To understand how an umbrella opens and closes, it is necessary to understand its construction. Any umbrella, from huge patio versions to the little emergency umbrellas small enough to fit into a purse, work on the same principle. Waterproof material is stretched over a circular fan of springy metal ribs that attach at the top of the umbrella shaft. These, in turn, are supported by metal stretchers attached to a runner that slides up and down the central shaft. Without the stretchers, the umbrella would not work.
While each part of the umbrella is necessary for its operation, the runner is the part that opens and closes it. When the runner is all the way down, the stretchers are folded flat against the shaft and the umbrella is "closed," with the waterproof material and the ribs wrapped around the shaft. To open the umbrella, the user slides the runner all the way to the top. The stretchers extend, raising the ribs to which they are attached and spreading the material tight over the ribs.
A flat spring toward the bottom of the shaft, and another just below the point where the stretchers are fully extended, lock the umbrella at the open or closed position. The runner slides upward over the extended top spring, which retracts into the shaft out of the way until the runner has passed over it, at which time it springs back out, preventing the runner from sliding back down the shaft. Now the umbrella is locked "open." To close it, the user must manually depress the top spring to allow the runner to slide back down. The bottom spring now comes into play. The runner passes over it to halt just above the umbrella's handle. The spring opens and locks the runner, keeping the umbrella neatly closed.