Author(s): Vicente S. Fuertes; Pedro L. Iglesias; P. Amparo Lopez; Daniel Mora
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Abstract: The presence of air in water supply systems is, in many cases, unavoidable. The presence of air in the pipes may be explained by various reasons and causes a large number of problems, which can even become catastrophic for installations. A good solution to avoiding these problems is the use of air valves. Most manufacturers provide the graphic behaviour of their air valves by means of curves representing head losses vs. air flow through the valve. Proper sizing of air valves is essential for effective, efficient, and safe air control. Improper sizing of an air valve could lead to the rapid expulsion of air, which might result in excessive pressure surges. There is no accepted, standardized method to determine air release flow requirements. Large orifice air valves must be carefully sized in order to avoid problems in functioning. In effect, it is necessary that air valves exhibit great intake capacity to laminate low pressures, but at the same time, controlled venting capacity to avoid unwanted water hammer effects. As the high velocity water flow reaches the air valve float and slams it shut, a very high local up-surge may occur, reflecting and propagating into the pipe. As a consequence, air/vacuum valves should allow air out of the pipe, but at limited speed to prevent water from slamming when air is eventually released, which would cause unacceptable shocks or water hammer conditions. It is important to design air release valves to avoid excessive pressure surges.
Year: 2009