118 



Bulletin 86 



The ends of the tile are usually somewhat rough and may not lie in 

 a plane, wherefore it is difficult to prevent leakage around the 

 gaskets. Leakage is objectionable for two reasons; first, the over- 

 flowing water from the top gasket wets the outside of the tile and 

 prevents observations on the percolation of water through the tile 

 walls ; second, the leakage is often so great as to reduce the pressure 

 head that can be applied to the pipe. In order to make the gaskets 



Fig. 24. — Testing 16-inch machine-made pipe for resistance to 

 internal pressure, at the Tucson city pumping plant, in 1917. 



tight, the jackscrew is likely to be turned down until an excessive 

 pressure is put upon the test specimen. 



The criticism is made that a heavy longitudinal stress must 

 seriously afifect the resistance to bursting. One specification has 

 forbidden the tests to be made in such a way that the gaskets are 

 held on the pipe ends by longitudinal pressure. Other engineers 

 have asserted that the pipe would burst as the efifect of the heavy 

 compressive stress. As a matter of fact the ends of the pipe must 



