An anti vacuum valve is fitted to coffee machines to allow air to enter the boiler as it cools, when the machine is switched off.
When the boiler is next switched on the water heats, and as it begins to boil the internal pressure seals the anti vacuum valve.
Symptoms of a faulty valve are that the steam wand produces a small amount steam for the first operation after switching on, and the boiler pressure immediately drops to zero. The machine then works faultlessly until is is next switched on.
Manufactured from stainless steel.
Thread: 1/4" taper.