10 SURFACE MACHINERY AND METHODS FOR OIL-WELL PUMPING.
B. t. u. per square foot of exposed surface per hour per degree of
difference in temperature between the contained steam and the exter-
nal air. If a sufficient thickness of the better types of insulating
material is used this radiation may be reduced to less than 1 B. t. u.
Covering the drums of return tubular boilers with one row of brick
on edge and a thin layer of cement on top is a common practice; it
helps to save heat, but probably does not reduce the loss to less than
2 B. t. u. per square foot.
A better practice has been to cover the drum with a thin layer of
magnesia and then a layer of cement. However, the expansion and
contraction of the large metal surface of the boiler crack the cement.
A good modern practice is to cover drumheads with magnesia block
or plastic magnesia held in place with netting and covered with
painted canvas. Asbestos and magnesia insulating cements are well
suited to cover irregular boiler surfaces and fittings where either in-
sulating blocks or sectional covering can not be placed.
In most of the locomotive-type boilers seen in oil fields no provi-
sion is made for preventing the loss of heat by radiation from the
boiler surface. On cold windy days many boilers that ordinarily
give the desired steam pressure and capacity are unable to supply
the necessary steam. It is surprising how much fuel can be saved by
a well-closed boiler house when the weather is cold or windy.
Most of the locomotive and return tubular boilers used in oil fields
have individual sheet-iron smokestacks, 15 to 30 feet long, which
are held in place by guy wires. The height of stack necessary de-
pends on local conditions and whether or not mechanical draft is
A central power plant generally has one common chimney of ma-
sonry, reinforced concrete, or brick-lined steel anchored to a founda-
tion, or else a steel stack carried on a foundation or structural
support and held in place by guy wires.
As a rule, steel stacks are not so long lived as masonry; they rust
out under hard service and require more care. However, they are
much cheaper and can be readily moved from place to place. A steel
stack radiates more heat than a brick or concrete chimney. This
loss of heat means loss of draft and less boiler efficiency. Too high
a stack or too strong a draft without proper regulation of the air
supply will greatly reduce the efficiency of the plant, especially when
the load varies.
An oil or gas burner in itself tends to increase draft, which is the
reason for the good draft conditions in oil-field boilers with sheet-
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 May 22, 2013.