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Riveting Has a Twofold Meaning for the Patriotic Workers at Hog Island, Every Rivet in a Ship Plate. Serving to Rivet Democracy's Ideals on the World N expediting the construction of ships at Hog island extensive use of compressed air was recognized as a vital factor and considerable atten- tion was given to this phase of the work in planning the huge yard last year. As a result there is at Hog island today, the second largest compressed air plant in the world, planned and_ built under supervision of several of the country's most eminent engineers. The plant was planned to supply com- pressed air at 100 pounds initial pres- sure. It comprises five separate air compressor units which supply the ship- ways and shops and two smaller units which supply the marginal wharf. By dividing the air compressing capacity of the yard into units and inserting valves iN a main pipe running along the heads of the slips and wet basins the danger of a shutdown of the entire air system IS. practically eliminated. The .five larger compressor units are located at about the center of each of the five Stoups of 10 ways, while the two re- maining units are along the marginal Wharf, each serving half of the total number of eight wet basins. These Various compressor houses also serve as high voltage substations. Leading from each of the compressor houses along the shipways is a 12-inck Pipe through which the air is fed into a 10-inch main, extending parallel to and 98 feet from the heads of the slips for more than a mile. This main distributes the air into 6-inch pipes, one of which runs on each side of the keel blocks in each slip. A tee and manifold with six. outlet cocks. is inserted in these pipes at 20-foot intervals along the length of the keel. Another main, 6 inches in diameter and connected to the larger one, extends along the marginal wharf, a distance of more than a half mile, and 3-inch branches are taken down on each side of the wet basin piers. Outlets similar to those on the building slips are inserted in these branches. Provision for expansion and inspection is made by the introduction of U-bends and the use of box trenches along the main lines. Compressed air also is used extensive- ly by the shop group and it is supplied by tapping the 10-inch main and leading a 6-inch branch back and across the front of the group, where suitable exten- sions are made to each shop. Description of Equipment The five larger units are of identical type and each is equipped with three Ingersoll-Rand air compressors. Two of these compressors are 40 and 25%4x 30 inches, direct connected to a 1020- horsepower, General Electric 400-volt, 3- phase, 60-cycle synchronous motor, having a speed of 138% revolutions per minute. The actual delivered capacity of each is 5320 cubic. feet of free air per minute. The third compressor is 28 and 171%4.x21 inches, direct connected to a 450-horsepower, General Electric 4000- volt, 3-phase, 60-cycle synchronous motor, ng a speed of 180 revolutions per havi : The actual delivery capacity of minute. 331 this unit is 2275 cubic feet making the total capacity of the plant 12,915 cubic feet of free air per minute. Some of the difficulfies not infre- quently arising in the operation of air tools are due to moisture in the air, or "wet air." This moisture on being car- ried into the machines tends to wash away the lubricant and to increase wear by leaving bare surfaces in contact. It also condenses and collects in the pipe lines interfering with the free passage of air, and may freeze and burst the pipes in cold weather. This disadvan- tage is particularly serious in work in the open. To eliminate it, each of the compressors has been equipped with an after-cooler which serves to remove the moisture from the compressed air be- fore it enters the distribution system. This is accomplished by cooling the air to a point at which the moisture will condense and accumulate in suitable receptacles to be drained at intervals. The after-coolers serving the two large compressors in each plant along the ways have a cooling surface of approxi- mately 1005 square feet, and the one serving the smaller compressor 505 feet. Intake air is drawn from the outside through cast iron or salt-glazed pipe cast in the concrete foundations and termi- nating in sheet metal cowls 12 or 13 feet above the ground. A suitable piping system is installed for leading the dis- charge air from the compressors to a receiver which acts as a separator and serves to dampen pulsations for the complete unit. Cooling water for the