SPRINKLER SYSTEMS - 8
Drain location under special conditions
Cutting and threading the fife. No special technique is required in the cutting and threading of pipe for underground systems other than ordinary care. The pipe threader should be adjusted so that it produces a length of thread on the pipe ends which is just long enough to screw into the fittings, leaving almost no thread exposed. This detail is important in underground systems because the pipe threader removes the protective coating of zinc from the outside of the pipe and leaves the bare steel exposed. The chief difficulty that occurs in the operation of lawn sprinkling sys- tems is due to inadequate pressure at the heads which are most dis- tant from the supply pipe. It can be largely avoided by taking pains to ream out the ends of the pipe after they have been cut and threaded so that there will be no internal spurs to restrict the flow of water. Another precaution which also is aimed at maintaining the full waterway within the pipe is to put thread compound only on the male end of the pipe. If compound is placed on the female end, some of it will inevitably be pushed into the interior of the pipe or fittings, where one of two things will happen to it. Either it will gradually be loosened and carried along in the water to clog the sprinkler heads, or it will harden and form obstacles to the flow of the water. An excess of compound placed on the male threads does not enter the pipe or fittings but backs up along the threads where it adds a little extra protection against corrosion of the joint.
Assembling the pipe
Square-nosed wrenches for holding the brass valve bodies and Stillson wrenches (pipe wrenches) are the tools needed for assembling the cut and threaded pipe and the fittings. The jaws of the Stillson wrench inevitably will cut through the galvanized coating on the exterior of the pipe. It is a good idea to paint these cuts after the joints have been assembled with a paint which contains a lead oxide base. If the joint compound you are using is red in color, it is probably made from a lead compound and should serve very well to paint these scratches. It is more convenient if rather large sections of the underground piping can be assembled above ground and lowered into the trenches after they have been put together. Given the right conditions, rather large blocks of such piping can be put into the trenches in one piece. The requirements are fairly straight trenches and enough men on hand to lower the network of assembled pipes without putting too much strain on the joints. The system can be built inward from the risers to the supply line, or it can be built in reverse, from the supply line outward to the risers. The first-mentioned procedure requires the use of a union where the system is joined to the supply line. If this union will be underground, it is advisable to use the type of union which has a ground joint. The type which uses a washer is not very good underground. Leaks may develop because of the washer drying out during the long periods when the system contains no water. 348. Once the system has been assembled, the joints should be tested. The test can be carried out by this method: The water is turned on and allowed to flow out of the tops of the risers. This carries the air out of the pipes and also removes any loose dirt which is not too heavy to be carried up the risers. After the water has flowed a few minutes, it is turned off and each riser is capped with a standard pipe cap. The water is turned on again and the joints are observed over a period of at least an hour. If a leak can be dis- covered in such a test, it is absolutely necessary to take the joint apart and correct the fault. Very often the leak turns out to be due to the joint not having been screwed together tightly. This is easily remedied. If the leak is due to a defect in the thread either on the pipe or on the fitting, it is necessary to correct it. Unfortunately, there is a tradition that small leaks in new piping systems will correct themselves when rust forms in the joints. Such self-healing does occur occasionally on steam lines in domestic heating systems; but it seldom, if ever, occurs on lines carrying cold water. Instead the tendency is for the leak to grow worse as more water passes through it. The last operation before filling in the trenches is setting of the boxes around the valves. We have already mentioned that these boxes are made of ordinary steel pipe. No threads are required on the pipe. The boxes should be placed over the valves and supported with stones or tamped soil sufficiently so they will not be knocked out of place as the trench is filled. The tops of the boxes should be made fairly level.
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