Anti-Vacuum Valves for Coffee Machines

What is an Anti-Vacuum valve?

An Anti-Vacuum valve is essentially a one way valve which once steam pressure starts to build in the boiler, it pushes the valve up and shuts the valve to allow the boiler to pressurise in order to build steam pressure for milk frothing. They are usually 1/4" male thread and all coffee machines have these valves, the difference is the thread size.