VENTILATING 



129 



together by special couplings so that the 

 shaft will be perfectly rigid. A method 

 sometimes used is to screw the lengths of 

 pipe into an ordinary sleeve coupling as 

 far as they will go; drill a hole through each 

 end of the coupling and pipe, and rivet all 

 together with tight-fitting rivets. This 

 method is less satisfactory, however, than 



Fig. 69. Malleable iron shaft couplings 



the use of split malleable iron castings sev- 

 eral forms of which are to be had. These 

 castings are longer and stronger than the 

 usual sleeve coupling and they thus have a 

 firmer grasp on the pipe. 



They usually have pins or lugs cast in 

 the inside which fit into holes drilled in the 

 pipe at the proper positions, and the two 

 parts are clamped tightly in place by means 

 of bolts. A special advantage of this meth- 



