24 SURFACE MACHINERY AND METHODS FOR OIL-WELL PUMPING.
Engines, either horizontal or vertical, of less than 10-horsepower
rating are used to drive small pumps and to pump shallow wells.
Some vertical types are air cooled and are particularly suited for
small wells, where power is needed only a few hours a day. As they
are air cooled and the cylinder need not be drained in cold weather,
they need little attention.
Gas engines are of two general classes, the two cycle and the four
cycle. In the former, every revolution of the crank shaft pushes the
piston; in the latter, every two revolutions push the piston. Both
types are widely used, but the latter is the more common.
The two-cycle engine has fewer moving parts such as valves and
valve control mechanism, a lighter fly wheel, a more uniform rate of
revolution, a smaller cylinder, and lighter engine to the unit or
power than the four-cycle engine, and simplicity and compactness of
The four-cycle engine has higher efficiency, can be regulated easier
under conditions of varying load, and compression does not depend
upon tightness of any parts except valves and piston rings. The four-
cycle engine is generally provided with a heavier flywheel in order to
bridge the gap between explosions and afford smooth running.
Plate VI shows a typical oil-field gas-engine installation used for
driving a pumping power. The principal engine parts clearly shown
are: a, Engine cylinder; b, inlet chamber; c, engine bed; d, flywheel;
e, valve and governor mechanism; f, Wico magneto; g, hot tube
igniter; h, gas-supply pipe; j, engine-exhaust pipe; k, circulating
water pipe; 1, compressed-air pipe. Other accessories shown as a part
of the installation are: m, Compressor used to start engine; n, air re-
ceived; p, idler; q, power wheel with eccentrics to pump wells; and r,
guard rail at engine. Plate VI shows the engine bolted to timbers
which in turn are bolted to the concrete foundation.
GOVERNING ENGINE SPEED,
The common horizontal gas engine for pumping wells is generally
designed for speeds of 180 to 250 r. p. m. Racing or cutting out
the governor with a by-pass controlled from the derrick gives much
higher speeds for swabbing the well, where this is done. Two gen-
eral types of governors are used, the hit-and-miss and the throttling
The former holds the speed of the engine constant by the missing
of certain explosions on the power stroke when running on light
load. As the load increases the number of explosions increases until
the engine fires regularly. As the load decreases the engine tends to
George, H. C. Surface Machinery and Methods for Oil-Well Pumping. Washington D.C.. UNT Digital Library. http://digital.library.unt.edu/ark:/67531/metadc12407/. Accessed April 23, 2014.