1246

THEORY AND PRACTICE OF ENGINEERING.

Book II.

Fig. 1957. SINGLE CONDENSING ENGINE.

nil—u

Fig. 1958.

When the piston isat the top this valvecloses, and that ofthe condenser opens.

The air-pump :during this and thesucceeding opera-tions is worked bythe beam, and ateach stroke of thepiston makes asimultaneous move-ment, and thus isenabled to pumpout the air and waterwhich is the resultof each condensingoperation. G is afoot-valve betweenthe condenser andthe air-pump, M,which has a dis-charge valve at Q,through which theair and hot waterare forced into thehot well, shown at

K : a pipe at N constantly supplies the cistern whichcontains the condenser and air-pump with cold water.

The condenser has a flow valve at H : at the end of apipe is a rose, which admits the jet, through which thecold water passes into B, and this is forced into it, andmade to spread through the steam as much as possible, for the purpose of speedily con-densing it.

The diameter of the cylinder should be half its height, and the velocity of the piston infeet per minute ninety-eight times the square root of the length of the stroke: thesteam passages should be equal to the area of the cylinder multiplied by the velocityof the piston per minute, and divided by 4800. The air-pump should have half thediameter, and half the length of stroke of the cylinder, or should be one-eighth of thedimensions of the cylinder, and the condenser should be equal to it. The quantity ofsteam is ascertained by multiplying the number of feet contained in the area of the cylinderby half the velocity in feet, adding one-tenth for waste; this, divided by the column ofsteam of equal force to that contained in the boiler, gives the quantity of water required perminute for the creation of stfeam, from whence the proportions given to the boiler are estab-lished : with the pressure of two pounds per circular inch on the valve, the divisor will be1497. The water for the purposes of injection will be twenty-four times that required forsteam; consequently the diameter of the pipe used for this purpose must be about athirty-sixth of the diameter of the cylinder : usually the force of the steam in the boilerequals 35 inches of mercury, that of the steam in an uncondensed state 3*7 inches. Tofind the effective power of such an engine, or the number of pounds raised a foot high perminute, multiply 6*66 (which expresses the number of pounds of the mean effectivepressure on the piston) by the square of the diameter of the piston in inches, and by halfthe velocity in feet per ininute: the product is the effective powei ; this divided by 33000gives the horse-power.

Double-acting Steam Engine . — The steam cylinder is enclosed in a jacket or casing ofcast-iron, a trifle larger than the cylinder, and the space between them is supplied withsteam, to keep the temperature of the cylinder as near to that of the steam as possible.The working beam is supported by a cast-iron column, and is connected to the piston-rod by the parallel motion: the other end of the beam gives a rotary motion to thecrank shafts, by' means of a connecting rod, the lower part of which is attached to thecrank. The steam enters at S, passes through the top valve, and acting on the pistonforces it down; before it arrives at the bottom of the cylinder, the plug on the rod Rcomes in contact with a lever, shuts one valve, and opens another ; the steam thencontinues its course down the pipe S, acts on the bottom of the piston, and forces it up tothe top of the cylinder, while the steam, which forced it down, escapes into the condenserB, where it meets with a jet of cold water, is condensed, and then cleared away by theaction of the air-pump A, which is worked by the rod R. The cistern is supplied with