TESTS 



INTERNAL PRESSURE AND PERCOLATION TESTS 



The resistance to internal pressure has long been a standard test 

 for sewer pipe, but the test has not been applied to irrigation pipe 

 or drain tile to any extent. Comparatively little irrigation pipe has 

 been laid where it could be subjected to high pressure heads, and 

 failures of drain tile are due invariably to external loads. 



The test is madf by sealing the ends of the pipe in some way and 

 forcing the water into the pipe by means of a small pump, or admit- 

 ting the water from a water pipe line. Usually a single joint of pipe 

 is taken, but in some instances several joints of pipe have been 

 cemented together and tested as a unit. An entire pipe line, or sec- 

 tions of a line, can be tested after the laying and backfilling are 

 completed, but, of course, no effort is made to test such lines to 

 destruction. 



The equipment used for making the tests here reported is shown 

 in Fig. 24. The equipment is at the Tucson city pumping plant. 

 There is a heavy frame with a platform at the bottom and an in- 

 verted jackscrew at the top. On the platform is a heavy circular 

 iron plate, through the center of which is connected a -)4-inch pipe. 

 Gaskets of rubber three-sixteenths of an inch thick were used at 

 both top and bottom. On the upper gasket a •_>'4-inch circular cast 

 iron plate and a circular wooden cover 3 inches thick were placed, 

 and over the latter a short block of wood 4 inches by 4 inches. The 

 upper cover carried a small pipe outlet, to permit the escape of air. 

 The maximum water pressure obtainable was about 50 pounds per 

 square inch. A pressure gauge was attached so that it measured 

 the pressure at the midheight of the pipe. In order to control the 

 pressure readily and to apply it slowly without shock, a bleeder 

 valve was provided as shown in the lower right hand corner of 

 Fig. 24. This equipment had been used previously to test clay 

 sewer pipe. 



Usually, when the tests to be made are few in number, the pipe 

 is laid on its side and two wooden or iron bulkheads are fastened 

 on with one or several longitudinal rods running through the tile 

 or just outside it. Nuts on the ends of these rods are tightened 

 sufficiently to prevent leakage around the gaskets. The vertical 

 frame and jackscrew have the advantage of convenience and speed. 



Internal pressure tests are attended by considerable difficulty. 



