Environmental Engineering Reference
In-Depth Information
control valve at the programmed time. The valves, positioned sometimes
at individual heads but more often along pipes serving several heads,
control the flow of water from the valve to the last sprinkler head in this
series. Some automatic systems are equipped with soil-moisture sensors
that can override the controller program and prevent the system from
being turned on during or shortly after rain, when soil remains moist.
Modern, fully computerized, automatic control systems analyse essential
weather and soil-moisture data, account for all programmed variations
and modifications, and open selected valves at the best times and for the
proper periods.
In addition to the remote-control valves used in automatic systems,
several other types of valves are used in irrigation systems. A master
valve is used to turn off the entire system, check valves are used to limit
water flow to one direction, antisyphon valves are used to protect do-
mestic water supplies from back-flow when irrigation is completed, drain
valves are used to allow drainage from lines after irrigation, and pres-
sure-regulating valves are used to prevent excessive water pressure.
Larger irrigation systems usually include water pumps (Fig. 7.10).
Two types of pumps are used: booster pumps and system-supply pumps.
Booster pumps raise in-line water pressure without affecting flow rate. In
large irrigation systems, such as on golf courses, booster pumps are used
where water pressure drops considerably as a result of elevation changes
and must be restored. System-supply pumps are used to draw water
from a water source, such as a well, pond or river. A system usually
includes several of them, and each supplies a specific flow rate at a
Fig. 7.10. Water pumps are usually placed in specially constructed buildings that
protect them from weather damage.
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