An end effector is disclosed for an articulated arm. The end effector includes a valve assembly including a plurality of supply channels, each supply channel including a supply conduit, a pressure sensor in fluid communication with the supply conduit, and a supply conduit plug. The supply conduit is in fluid communication with a vacuum source. During use, each supply conduit is either at vacuum such that the pressure within the supply conduit is substantially at a vacuum pressure, or is at a pressure that is substantially higher than vacuum pressure because the supply conduit plug has moved to block a portion of the supply conduit. The pressure sensor of each supply conduit provides a pressure sensor signal responsive to whether the pressure in the conduit is either substantially at vacuum or is at a pressure that is substantially higher than vacuum.