fire safety curtain Figure 12. Fusible link. Figure 10. Detail of dashpot system. Figure 13. Detail of Electronic Thermal Link. Figure 11. Detail of hydraulic piston. Modern fire safety curtain systems leave the overbalance weight on the curtain for its full travel and use a more reliable method of controlling the fire curtain's descent called a hydraulic dashpot. This device (figures 10 and 11) is like an oversized shock absorber. Attached to the piston is a rod which sticks out through the top of the cylinder. On top of the rod is a sheave with a cable. The cable pulls the piston upwards and oil is forced from the top of the cylinder through a pipe containing a partially closed valve and the oil reenters the cylinder at the bottom below the piston. The partially closed valve is a restriction impeding the flow of oil from the top of the cylinder to the bottom. This valve controls how fast the cable can move the piston, thus slowing the rate of descent of the fire curtain. Dashpots typically have a five-foot stroke which effectively slows the descent of the curtain for the last ten feet of travel. There are two ways to rig dashpots. The cable passing TD & T F A L L 2 0 0 5 25