Air Valve Slam

Air valves (Vacuum Breakers) provide a necessary function in some pipelines and plant. This can be to release vacuum in pump risers, to expel gases or to enable rapid priming 

Air and gases entrained in the pumps and within the process can accumulate unless air valves are installed. These small air bubbles coalesce into pockets and that then causes higher pressure drops which cause lower flows.

In addition pockets of air can amplify surge pressures by considerable amounts (102-150% are typical).

So it has become good practice to carefully choose the gradients of the pipes and to install air valves at correctly chosen locations so that air can be safely removed. This minimises the risk of collecting air/gases and hence the associated reduced capacity and  amplified surge pressures.

 

But the size and location of air valves needs to be selected carefully to deliver the required results and to avoid over-design.

For example, over-sized air valves can cause high surge pressures that we call ‘Air Valve Slam’ that have been shown to damage the air valves making them ineffective in the future and also to cause damage to the adjoining pipes.