Recent research has shown that air pockets cause extensive damage and hindrance.
They reduce flow capacity and cause energy and head loss.
They promote corrosion. Hydrogen sulphide is a well-known cause of corrosion in wastewater pipelines. Most of the studies on the topic acknowledge the contribution of air pockets to the problem, but are silent on preventing them.
They can trigger and/or enhance pressure surges. In the past it was accepted that air pockets dampen surges. But, recent research has shown, that in certain cases, air pockets can induce or exacerbate surges.
These surges can cause significant damage, especially if the pipe has been weakened by corrosion. This can cause an expensive disaster.
Sometimes engineers are reluctant to specify air valves for wastewater applications but modern air valves have overcome the reasons for avoiding them. They’re reliable and efficient.
Air valves are a very cost-effective way of preventing air pockets accumulating in wastewater pipes.
Naftali Zloczower of A.R.I. Flow Control Accessories wrote an in-depth paper on the subject. It’s available here.