Mechanical engineers' handbook,

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1922 Excerpt: ...of 8 ft. per sec. and the airpump connection should be at least twice that of the hot-well pump suction, which should be figured for about 4 ft. per sec. AIR PUMPS The amount of air in feed water varies from 0.75 to 5 per cent, by volume at atmospheric temperature and pressure. If closed heaters are used, all of the air passes through the boilers and prime movers into the condenser. If open heaters are used, the air in the feed water (at 200 deg. falir.) should not be over 1 per cent. The leakage in surface condensers is an extremely variable quantity, ranging from 1 per cent, in tight condensers to 25 per cent, or more in condensers in poor condition. The average leakage is from 5 to 10 per cent, of the volume of the feed water. The volume of air passing into the air pump may be calculated as follows, if the volume of free air is known: V = Vfa(l, + 460)/(P;-P.)(U + 460), where V = volume of the air in vacuum, cu. ft.; V, = volume of the air at atmospheric pressure and temperature entering the condenser, cu. ft.; Pa = atmospheric pressure, Pc = total pressure at pump suction, and P, = pressure of vapor at t,, all in in. of mercury, absolute; t, = temperature at pump suction, and ta = atmospheric temperature, both in deg. fahr. As there is always leakage through glands, pipes or joints, the air pump must have a displacement greater than that given by the above formula. In practice the dry-air pump has a displacement of from 10 to 60 times the volume of the condensed steam. The average ratio for engines is about 20, and for steam turbines 25 at low vacua and 35 to 45 at high vacua. If the air pump must remove the condensed steam, allowance is made therefor. Fig. 5 shows the relation between the temperature in the air-pump suction pipe and the volume of satur...