SPRINKLER SYSTEMS - 4
Sprinkling heads
A good deal of experimentation and experience have gone into the design of sprinkling heads for lawn irrigation; and the types and makes which are now on the market will usually give satisfactory service over a long time without repair and without maintenance other than occasional cleaning and minor adjustments. Some of the heads now available are designed to remain flush with the turf at all times. Others are so built that the part of the head which distributes the water automatically rises a few inches above the turf when the water is turned on, and drops back again to the level of the turf when the water is turned off. This latter type is known as a pop-up head. Pop-up heads are somewhat more ex- pensive than stationary heads because they have more mechanism, but most of them are designed to cover a somewhat larger area. Therefore, although pop-ups cost more, there may be some saving gained in the number of heads required and also in the amount of pipe required for the supply lines. It is now known that it is better for most grasses not to cut them too short. Pop-up heads are the more suitable type for long grass because they stand above it while sprinkling; whereas a heavy, long turf around the stationary type of head which is installed flush with the surface of the soil will interfere somewhat with the distribution of the water. On the other hand, pop-up heads are a little more likely to get out of order; and they will not operate satisfactorily on low water pressures. Most heads used in irrigation systems in lawns have a circular spray pattern; that is to say, a full head will distribute the water over a circular area. However, there are heads on the market which cover an area of lawn which is approximately square. The advantage claimed for the latter type is that it does not waste water since there is no overlapping of areas sprayed by adjacent heads. The spray pattern of a system using circular heads is shown in As the diagram shows there is a certain amount of overlapping which can- not be avoided, since the alternative would be gaps between the spray patterns where the grass would not get watered at all, or watered very lightly. The spray pattern of a system using square heads VARIES. It is claimed that the amount of water saving with the square heads is about 35 per cent. Undoubtedly the water saving is considerable and also important where the water is metered. However, lawn sprinkling systems are not operated in closed rooms. They are operated out of doors where there is, in most regions, enough breeze most of the time to interfere considerably with the spray pattern produced by any type of sprinkling head. It is doubtful therefore, whether anyone can select a special type of head and be certain that his saving of water will be a certain specific percentage. A good policy in selecting heads is to use a type and make which your neighbors have found satisfactory. If you want to experiment with other and perhaps novel types, buy only one or two of them at first and try them out. Such a procedure does not give the inventor or manufacturer who is promoting the device the best of opportunities, but it does place upon him the burden of proving that his particular variety of head is superior. Except where water is unusually high priced, durability and freedom from clogging are probably more important qualities than a theoretical saving of water. This statement should not be construed as a warning against using the type of head which produces the square spray pattern. It is merely intended to point out that one should look for several qualities, only one of which is economy in the use of water.
Spray pattern of square heads
Although most heads used in installations are the full-area type, that is to say, they spray a full circle or a full square, it is necessary to use modified heads in most systems. For example, if full-area heads were used along the curving walk in the walk, as well as the adjacent lawn, would be sprinkled whenever the heads were in operation. However, by using, at appropriate points, heads which are built so that they spray only one-quarter or one-half the normal area, the grass receives its full quota of water right up to the edge of the walk and the walk is not wet. These modified heads are available in styles that will produce one-half, one-quarter, and three-quarter patterns. The shape of many lawns makes it impossible to lay out an irrigation system so that standard full-area heads can be used at every point. We have just explained how boundaries are taken care of, but there is still one other variation necessary. Say that the normal coverage of the heads obtainable is a 12-ft. circle or a 12-ft. square, but the lawn includes a strip of grass which is only 8 ft. wide. This problem must be handled by using an adjustable head. Adjustable heads are offered by practically all manufacturers. In most makes the adjustment is very simple and consists of something like a brass screw which can be turned in with an ordinary screwdriver. As it is screwed in, the screw restricts the size of the waterway within the head and thereby reduces the size of the spray area. Unless the water used is exceptionally clean, adjustable heads, especially after the waterway has been reduced by turning down the screw, are subject to clogging. They do not clog often unless the conditions are very bad, but any clogging is somewhat of a nuisance. Because of this difficulty, they should be used only where necessary. A different type of nozzle or head which is often needed in small systems as well as large is the shrubbery head. It is installed on a riser pipe which extends above the ground about to the top of the shrubbery. Usually the length is adjusted so that the shrubbery just conceals the sprinkling head, but does not obstruct the flow of water. Shrubbery heads are necessary where there are large clumps of plantings which must be watered, or where the placing of a clump makes it impossible to water an adjacent strip of grass with a standard head. If it is properly installed, the shrubbery head can give adequate irrigation to both shrubbery and adjacent lawn in difficult areas of many shapes and sizes.
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