An Automatic drain is a 2/2 valve which closes when the system is pressurized

The Drain opens when liquid accumulates and causes the float to rise, and on depressurization

Automatic Drains are good for when the filter location in the application makes access for servicing difficult, or for when equipment is in continual use and disruption for draining is not a preferred option

Applications where large quantities of water can accumulate over a short period of time justify the installation of an Auto-drain