New Developments in the Air Valve Evolution
Air vales have received a lot of attention because they play such a crucial role in pipelines. A brief summary of some of these developments follows:
Standard air valve. Normally produced with a reduced bore to make the body smaller and thus less expensive. These valves are prone to close under high air velocity (pre-closure) if a pipeline is filled too quickly, making them inoperative.
Kinetic air valve. These are equipped with a kinetic shield under the float to prevent closure under high air velocities. The problem with this approach is that the when float closes as the water arrives it results in a high local “slam” often causing damage to the pipe or valve.
Non-slam air valve. Initially developed to protect the air valve and eventually used for surge suppression. Early versions had a separate restricted check valve under the air valve to slow approaching air and water. This became so popular that it was incorporated into the valve by most manufacturers.
A proliferation of these valves appeared on the South African market after the SA patent for the non-slam design ran out.
One of the problems is that these valves cannot reduce the speed of the water column when all the air is already out of the pipeline.
Dynamic air valve. The dynamic air valve is the latest development from the A.R.I. valve works. It solves many water hammer problems that the standard non-slam valves don’t.
The valve reduces velocity (and thus water hammer) by allowing water through the valve for about a second after all the air has been expelled.
This valve has shown significant benefits during independent testing by Mekorot (the Israeli National Water Company).
The results of the testing were published in the Journal of Applied Fluid Transients in an article by Yiftach Brunner of A.R.I. and Sathish Kumar of Fluidhammer Consultancy Services.
The full report is available here.