r hoisting in collieries are usually
direct-acting with a pair of horizontal cylinders coupled directly to
the drum shaft. Steam at high pressure exhausting into the atmosphere is
still commonly used, but the great power required for raising heavy
loads from deep pits at high speeds has brought the question of fuel
economy into prominence, and more economical types of the two-cylinder
tandem compound class with high initial steam pressure, superheating and
condensing, have come in to some extent where the amount of work to be
done is sufficient to justify their high initial cost. One of the
earliest examples was erected at Llanbradack in South Wales in 1894, and
they have been somewhat extensively used in Westphalia and the north of
France. In a later example at the Bargold pit of the Powell Duffryn
Steam Coal Company a mixed arrangement is adopted with horizontal
high-pressure and vertical low-pressure cylinders. This engine draws a
net load of 55 tons of coal from a depth of 625 yds. in 45 seconds, the
gross weight of the four trams, cage and chains, and rope, with the
coal, being 20 tons 12 cwt. The work of the winding engine, being
essentially of an intermittent character, can only be done with
condensation when a central condenser keeping a constant vacuum is used,
and even with this the rush of steam during winding may be a cause of
disturbance. This difficulty may be overcome by using Rateau's
arrangement of a low-pressure turbine between the engine and the
condenser. The accumulator, which is similar in principle to the thermal
storage system of Druitt Halpin, is a closed vessel completely filled
with water, which condenses the excess of steam during the winding
period, and becoming superheated maintains the supply to the turbine
when the main engine is standing. The power so developed is generally
utilized in the production of electricity, for which there is an
abundant use about large collieries.

The drum, when round ropes are used, is a plain broad cylinder, with
flanged rims, and cased with soft wood packing, upon which the rope is
coiled; the breadth is made sufficient to take the whole length of the
rope at two laps. One drum is usually fixed to the shaft, while the
other is loose, with a screw link or other means of coupling, in order
to be able to adjust the two ropes to exactly the same length, so that
one cage may be at the surface when the other is at the bottom, without
having to pay out or take up