Surface Machinery and Methods for Oil-Well Pumping Page: 103
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POWER TRANSMITTING MACHINERY.
The seam side of a rubber belt and the trade-mark side of other
fabric belts should be run away from the pulleys. It often happens
that endless belts can only be installed by removing the shafting, to
which the pulleys are attached, from the bearings, and then inserting
the belt and replacing the shafting.
Most manufacturers recommend that an endless or spliced belt
should be so placed on the pulleys that the thin edge of the splice on
the inner side will be the first part to come in contact with the pulley.
Endless belts wear longer and cause less wear of the machinery
and bearings. Much of the jumping and lashing of belts, especially
over small pulleys, is caused by the metal fasteners, which prevent a
smooth contact with the pulley face. With the high speeds and
small pulleys used with motor drive, endless belts are required for
Leather belts are usually made endless at the factory. Fabric
belts are now commonly made endless for pumping oil wells from
a central power or jack plant, especially where an electric motor with
a countershaft is used for drive. Sometimes these belts are made
endless in the field by using a step splice, in which the plies are cut
away and overlapped as shown in Figure 16 at G (p. 102). The plies
are first cemented, then stitched, and sometimes further reinforced
With motor drive a belt can be run moderately slack without much
slippage. With steam engine, and especially with gas engine drive,
a belt must be run tighter, as the pulsations of the engine tend to
make the belt lash and slip. However, belts should not be run too
tight, for this increases wear on the bearings, increases the consump-
tion of lubricating oil, and causes excessive stretch which weakens the
belt until ultimately it breaks. Belts that are too tight can be easily
slackened by reducing the pulley centers or by inserting a piece of
belt. Belts too small for the power requirements or pulleys too small
for the thickness of belt often cause trouble. If it can not carry the
load, a belt will break or the lace or the fasteners will give way.
Normally, a belt should be wide enough to run slack without
slipping. The slack side should be on top. Pulleys should be about
the same size when possible; the smaller pulley should preferably
be the driven pulley. A pulley should be at least an inch wider than
the belt. The slip usually is one-half to 2 per cent, and the driving
power will be decreased by this amount. Shafts and pulleys should
be in perfect alignment. Belts poorly aligned often run off the
pulleys or slip.
In pumping oil wells, belts are run at comparatively low speeds,
but with much difference in the size of pulleys. These conditions are
compensating in that the former increases effective tension and the
latter, from the decreased are of contact on the smaller pulley, which
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George, H. C. Surface Machinery and Methods for Oil-Well Pumping, report, 1925; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc12407/m1/132/: accessed December 15, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.