SECTION IX. OF THE APPLICATION OF STEAM ENGINES TO DIFFERENT PURPOSES. 569.-The immense variety of objects to which steam power is or may be applied, renders it necessary to confine our attention to the most prominent ones for illustration. These are to raising water; to impelling machinery for mining, manufacturing, and agricultural purposes; and to land carriage: the application to navigation being so distinct and important, as to require a separate section. (See Sect. X.) Of raising Water. 570.-Water is generally raised by means of pumps of the lifting or forcing species. The stroke of a pump should not exceed about eight feet, otherwise the air disengaged from the water, the escape by the bucket or piston, and the defect of pressure on the fluid which is rising after the piston, becomes greater than the escape by the valves. The velocity of the piston should not exceed ninety-eight times the square root of the length of the stroke, (art. 342.) 571.-Owing to the escape at the valves and the disengagement of air, the quantity of water a pump in the best order delivers at one stroke is .95 l d x ·7854 ·00518 / d2 = the quantity in cubic feet; when l is the length of the stroke in feet, and d the diameter of the pump in inches; or substituting half the velocity for 1, it gives the cubic feet per minute. 572.-The power required to raise water a given height, is found by taking the exact height in feet, from the surface of the water to the point of discharge, and adding one foot and a half for each lift, for the force required to give the water the velocity; and also add onetwentieth of the height for the friction of the piston, and call this quantity in feet h; then 341 h d2 = the load in pounds. Whence, if P = the mean effective force on the steam piston in pounds per circular inch, we have d (_·341 h _)2 = D, ' ' the diameter of the steam piston in inches.* And as 180 feet per minute is a very good velocity for raising water, if Q be the quantity in cubic feet, Example. Suppose it be required to raise eighty cubic feet of water per minute by a single acting engine, the mean effectual pressure of the steam being eleven pounds per circular inch, and the lift 149 fathoms in six lifts. In this case 149 fathoms = 894 feet; (5054-171 )* = 72 inches nearly, for the diameter of the cylinder; and (2·15 × 80 )+ = 13.115 inches = the diameter of the pump; the velocity being 180 feet per minute. Both these diameters ought to be increased five per cent for contingencies. Drainage of Mines. 573.-In this country the drainage of mines is a subject of vast importance. It is mines which supply the means of employing steam power, and also a large proportion of the materials on which that power is expended. To persons accustomed to mines, it is seldom necessary to state those principles which should direct them in the choice of engines. The absolute necessity of an economical system of drainage is felt and acted upon, and it is by comparison of annual expense, and not by a comparison of the effect, from a given quantity of fuel, that this economy should be estimated. A mine engine should be simple in construction, durable in use, and made with a view to easy repair. When coals are not expensive, the most simple methods are the most economical; for instance, at the mouth of a coal pit the extra consumption of coals is of less value than the extra wear and tear of a complex engine. 574.-The modes of draining mines are dependent on the nature of the district where they are situated. If it be mountainous, a subterraneous channel or day level drift,* may be made, from the lowest part of the mine to terminate in the nearest valley, to carry off the water, and it is only when this method is impracticable that water is raised by power, and even then the water is raised no higher than to where a day level drift can be obtained. But it frequently happens that the flatness of the country renders any other method impracticable, than that of raising the water to the surface. For example in the coal-field of Northumberland and Durham, many of the large double pits exceed one hundred fathoms in depth, and some are nearly 150 fathoms deep, with no means of drainage by levels. These pits therefore require very powerful engines, and lately they have chiefly erected double engines, some of which are above one hundred horses' power; the largest I saw there was one on the south side of the Tyne which was working with 160 horses' power, * In Cornwall and Devon it is called an adit, in some other places a sough. and was capable of exerting the power of 200 horses in action at once. In Cornwall they have some larger engines, but two engines should always be preferred, when the cylinder of one engine would exceed about sixty inches in diameter, for two engines give many advantages. 575.-When double engines are used for lifting water, they generally work one set of pumps by the outward end of the beam, and another set by a diagonal spear from the piston rod end. And in cases where it has not been convenient to divide the pumps into two sets, the ascending motion of the piston has been employed to raise a weight equal to the pressure of half the column of water in the pumps, but for such cases a single engine should be preferred. 576.-The following table will give some idea of the work done by a given quantity of fuel, and of the nature of the engines most approved of in Cornwall; the results however can be correct only through the different errors of the mode of estimation balancing one another, for the weight of the column of water is less than the resistance, and the counter only registers the strokes and not the actual quantity of water raised.* * In the year 1811, a number of the respectable proprietors of the valuable tin and copper mines in Cornwall, resolved that the work which their respective steam engines were performing, should be ascertained, as it was suspected that some of them might not be doing duty adequate to the consumption of fuel; and for the greater certainty of attaining their object, it was agreed that a counter should be attached to each engine, (art. 563,) and all the engines be put under the superintendance of some respectable engineer, who should report monthly, the following particulars in columns: viz. The name of the mine; the size of the working cylinder; whether working single or double; the load per square inch in the cylinder; length of stroke in the cylinder; the number of pump lifts; the depth in fathoms of each lift; diameter of pumps in inches; time worked; consumption of coals in bushels; number of strokes during the time; length of stroke in pump; load in pounds; pounds lifted one foot high by a bushel of coals; number of strokes per minute; and lastly, a column for names of engineer and remarks. Messrs. Thomas and John Lean were appointed to the general superintendance; and the different proprietors, as well as the regular engineers of the respective mines, engaged to give them every facility and assistance in their power. The first monthly report was for August 1811. See Philo. Mag. Vol. XLVI. p. 116. ( 5054-171 ) = 72 inches nearly, for the diameter of the cylinder; and (2·15 × 80 )† 13.115 inches = the diameter of the pump; the velocity being 180 feet per minute. Both these diameters ought to be increased five per cent for contingencies. = Drainage of Mines. 573.—In this country the drainage of mines is a subject of vast importance. It is mines which supply the means of employing steam power, and also a large proportion of the materials on which that power is expended. To persons accustomed to mines, it is seldom necessary to state those principles which should direct them in the choice of engines. The absolute necessity of an economical system of drainage is felt and acted upon, and it is by comparison of annual expense, and not by a comparison of the effect, from a given quantity of fuel, that this economy should be estimated. A mine engine should be simple in construction, durable in use, and made with a view to easy repair. When coals are not expensive, the most simple methods are the most economical; for instance, at the mouth of a coal pit the extra consumption of coals is of less value than the extra wear and tear of a complex engine. 574.-The modes of draining mines are dependent on the nature of the district where they are situated. If it be mountainous, a subterraneous channel or day level drift,* may be made, from the lowest part of the mine to terminate in the nearest valley, to carry off the water, and it is only when this method is impracticable that water is raised by power, and even then the water is raised no higher than to where a day level drift can be obtained. But it frequently happens that the flatness of the country renders any other method impracticable, than that of raising the water to the surface. For example in the coal-field of Northumberland and Durham, many of the large double pits exceed one hundred fathoms in depth, and some are nearly 150 fathoms deep, with no means of drainage by levels. These pits therefore require very powerful engines, and lately they have chiefly erected double engines, some of which are above one hundred horses' power; the largest I saw there was one on the south side of the Tyne which was working with 160 horses' power, • In Cornwall and Devon it is called an adit, in some other places a sough. |