The bucket type of filling must use a counterweight in order to avoid excessive consumption of power, and more difficult control in handling its loads, because from the nature of the case the bucket type of filling must be of the single-hoist variety and therefore unbalanced.

Various methods of arranging the counter-weight are in use. Very generally a vertical tower is used of somewhat less height than the furnace, in which a weight is raised by the counter-weight rope, when the skip is going down. A system of sheaves is used like an ordinary block and tackle in order to get the required counterweighting effect with a short travel by using a proportionately heavier counterweight, as shown by Fig. 23.

The Brown hoist when designed for a single skip eliminates the problems of reversing the engine and of counterweighting the skip by using a hoisting engine in which the drum is connected to the engine shaft through a friction clutch under the control of the operator instead of the ordinary hoisting engine in which the drum is keyed to its shaft and positively connected to the engine shaft through gears. The engine runs always in one direction and the skip is hoisted by throwing in the clutch. On the return trip the skip is allowed to run back by throwing out the clutch and controlling the drum with a brake.

The better type of engine which can be applied by eliminating the need for reversing makes this system more economical, in spite of its loss of power in hoisting the unbalanced skip, than is the ordinary system with the skips balanced but using the very uneconomical type of reversing engine previously described. The Brown system, however, is open to the objection that it requires some skill on the part of the operator in throwing in and out the clutch and lowering the skip with the drum brake, whereas the counterweighted system can be made entirely automatic as to control, etc., by the use of the slow starting and slow stopping devices previously described.

Pig. 23. Ford-Parks system of bucket filling.

Larry Cars

These are almost always used with skip filling and sometimes also with bucket filling. Their essentials are in general always the same, but the details of their arrangement vary greatly. These essentials are a truck, motive power for the truck; a hopper with means for quick and complete discharge, and scales on the truck supporting the hopper. Frequently also there are means for operating the gates on the bins.

Several of the preceding illustrations of bins have shown scale cars also and from these a good idea of the standard types may be obtained. They may be either of the suspended type with their rails elevated close up under the bottom of the bins, which has the advantage that nothing can fall from the chute or hopper onto the rails; or the rails may rest on ties on the ground as in standard railway track.

Many systems of discharge gates have been used and in general the details of the design of these cars are adapted to the conditions of the individual case and the judgment of its designer.

A modified type of larry is used with the original bucket type of filling in which the buckets are removed from the hook of the hoisting truck and taken directly to the bins to be filled, but in this case the more appropriate name of scale car is used.

These differ from the larry principally in having a platform in which the bucket rests instead of a hopper; while, like the larry, their detailed design is adapted to the conditions of the given case.