Reducing Cavitation in Valves

Critical cavitation indices are presented for a 12-in. ball and a 12-in. butterfly valve installed in a closed conduit with an enlarged section downstream. Tests were conducted under normal operating conditions and with air (atmospheric and pressurized) and water being injected to control cavitation. Injecting a small amount of air into the low pressure region is a very satisfactory method of controlling cavitation, whereas using water is not. The most critical factor in successful use of air is placing the injection port such that it admits the air as close as practicable to the high intensity shear region between the jet and the separation zone. If the port is properly placed, atmospheric air is satisfactory for reducing cavitation. For valves where it is not possible or practical to locate the injection port in the optimum location, pressurized air can be used effectively to reduce cavitation.