====================================+=====+======== (1) Length of Stroke |=12= | 16 (in inches) | | ------------------------------------+-----+-------- (2) Greatest No. revolutions per |=70= | 60 minute. | | ------------------------------------+-----+-------- (3) Corresponding Piston travel |=140=| 160 ft. per minute. | | ------------------+-----------------+-----+-------- Approx. |(4) Feet | 308 | 352 actual max. Piston| per minute. | | velocity at full +-----------------+-----+-------- speed, per row |(5) Feet | 5.1 | 5.9 (3) × 2.2. | per second. | | ------------------+-----------------+-----+-------- (6) Net Suction Valve-port area |=56%=| 64% speed regarded necessary for | | this per cent. of Plunger area. | | ------------------------------------+-----+-------- (7) Total Suction Valve Outlet |=56%=| 64% Area under Valves lifted | | 1/2 in. high. | | ------------------------------------+-----+-------- (8) Discharge Valve Area. |2/3 of Suction |Valve Area. ------------------------------------+-------------- By “valve-outlet area,” we mean the vertical cylindrical surface over the outer edge of the valve ports, _i. e._, the distance L multiplied by the circumference at the outer edge of the valve ports _C_, Fig. 8. Thus for a 4-inch valve, with ports inscribed in a 3-1/2-inch circle, whose circumference is 3·5 × 3·1416 = 11 inches; the valve “outlet area” for 1/2-inch lift would be 5-1/2 inches. [Illustration: FIG. 8.] The actual velocity of piston during the middle portion of stroke is from 2.0 to 2.4 (average 2.2) times as great as the piston travel per minute (as determined in experiments by Mr. J. R. Freeman on several duplex pumps of different manufacture). This is because each piston stands still nearly half the time, or while its mate is working, and, moreover, moves more slowly near start and finish of stroke. The words “piston speed” are commonly incorrectly used and refer to “piston travel.” A clear understanding that the actual piston speed is _more than twice as great_ leads to more generous valve design. Large aggregate valve areas are necessary for pumps designed to run as fast as these, and experience has shown that to prevent valve slam at high speed and to accommodate high suction lifts, it is just as important to have a large “valve outlet area” as to have a large area of valve port.