Figure 5 Figure 6 plumbed line from the facility's compressor; the control valve on the smoke pocket (2) with its operating lever (3); the valve (4) controlled by a pilot line (5); and the cylinder (6). Pressure is supplied to the extension port (7) of the piston while the retraction port (8) is left open. A regulator on the control valve input has been omitted for clarity. The two valves are shown positioned as they would be when the system is charged and the wall is in playing position. In the event of a fire curtain release, the curtain would trip the operating lever (3) on the control valve (2) causing the control hose (the dashed line in the schematic and the white hose in the photograph) pressure to drop. This would in turn release the pressure on the pilot (5), letting the spring return move the operating valve (4). When the operating valve moves, the pressure is vented from the cylinder back through the valve, and the wall would move with the force provided by the counterweight. Thankfully there was never a need to use the system in an actual fire, but in tests the system reliably moved half a ton of scenery out of the way before the fire curtain lowered past the top of the wall. s p r i n g 2011 theatre design & technology 35