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steam in the intake manifold. To make fast time coming out of the
hole, it was necessary that the engine be capable of fast accelera-
tion and deceleration. Tо obtain this, the engine was frequently
built without a fly wheel. This results in extreme vibration at
high speed. Because of the above, not only the shaft and
bearings, but the entire engine must be very rugged.
The valve cutoff is a late development. Most of low
pressure industrial steam engines have been designed for a ⅝"
valve cutoff. When steam pressure was increased it was customary to
shorten the cutoff still more in order to take advantage of a
higher steam expansion within the cylinder. This, of course,
decreased the maximum power output but increased the overall
thermal efficiency.
This drilling engine reverses the above idea of efficiency by
being designed for a ⅞" cutoff. High power output and high steam
consumption is the result. It has the old time Stephenson-
type valve linkage familiar to all steam men. Piston-type
valves are used.
Since the Stephenson linkage combines a reversing
mechanism with the ability to shorten the cutoff, some radical
part of the design is cancelled. Because taking advantage of this
increase in steam efficiency would mean lowering the engine's
power, the driller rarely took advantage of it. Speed and more
speed is what he wants in his drawworks. At the present,
steam-powered drilling rigs are a thing of the past. Among the
causes would be the high price of fuel gas. Fuel costs become quite
an item in drilling with steam. Nature of the terrain also enters
into the picture.
Another factor is that at present the bulk of oilwell drilling is
done by contractors. Since a contractor may be in an established
field today and in the sticks on a wildcat tomorrow, he definitely
leans toward internal combustion engines.
On steam-powered drilling rigs the power end of the steam
slush pump is a prime mover. The large duplex slush pumps of

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