92 SCIENCE OF SUCCESSFUL THRESHING. 



use an expander. The expander requires considerable care 

 and some experience to use, and in the hands of an inexper- 

 ienced or careless workman, may cause great damage to the 

 boiler by distorting the flue sheet, or rolling the tubes thin 

 and worthless. In using the roller expander, place the flange 

 against the tube sheet and drive the pin in with a few light 

 blows. Then turn it back and forth with a wrench until it 

 loosens. Drive the pin in again, and repeat the operation 

 several times. The roller expander may be used when there 

 is water in the boiler. If a spring or plug expander be used, 

 be sure that it is the right size, and is made to fit the thick- 

 ness of the flue sheet in your boiler. This is very important. 

 To use the spring expander, place it within the tube with 

 the shoulder well up against the tube sheet. Drive in the 

 taper pin with a few light blows and then jar it out by 

 striking it on the side. Repeat several times, turning the 

 expander a little each time, until it has made a complete 

 revolution. The spring expander cannot be used when there 

 is water in the boiler, as the jar of the hammer-blows will 

 be transmitted to the other tubes and loosen them. Use 

 plenty of oil on either style of expander, and carefully clean 

 the end of the tube of soot and scale before inserting the 

 tool. Care must be taken, in expanding the tubes, not to 

 expand them so hard as to stretch or enlarge the hole in the 

 tube sheet, and thereby loosen the adjoining tubes. When 

 all of the leaky tubes have been expanded, they must be 

 beaded down against the sheet with the beading tool. 



