Automatic drain for compressed air systems

In combination with a compressed air system and the like having a liquid collecting sump under the elevated pressure of the air system, a valve for draining the sump without substantial loss of air comprising a valve body having an inlet connected to receive liquid from the sump under said elevated air pressure and an outlet for said liquid to a lower pressure, a valve member rotatable in the body for blocking flow through the body in all angular positions of the member, said body having cup means presented to the inlet in one angular position of the member to receive liquid from the inlet and presented to the outlet in another angular position of the member to empty the cup means, and means for continuously rotating the valve member.