If now the cage is lifted and the weight thus removed from the jaw a, the spring g pushes the plunger b outwards and allows the oil to run from e back into c.
27. Pneumatic Fans.—A pneumatic fan, shown in section in [Fig. 26], is one in which the shock of the landing is partially relieved by a cushion of compressed air. The fan is keyed at the bottom to the shaft a that rotates it, as in [Fig. 24]. The cylinder b contains the plunger c, which is kept at the top limit of its motion by the spring d. When the cage lands in the jaw e, the plunger descends, compressing the air in the cylinder b. The air escapes slowly through the ¹/₁₆-inch hole f, thus allowing the cage to settle into place with very little shock. These fans should be made of wrought-iron or cast-steel so as not to be easily broken.
Fig. 26
28. Cage Chairs.—In the case of a cage required to stop at a large number of levels, it is expensive to provide fans at each level, and to obviate this a strong steel bar or dog may be used under each corner of the cage, all four bars being connected to a lever on the cage, by means of which they can be thrown out at will so as to rest on supports provided at each level. [Fig. 27] shows Gray’s patent cage chair, which operates on this principle. The sliding bars a are connected by the cross-bars b, which are pivoted at the center and operated by the bar c through the links d. By moving the lever e into the position shown, the bars a are thrown out so as to rest in notches or on wall plates in the shaft. The springs f, through the cross-bars b, force the sliding bars a back under the cage when the lever e is released.
HEAD-FRAMES
29. A head-frame of wood, iron, or steel is built over a shaft or slope mouth to carry the sheaves over which the hoisting ropes are conducted from the mine to the drum of the hoisting engine; it also usually carries the upper portion of the cage guides or, in the case of a slope, the tracks for cars.
Fig. 27