AIR-COMPRESSORS. Improvements in apparatus for compressing air have recently been made. ehiefly in the direction of increasing the speed of rotation, so as to lessen the size and consequent first cost of it machine to do a given quantity of work. The limitation to the speed of an air-compressor has generally been that of the motion of the air-valves, which automatically open and shut with each reversal of the position. To overcome this limitation positive air-valves have been introduced, which receive their motion by mechanical connection with some moving isn't of the engine. Some large blowing-engines for Bessemer steel-works have been thus constructed. The problem of a positive valve-movement, as related to the suction-valves, is a simple one, but as related to the discharge-valves is difficult of solu tion. The difficulty of the problem arises from the fact that the discharge-valves should not open at a fixed point in the stroke. but at a point depending upon the pressure of the air carried, upon the altitude above sett-level, the barometric pressure, and other factors be yond control.
The Rand Drill Company's 1 and 2 illustrate the Halsey gear as made by the Rand Drill Company, which is designed to meet the varied requirements imposed by the discharge-valve. It retains the poppet-valve, which experience has shown to be peculiarly adapted to the requirements of air-compressors, for the reason that such valves have little tendency to wear leaky, and, moreover, any slight leak that may develop is easily repaired by hand-grinding. Fig. 1 is a sectional view of an air-cylinder with the gear applied. The principle of this gear is very simple. The usual form of valve chatters because the air to the letters on the cut, A is the cold-water inlet; B, the cold-water discharge; C. the jacket drain ; D, oil-hole for oil-cup; I]. air-inlet; F, air-delivery ; 6, inlet-valves; H, delivery valves ; J, cold-water jacket. The air-inlet valves are large metallic rings, Fig.
5, which open and close by the natural momentum given to the valve by the movement of the piston. A study of the cut will show that when the piston is moving in one direction, the ring-valve on that face of the piston which is to ward the direction of movement is closed, while that on the other face is open.
This is as it should be, in order to discharge the compressed air from one end of the cylinder while taking in the free air at the other. The position of each valve is almost instantaneously reversed at the point when the stroke is reversed. This change of position takes place without springs or other influence than the nat ural momentum of a piece of metal which is carried in one direction. and is instantly reversed.
The large ring air-inlet valves admit of a large area of inlet with but a small throw of valve, thus quickly opening a large supply port, and enabling a compressor to run at high speed without a reduction of efficiency. and with safety to the quick-moving parts. There being no inlet-valves in the heads of the air-cylinder, the space otherwise occupied by these valves is filled with cold water, thus presenting a cooling surface to the compressed air near the end of the stroke when the air is hottest. This gives all the advantages of cooling by water-in jection, without the disadvantages incident upon bad water, and the necessity of moving a body of water back and forth in the cylinder. The dis charge-valves on the Ingersoll-Sergeant compressors are shown in Fig. 6. Fig. 7 illustrates the unloading device and regulator as applied to the Ingersoll-Sergeant air-compressor. The purpose of this unloading device is to maintain a uniform air-pressure in the receiver and a uniform speed of engine. notwithstanding the consumption of the air, and to do this without waste of power or attention on the part of the en gineer. A weighted valve of safety-valve pattern is attached to the air-cylinder, and is connected with the air-reeeiver, and with a on each end of the also with a balanced throttle-valve in the steam-pipe. When the pressure of the air gets above the desired point in the receiver, the valve is lifted and the air is exhausted from be hind the discharge-valves, thus letting the compressed air at full-receiver pressure into the cylinder at both ends, and balancing the engine. At the same instant the compressed air is exhausted from the little piston connected with the balanced steam-valve and the steam is automatically throttled, so that only enough steam is admitted to keep the engine turning around, or to overcome the friction. no work being done. When the compressor is un loaded, it is evident that the function of the air-piston is merely to force the compressed air through the diseharge-valves and passar.es from one end to the other until more com pressed air is required, this being indicated by a fall in the receiver-pressure. The weighted valve now closes, and the small connecting-pipes are instantly filled with compressed air ; the steam-valve automatically opens. and the compression goes on in the regular way. Another function of this device is to prevent the compressor from stopping or getting on the center. Direct-acting compressors are liable to center when doing work at slow speed.