43. It is claimed by many that such devices inspire the engineer with a misleading feeling of security; that they are more or less complicated in construction and so need care, and destroy the simplicity of the plant; that they may be the direct cause of accident by introducing new elements of danger; that they add to the cost; and that they are not thoroughly reliable. Again, it is held that the surest prevention of overwinding is obtained by the employment of a sober, reliable, and competent engineer, who is held personally responsible for overwinding accidents; by having a good brake and an engine thoroughly under the control of the engineer; by a reliable method of indicating the position of the cage; by sufficient height to head-sheaves to allow of considerable hoisting over and above that necessary for landing.
SIGNALING
44. Some method must be provided for communicating between the bottom or any level of a shaft and the top landing or the engine room, also between the top landing and the engine room, so that the hoisting engineer may be notified when both the head-man and foot-man are ready for him to hoist. A common method of signaling is by means of a gong, bell, or triangle placed in the engine room and connected by a wire or small wire-rope with the point from which it is desired to signal. Attempts have been made in different localities and by different associations to adopt a standard code of hoisting signals, and while it would be advantageous if this could be done, none of the attempts made have been entirely successful. Although there is no uniform system of signals, one bell generally means stop, two bells lower, three bells hoist, and four bells hoist men.
Fig. 40
45. Hammer-and-Plate Signal.—[Fig. 40] shows a hammer-and-plate signal, the plate being a piece of boiler iron or steel. The hammer is often located beneath the plate instead of above, as shown. Another style of hammer-and-plate is shown in [Fig. 41]. The hammer is made of 2-inch square iron and heavy enough to balance the weight of wire hanging in the shaft and to take the sag out of the horizontal wire connecting the top of the shaft with the lever a. A simple dial turned by a ratchet motion attached to the lever a is sometimes used to show the number of strokes, and thus check the number counted by the engineer. The dial is reset by the engineer as soon as he understands the signal.
Fig. 41
Fig. 42