The engine is operated from the derrick by pulling back and forth the 'telegraph cord' (42, Fig. 34), which runs from a wheel attached to the headache-post to the throttle-wheel (40). The reverse-lever is handled in a like manner by moving a Y8 or pipe (34) connecting it with a handle at the derrick. Usually a simple heater is attached to the pulley side of the engine for utilizing the exhaust steam to raise the temperature of the boiler feed water. A barrel-pump, directly connected to the engine crosshead, pumps the water into the boiler. Engines are bought either stripped or complete, the former being without crosshead-pump, beater or extra flywheel balances.
As might be expected where fuel is cheap, little attention is given in the oil fields to steam economy or highly efficient boiler installations, except at the pipe-line pump-stations and the larger central station plants. These frequently have large water-tube boilers, feed water heaters, superheaters, etc., but the boilers scattered about at drilling and pumping wells are more often of simple design and installation.
For shallow drilling in some fields, light portable boilers on wheels are used. With deeper work the common horizontal fire-tube boilers of rated capacities from 30 to 45 horsepower are employed in the West for standard-tool drilling. Wells using the rotary system require larger boilers, of 70 or 80 horsepower. A simple and efficient method for setting up such a boiler is that shown in Fig. 49. This is rated at 40 horsepower, has 42 3-in. by 12-ft. tubes and is hung from two overhead stands of old 6-in. pipe and enclosed with 3000 common red brick. Corrugated iron sheets are then placed so that a space of 18 in. is left between these and the brick work. This space is filled and the top covered with heavy oil-sand that soon cakes when the boiler has been heated and assists materially in reducing the loss by radiation.
The locomotive type of firebox boilers is used extensively in the eastern part of the United States, where good boiler-water may usually be obtained. They possess the advantage that they may be quickly installed and fired, and, for this reason, find occasional use in the West, when gushers or breakdowns of regular plants bring about an urgent need for quick service ; but aside from such conditions their cost and the difficulty encountered in cleaning them have pre vented a more extensive use in the West, where alkaline waters cause scaling and render it necessary that boilers be frequently cleaned.
Of course the fuels used are 'nearly always either oil or gas, except with wildcat wells remote from a field. In burning oil, efficiency is
largely a matter of proper atomization, accomplished by the use of live steam. Fig. 50 illustrates a form of burner in common use that may be made of ordinary materials. The live steam coming from the pointed end of the steam-line inside• the I-in, oil-line atomizes the oil and the two together pass out of the burner through a long, narrow slot, deflected downwards in order to keep the direct flame from impinging on the boiler sheet. The exact position of the pointed end of the steam-line inside that carrying the oil is found experimentally, and so adjusted that it serves to regulate the fire automatically. As the pressure in the boiler increases a greater volume of steam is forced from the end of this pipe, retarding the flow of oil and decreasing the heat applied under the boiler. When the pressure has fallen off, as a result of the lessened heat, more oil finds its way to the burner and the heat increases.
When gas is used instead of oil its maximum fuel value is obtained only by securing the proper mixture of gas and air, so that the flame is a clear blue in color with as little yellow as possible. Several types of burners are manufactured that may be regulated so as to obtain a perfect mixture. A simple burner may be made by placing the gas-line inside of a larger pipe, as is done with the steam pipe in the oil burner. The larger pipe has a number of holes drilled in it through which the air for mixing with the gas is admitted. Still another burner is that shown in Fig. 51, by which the gas and air before igniting mix in the larger pipe, set in brick work.
For carrying steam from the boiler to the engine a 2-in. line usually suffices for standard tool work, but where the drilling is being carried on by the rotary or circulating methods, this is increased to 3 inches.
Lubrication of steam cylinders is accomplished by the use of some of the various forms of pressure-lubricators, either directly at the rig or, when a central plant supplies steam for a number of wells, from a lubricator at the plant. The latter method is unquestionably the more economical and efficient as it insures com plete atomization of the heavy cylinder oil. When smaller lubricators at each well are used, a considerably smaller amount of oil is required if the small pipe carrying the oil from the lubri cator into the steam-line is not merely tapped into the steam-line but is carried half the dis tance across the inside, and then turned up, as in Fig. 52, so that it becomes heated and more readily before passing into the steam cylinder.