20 



BULLETIN 906, IT. S. DEPARTMENT OF AGRICULTURE. 



joint after the thimble has been forced halfway down into the lower 

 half of the pipe, as shown in figure 4. The remainder of the joint is 

 then finished. The concrete is expected to slide over this metal strip. 

 Joints made in this manner in the laboratory leaked badly when 

 under pressure where a prepared asphalt compound was used to coat 

 the metal strip. If oil be used, it is probable that the bond would be 

 too strong to allow slipping. 



A simple expansion joint (fig. 5) has been tried out that seems 

 to work well under all conditions. A strip or thimble of copper 

 or lead is welded to make a continuous ring, which is about 4 

 inches wide and the same diameter as the center of the shell of the 

 pipe. This strip is then crimped and cemented into a short section 

 of pipe. When the pipe expands or contracts the crimp in the 

 metal gives. Such joints have been found to be water-tight under 

 125 feet head. 



HETAL RING OILED? 



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Fig. 4. — Expansion joints for very low pressure. 



Expansion joints are made and sold by steel pipe manufacturers 

 that are adapted to the use of steel pipe. Such joints are expensive 

 and are not advisable except under unusual conditions. • Bolted 

 joints fitted with rubber gaskets that are commonly used with 

 riveted steel pipe can be used, and will be found to be much cheaper 

 than the commercial expansion joints. Cast-iron collars that fit 

 over the joint and are packed with oakum and asphalt, represent 

 another type. One engineer has suggested using a short length of 

 light weight corrugated iron pipe to be cemented at intervals in the 

 concrete pipe line. Any expansion joint made with steel or iron is 

 subject to corrosion, however. 



Alkali will sometimes disintegrate concrete drain tile and may 

 attack a porous, dry mixed pipe when used for irrigation. Drain 

 tile is subjected to the most unfavorable conditions. The tile is 

 laid where the alkali salts are continually being drained into it. 

 The joints are not cemented and the tile is often only partly full of 

 water. Drain tile is often made inferior to irrigation pipe, the 

 small sizes being made of sand and cement only, with a deficiency of 



