By H.R. CORNELIUS.
In December, 1883, bids were asked for by the United States government on pumping machinery, to remove the water from a dry dock for vessels of large size.
The dimensions of the dock, which is situated on San Pablo Bay, directly opposite the city of Vallejo, are as follows:
Five hundred and twenty-nine feet wide at its widest part, 36 feet deep, with a capacity at mean tide of 9,000,000 gallons.
After receiving the contract, several different sizes of pumps were considered, but the following dimensions were finally chosen: Two 42 inch centrifugal pumps, with runner 66 inches in diameter and discharge pipes 42 inches, each driven direct by a vertical engine with 28 inch diameter cylinder and 24 inch stroke.
These were completed and shipped in June, 1885, on nine cars, constituting a special train, which arrived safely at its destination in the short space of two weeks, and the pumps were there erected on foundations prepared by the government.
From the "Report of the Chief of Bureau of Yards and Docks" I quote the following account of the official tests:
"The board appointed to make the test resolved to fill the dock to about the level that would attain in actual service with a naval ship of second rate in the dock, and the tide at a stage which would give the minimum pumping necessary to free the dock. The level of the 20th altar was considered as the proper point, and the water was admitted through two of the gates of the caisson until this level was reached; they were then closed. The contents of the dock at this point is 5,963,921 gallons.
"The trial was commenced and continued to completion without any interruption in a very satisfactory manner.
"In the separate trials had of each pump, the average discharge per minute was taken of the whole process, and there was a singular uniformity throughout with equal piston speed of the engine.
"It was to be expected, and in a measure realized, that during the first moments of the operations, when the level of the water in the dock was above the center of the runner of the pumps, that the discharge would be proportioned to the work done, where no effort was necessary to maintain a free and full flow through the suction pipes; but as the level passed lower and farther away from the center there was no apparent diminution of the flow, and no noticeable addition to the load imposed on the engine. The variation in piston speed, noted during the trial, was probably due to the variation of the boiler pressure, as it was difficult to preserve an equal pressure, as it rose in spite of great care, owing to the powerful draught and easy steaming qualities of the boilers.
"After the trial of the second pump had been completed the dock was again filled through the caisson, and as both pumps were to be tried, the water was admitted to a level with the 23d altar, containing 7,317,779 gallons, which was seven feet above the center of the pumps; this was in favor of the pumps for the reasons before stated. In this case all the boilers were used.
"Everything moved most admirably, and the performance of these immense machines was almost startling. By watching the water in the dock it could be seen to lower bodily, and so rapidly that it could be detected by the eye without reference to any fixed point.
"The well which communicates with the suction tunnel was open, and the water would rise and fall, full of rapid swirls and eddies, though far above the entrance of these tunnels. Through the man hole in the discharge culvert the issuance from the pipes could be seen, and its volume was beyond conception. It flowed rapidly through the culvert, and its outfall was a solid prism of water, the full size of the tunnel, projecting far into the river.
"During a pumping period of 55 minutes, the dock had been emptied from the twenty-third to two inches above the sixth altar, containing 6,210,698 gallons, an average throughout of 112,922 gallons per minute. At one time, when the revolutions were increased to 160 per minute, the discharge was 137,797 gallons per minute. This is almost a river, and is hardly conceivable. After the pumps were stopped, on this occasion, tests were made with each in succession as to the power of the ejectors with which each is fitted to recharge the pumps.
"The valves in the discharge pipe were closed and steam admitted to the ejector, the pump being still and no water in the gauge glass on the pump casing, which must be full before the pumps will work. The suction pipe of the ejector is only two and a half inches in diameter, the steam pipe one inch in diameter. To fully charge the pumps at this point required filling the pump casing and the suction pipe containing about 2,000 gallons; this was accomplished in four minutes, and when the gauge glass was full the pump operated instantly and with certainty, discharging its full volume of water.
"I went on several occasions down in the valve pits on the ladder of the casing, and to all accessible parts while in motion at its highest speed, and there was no undue vibration, only a uniform murmur of well-balanced parts, and the peculiar clash of water against the sides of the casing as its velocity was checked by the blank spaces in the runner.
"The pumps are noisy while at work, due to the clashing of the water just mentioned, but it affords a means of detecting any faulty arrangements of the runner or unequal discharge from any of its openings. While moving at a uniform speed, this clashing has a tone whose pitch corresponds with that velocity of discharge, and if this tone is lacking in quality, or at all confused, there is want of equality of discharge through the various openings of the runner. To this part I gave close attention, and there was nothing that the ear could detect to indicate aught but the nicest adjustment. The bearings of the runners worked with great smoothness, and did not become at all heated. Through a simple, novel arrangement, these bearings are lubricated and kept cool. There is a constant circulation of water from the pumps by means of a small pipe, which completes a circuit to an annular in the bearings back to the discharge pipe while the pump is in motion, requiring no oil and making it seemingly impossible to heat these bearings.
"The large cast steel valves placed in the embouchement of the casing, it was thought, might act to check the free discharge, and arrangements were provided for raising and keeping them open by a long lever key attached to their axes of revolution, but, to our great surprise, at the first gush from the pumps these valves, weighing nearly 1,500 pounds, were lifted into their recessed chambers, giving an unobstructed opening to the flow, and they floated on its surface unsupported, save by the swiftly flowing water, without a movement, while the pump was in operation.
"The steam-actuated valves in the suction and discharge pipes worked very well, and the water cushion gave a slow, uniform motion, and without shock, either in opening or closing them.
"The engines worked noiselessly, without shock or labor. At no time during the trial was the throttle valve open more than three-eighths of an inch.
"The indicator cards taken at various intervals gave 796 horse power, and the revolutions did not exceed 160 at any time, though it was estimated that 900 horse power and 210 revolutions would be necessary to attain the requisite delivery. So that there is a large reserve of power available at any time.
"The erection of this massive machinery has been admirably done. The parts, as sent from the shops of the contractor, have matched in all cases without interference here; and, when lowered into place, its final adjustment was then made without the use of chisel or file, and has never been touched since.
"The joints of the steam and water connections were perfect, and the method of concentrating all valves, waste pipes, and important movements at the post of the engineer in charge gives him complete control of the whole system of each engine and pump without leaving his place, and reduces to a minimum the necessary attendance. All the parts are strong and of excellent design and workmanship; simple, and without ornamentation.
"Looking down upon them from a level of the pump house gallery, they are impressive and massive in their simplicity.
"The government is well worth of congratulation in possessing the largest pumping machinery of this type and of the greatest capacity in the world, and the contractors have reason to be proud of their work." - Proc. Eng. Club.
Built by the Southwark Foundry and Machine Company, of Philadelphia.