35 2 FARM MOTORS 



pander to a steam-tight joint. The Prosser and Dudgeon 

 expanders are the two types in common use. 



The Prosser makes a shoulder on the inside of the 

 sheet as well as on the outside, but permits the tubes to 

 touch only at the outer edges (Fig. 240), while the 

 Dudgeon expander enlarges the end of the tube and 

 causes it to fit the full thickness of the sheet (Fig. 241). 

 Owing to the construction of this type of expander, it is 

 preferable for repair work. 



483. Manholes and handholes. These are openings in 

 the boiler to pe/mit of cleaning and examining. The 

 use of a manhole is confined to stationary boilers and is 

 generally placed near the top in an opening about n X 15 

 inches. Handholes are generally in the water legs or 

 near the bottom of the boiler. Their accustomed size is 

 about 3X5 inches. The plate used to cover these holes 

 is held in place by a bolt passing through a yoke. To 

 secure a tight joint, a ^-inch gasket is placed between 

 the plate and the boiler shell of the handholes. The 

 same style of gasket is used for the manholes, but it 

 should be about % inch thick. 



484. Safety valves and steam gauges. The safety valve 

 should be placed in a pipe by itself, and this pipe should 

 be inspected often for stoppages, etc. The safety valve 

 and steam gauge should be set for the same pressures; 

 that is, if the valve blows off at no pounds, the gauge 

 should not read 100 or 120. In case this should happen, 

 do not set the valve to blow off according to the gauge 

 until the gauge has been tested by some gauge known to 

 be correct. During freezing weather the gauge should be 

 taken off every night and put where it will not freeze. 

 Every morning before starting up the safety valve should 

 be tried to see that it neither leaks nor sticks. 



485. Water glass. There is a cock at each end of the 



