524

MODERN STEAM PRACTICE,

equals one-fourth of the diameter of the pump; the diameter ofthe air-pump rod equals the diameter of the pump divided by 7.The area of the foot-valve passages in the condenser equals the fullarea of the pump, but for the head-valve passages more is allowed,which is found by multiplying the area of the pump by 1 ‘35; thisresult is only for one end. The area through the gratings for thefoot valves should not be less than the pump area multiplied by - 6i,and for the head valves '83 is the multiplier. Of course more areain the passages and gratings may be allowed, as a large area reducesthe lift of the valves, and renders the wear and tear of the indiarubber less severe. The valve seats are secured to the condenserby ^-inch stud bolts and nuts of Muntz metal. The capacity ofthe condenser is generally about 13 times that of the capacity ofone cylinder, when a condenser is fitted to each, placed side by side.When the condenser is on the opposite side in relation to thecranked shaft, the capacity can be reduced, as the eduction pipethen forms a part of the condenser, and increases the total cubicalcontents. The area of the main discharge pipe equals the area ofthe air pump, or one-half the area for each. The thickness of thecondenser varies from ^ to 1 inch; all the flat surfaces shouldbe strengthened with ribs in the casting. There should be an airvessel formed in the casting, placed above the head valves, so as tolessen the shock of the ejected water. The diameter of the sniftingvalve varies from 2*4 to 4 inches, and it should be placed as lowdown as possible, so that all the air, water, &c., may be ejected inthe act of blowing through.

Injection valve, &c .—To find the area of the injection pipe,multiply the cubic contents of the cylinder in feet by "4, whichgives the area in square inches for each condenser; the bilge injec-tion may be less than this. The former should be placed as highup and the latter as low down as possible in the condenser.

Surface condensation. — The surface of the tubes, according toHall, should have about 2800 square inches for the condensation of60,000 cubic inches per minute, the quantity of cold water requiredbeing about xo gallons. Some makers give about the same sq. feetof condensing surface as there are sq. feet of heating surface in theboilers (see p. 432). Of course, the pressure of the steam as itenters the condenser is the point to study in considering the amountof surface required; a very general rule is to multiply the total heat-ing surface in the boiler by 75, which gives the number of sq. feet