82 IUKIGATIOJS' FAKMI.NU. 



fountain liead, as otherwise there could be no pressure up- 

 on the pipe and it would stand in relation to delivery on a 

 plane with the ditch or flume. If the line is accommo- 

 dated to the surface and there is any inverted or down- 

 ward bend in the pipe, there should be a valve set at the 

 lowest point to provide for the emptying or draining of 

 the pipe during cold weather, or for repairs. The* pipe 

 may he laid on or near the surface on low supports of 

 such form and material as circumstances may sur^vst. 

 The matter of grade is of little importance, for the water 

 being forceJ will run up hill as well as down, and a pipe 

 may be laid to the natural grade of the surface and de- 

 liver water on a level with the fountain head. 



Pressure of Pipes. For the purpose of consider- 

 ing the pressure we will divide the classes of pipes into 

 three kinds : low pressure pipes, medium pressure pipes 

 and high pressure pipes. By low pressure pipes we mean 

 those which are not required to withstand any greater 

 pressure than that occasioned by the gravity flow of 

 water through them, with the addition of a few feet if 

 necessary. We will designate as medium pressure pipes 

 those which are able to withstand a pressure of fifty 

 pounds to the square inch with safety, and as high pres- 

 sure pipes those which can safely resist a pressure of 120 

 pounds to the square inch. Pipes made of riveted sheet 

 iron or steel No. 16, vitrified clay or cement, are classified 

 as low pressure pipes ; those made of riveted sheet iron or 

 steel No. 14, or of wooden staves banded with wrought 

 iron, are classified as medium pressure pipes ; and those 

 made of sheet iron or steel No. 12, or of cast iron, are clas- 

 sified as high pressure pipes. While these classifications 

 correctly separate the different kinds of pipe into classes 

 on the basis of their ability to resist pressure, still there is 

 also a difference between the various kinds of pipe be- 

 longing to each class. In the low pressure pipes the sheet- 

 iron or steel is the strongest, the vitrified clay the next 



