Manufacture of Cement Pipe 



91 



There are six cement pipe plants in California where pipe is 

 made of very wet consistency, so wet that the jacket cannot be re- 

 moved in the ordinary way lest the mortar slump to the ground. 

 Instead of opening the jacket to remove it, the jacket is shaken ofif 

 by quick jerking movements upward. When the jacket comes free, 

 the tile settles over an inch in its length. The tile thus made be- 

 comes strong and is exceedingly impervious. More skill is required 

 than in making dry or semi-wet pipe. 



The hand-made pipe is thicker than machine-made pipe, except 

 in the larger sizes. The usual thickness and weight for the common 

 sizes is given in Table II. The large sizes should be made with 

 thicker walls. It is seen from the table that the 12-inch pipe has 

 wall thickness one-eighth of the pipe diameter, while the 36-inch 

 pipe has w^all only one-twelfth of the diameter. Most of the serious 

 pipe failures have occurred on large pipe lines. This matter is 

 discussed further on page 133. 



TARLE IT. THICKNESS AND WEIGHT PER FOOT OF HAND-MADE PIPE 



Extra strong pipe can be made by using an oversize outside form. 

 One contractor in this way makes 8-inch pipe of two strengths, one 

 having the wall thickness one-eighth inch greater than the other. 

 Sometimes a 14-inch jacket is used with a 12-inch core and the pipe 

 is, therefore, 2^ inches thick. A contractor who makes very wet 

 pipe in this manner states that he guarantees it under 100 feet 

 pressure. 



The working force at Continental for hand-tamped pipe con- 

 sisted of two skilled men and four unskilled laborers, though the lat- 

 ter were not all employed to advantage. The tamper was unusually 

 strong and active, and had had long experience in pipe making and 

 laying. He was able to make from 270 to 300 feet of 16-inch pipe 



