Effects of Air Valves and Pipework on Water Hammer Pressures

Abstract

Many water hammer studies concentrate on the main pipeline and pump stopping. Important details can be overlooked. The rigidity of pipe walls, coatings, and surrounding fill on water hammer in pipes is evaluated. It is shown that backfill increases rigidity and celerity marginally, but pipe material is a major factor in water hammer pressures. The effect of air is to reduce wave celerity but increased surging can occur with some pipework configurations, particularly if air can be trapped. Pump startup can then result in severe water hammer. The correct selection of air valve size and standpipe used to minimize water hammer is discussed. The problem of air valves slamming shut during discharge is investigated and can be remedied with a nomograph. It is shown that large volume standpipes can reduce water hammer due to air valve slamming by providing an air cushion. Other problems of air release and sizing and positioning of air valves are discussed in order to reduce the problem of water hammer.