 to start promptly, even though the high-pressure crank may 

 be on its center. 



Stopping Compound Slide-Valve Engine. Compound slide- 

 valve engines, whether condensing or non-condensing, are 

 stopped by closing the throttle, and, if a reversing engine, throw- 

 ing the valve gear into mid-position. If the stop is a permanent 

 one, the usual practice of draining the engine, steam chests, and 

 receiver, closing stop- valves, stopping the oil feed, etc. should be 

 followed. If the engine is intended to run in both directions in 

 answer to signals, as in the cases of hoisting, rolling-mill, and 

 marine engines, the operator, after stopping the engine to signal, 

 should immediately open the throttle very slightly, in order to 

 keep the engine warm, and stand by for the next signal. If 

 the engine is fitted with an independent or adjustable cut-off 

 gear, it should be thrown off, that is, set for the greatest 

 cut-off, for the reason that the engine may have stopped in a 

 position in which the cut-off valves in their early cut-off posi- 

 tions would permit little or no steam to enter the cylinders, 

 in which case the engine will not start promptly, and perhaps 

 nut at all. While waiting for the signal, the cylinder drain 

 valves should be opened and any water that may be in the 

 cylinders should be blown out. When dry steam blows through 

 the drains, the cylinders are clear of water. 



