Surface Machinery and Methods for Oil-Well Pumping Page: 87
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Jacks constructed of pipe and castings are common in many oil
fields, and many oil companies make their own. Most of the oil-well
supply companies manufacture them. Pipe jacks are strong and dur-
able. They have the advantage over wooden jacks that they are
less bulky and are not subject to rot.
Plate XXIII, B, shows a jack of the Oklahoma type in operation.
This jack is made of structural steel, pipe, and a bolted timber frame.
The shackle line a is attached by means of a stirrup to a box on the
end of the upper arm of a structural steel jack, b, which is pivoted
by a saddle fastened to the lower arm near its junction with the
upper arm and resting on bearing plates bolted to the wooden frame.
The jack is connected by a pitman, c, to a structural steel beam, d,
which is pivoted at e in the wooden frame. This type of jack is built
in many variations of design and materials. Usually it has a long
beam and is well suited for a long stroke and for service at deep wells.
The Pennsylvania jack, made of timber with wooden frame and
braces, was the first type used in the Appalachian oil fields. Wooden
jacks usually cost less than those made of pipe or structural steel,
but they rot and give trouble from lost motion unless carefully
framed and tightly bolted. Many wooden jacks of the Pennsylvania
type are built with long arms and work well with a long pumping
LENGTH OF STROKE.
With most types of jacks the length of the stroke at the well is
varied by changing the relative lengths of the power and work arms
of the jack, or by varying, with a reference to the fulcrum, the rela-
tive position of the polish rod and shackle-line attachments on the
In many types of jack, the stirrup box to which the stirrup and
shackle line are attached has two or more seats and the length of
stroke can be regulated by changing the seat of the stirrup.
COMPARISON OF TYPES.
The Pennsylvania jack is made and used either with upper or lower
connections. For upper connection, as shown in Figure 8, A (p. 65),
the vertical and power arm of the jack extends up from the saddle
and bearing plate to the shackle-line connection; for lower connection
this arm extends downward as shown in Plate XXIII, A. The
upper connection is not so common, but it is used at many wells in
hilly country on ground lower than the power in order to give a
more direct pull from the power to the jack. It is also used when
there is a particular reason for having the shackle line some distance
above the ground, as where low-lying obstructions would interfere
with the lower connection being made.
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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/m1/116/: accessed September 21, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.