FARM MOTORS 



it will be noticed that there is a groove B in the 

 valve such that when the valve starts to open, the 

 steam rushes into it, thus increasing the area of the valve 

 and causing it to open more quickly and remain open 

 longer. To increase the pressure at blow-off, screw down 

 on the pin G ; to lower the pressure, screw up on the pin 

 G. Care must be taken not to tighten the spring down 

 too far, or it will not allow the valve to lift off its seat. 



459. Blower and exhaust nozzle. In all traction en- 

 gines there must be some method of increasing the draft. 

 The most simple method and the one universally used is 

 the blower when the engine is not running, and the ex- 

 haust when it is. 



The blower (Fig. 218) consists of a small pipe with a 



valve which leads from 

 the boiler to the stack. 

 After the pressure has 

 reached 5 or 10 pounds 

 the valve in this pipe is 



FIG. 237 EXHAUST NoIzLE opened and a jet of 



steam is allowed to 

 blow into the stack. The momentum of the steam pro- 

 duces a vacuum and the air rushing through the grates 

 and coal to fill this space increases the rate of combus- 

 tion. When the engine is running the exhaust steam 

 from the heater takes the place of the blower and the lat- 

 ter is closed. Fig. 237 shows an exhaust nozzle, which can 

 be made to give a sharp or sluggish exhaust, as desired. 



460. Blow-off pipe. Wherever there is a chance for 

 sediment of any kind to collect in a boiler there should 

 be some means of cleaning it. This is almost always 

 accomplished by means of a blow-off pipe and valve. In 

 vertical boilers this is located at the lower end of the 

 water leg. In return-flue boilers this is either at the front 



