A three inch overboard discharge line, located six feet below the waterline, has ruptured and separated from the hull. What would be the minimum number of strokes per minute required from a 8" x 12" x 12" duplex double acting reciprocating bilge pump, operating at 82% efficiency, to keep the bilge level from continuing to rise? See illustration SF-0034.
⢠Use the SF-0034 table to find the gallons per minute (gpm) entering through a 3-inch hole at 6 feet of head. ⢠Compute the theoretical displacement per stroke of one side of the pump from its dimensions (8" x 12"), then account for duplex double-acting operation. ⢠Apply the pump efficiency (82%) to get actual gpm, then relate gpm = gallons per stroke à strokes per minute.
⢠How many gallons per minute are flooding in through the ruptured line according to the table, and why is that the minimum you must pump out? ⢠Given the cylinder dimensions, how many cubic inches (and then gallons) are moved per stroke on one side, and how does duplex double-acting change that volume per stroke of the pump? ⢠Once you know gallons per stroke and gallons per minute flooding in, what strokes per minute will just balance the inflow after considering 82% efficiency?
⢠Be sure you selected the correct row (3 in) and column (6 ft) from SF-0034. ⢠Convert cubic inches to gallons using the correct factor: 1 gallon â 231 inÂł. ⢠Confirm you multiplied by both cylinders and both directions of stroke for a duplex double-acting pump before applying 82% efficiency.
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