SPRINKLER SYSTEMS - 7
On new lawns there is, of course, no turf in the way. The underground irrigation system should be installed before the lawn is seeded. You will find that the irrigation system will be a great help in obtaining good germination of grass seed, and that it will function as insurance against the killing of the young grass by dry weather before it has established a good root system. Digging the trenches for the fife. Even in regions where the winters are extremely cold it is not necessary to bury the pipes of lawn-sprinkling systems deeply, because they are always emptied of water before the ground freezes. However, the lines cannot be installed just under the surface of the ground because streaks may consequently develop in the grass immediately over the pipes, owing to inadequacies of moisture and plant food in the very shallow soil. Depths of 8 to 12 in. are preferred for the pipe lines because these , are not deep enough to require excessive labor and yet are deep enough to avoid any visible effect on the grass above the pipe. The general principles of ditching are discussed in Sec. 376. In making trenches for the lawn sprinkling system, the width of the trench is determined not by the width of the pipe to be installed, but by the width of the spade; therefore, buy or somehow obtain a narrow spade, even though you are not going to have to dig more than one hundred feet of trench. Insert the spade to approximately the same depth every time you push it into the ground so as to make the bottom of the trench as even as possible. It is much better to lay the pipe lines on undis- turbed soil than on soil which must be put back to fill hollows which were dug out unnecessarily. Pile the soil evenly to one side of the trench in such a way that it can easly be raked into the trench after the system is completed. Large stones and ledges of bedrock will create difficult problems in the installation of any underground piping. If the soil of your lawn contains such impediments, it is advisable to dig the trenches to the minimum depth which has been suggested rather than to the maximum. If ledges and large stones are encountered even at a depth of 8 in., there is no short cut around them. It will be necessary to dig the stones out and fill the holes by tamping soil. Ledges will have to be cut through. Pipe can be safely bent over stones and ledges only in regions where the ground does not freeze in the winter. In other regions the "humps" produced by bending the pipe would interfere with draining it in the fall. As we have already mentioned, in fine-grained soils, especially the firmer clays, it is necessary to construct small pits underneath each drainage valve to facilitate seasonal draining of the system. The positions of these pits will be indicated by the stakes you have set to locate the valve boxes. When you come to these points, merely enlarge and deepen the trench sufficiently so that there will be adequate pits underneath the drain valves. Before the pipe is laid, these pits should be filled with coarse gravel or with small stones averaging about one inch in diameter, either of which mate- rials should be firmly tamped in place and brought up to the level of the trench bottom. Grading of the underground pipe lines so that they can be completely drained is absolutely essential in all climates with freezing winters. Not much of a slope is required; in fact 1 in. in 20 ft. is quite adequate if the trench bottoms are made without humps or sags, so that the pipe lines rest evenly. Trenches which carry sewer lines or lines of drain tile can be sloped only in one direction; but there is no such restriction on the lines of a lawn-sprinkling system since drain valves may be placed wherever they are needed. It is desirable, however, to use only as many drain valves as are absolutely required. Not only does each one add to the cost of the system, but, if they are numerous, some may be overloaded when the system is drained. In a small system, rectangular in shape, all the lines are usually sloped so that they can be drained back to a single point, usually adjacent to, or integral with, the supply valve. This is the simplest and the most convenient arrangement for drainage. However, the shape and grading of many lawns make this ideal solution impractical. In such lawns the slopes of the pipe lines in the system must be planned and carried out so that opening of all the drain valves, wherever they are located, will empty all of them. line of pipe in which the high point is somewhere between the two ends must be drained toward both ends; whereas a line in which there is a point between the two ends which is lower then either end can be completely drained only through the lowest point. These are the principles which must be kept in mind in planning the location of the drain valves whether the grading of the system is simple or complex.
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