Frequent use is made in garages, machine shops and other places, of a
special device for hoisting heavy machine parts. The apparatus referred
to is known as a chain hoist. These are built to use chain instead of
rope and are designed to operate slowly, but with great mechanical
advantage. Different types embody different design of movements, some
being merely a train of gears attached to a sheave wheel and driven
by a worm gear. Others employ the differential principle in which the
hoisting chain is double, one end running over a small pulley and the
other end running in the opposite direction over a larger pulley on the
same shaft. As the small pulley unwinds one end of the chain slowly,
the other pulley winds up the other end faster--thus raising the lower
end of the chain loop. Chain hoists are made for various capacities,
and can be built to raise the load any desired distance, merely by
supplying chain long enough. A chain-hoist attached to a travelling
crane makes a very satisfactory equipment for a shop where heavy parts
are to be lifted and transferred and should be used wherever there is
enough such work to warrant the greater first cost.
Fig. 113. A Geared-chain-hoist showing a 1-ton hoist manufactured by
the Wright Mfg. Co., of Lisbon, Ohio, using two chains, one for lifting
and the other for operating.
Fig. 114. A Differential Chain hoist using a single continuous
chain running through a pulley at the bottom and over two different
sized wheels fastened on the same shaft at the top. As one unwinds
the other winds up and the difference in diameter causes one to wind
up faster than the other unwinds.
[Illustration: _Fig. 113; Fig. 114; Fig. 115_]
Fig. 115. A Chinese hoist or Chinese capstan, in which the differential
principle is used. The illustration shows the possibility of quickly
applying the principle to the hoisting of a well-casing. It has the
merit of being cheap and easy to construct and very efficient in
developing a large mechanical advantage. The necessary materials can
frequently be found around almost any farm or construction camp.
[Illustration: _Fig. 116_]
Fig. 116. A Snatch Block is used frequently in connection with hay
handling equipment on the farm. Hoisting hay from a loaded wagon to the
track located in the peak of the barn, requires much more force than is
required to move the load along the track. From then on, the snatch
block pulls away from the knot causing the load to travel on the
carrier track twice as fast as the team. The object is to utilize the
direct pull of the team while elevating the load and increase the speed
of the load and decrease the distance travelled by the team after the
load has been elevated and is to be transferred.