jet pumps operating with steam or com pressed air are termed They are ut tise for spraying or atomising liquids in various manufacturing processes. The jet pumps operating with high pressure water are known commercially also as eeductors.D They have no valves or other moving parts, and are not subject to wear and tear, and, being also of low first cost, are very economical where a small supply of high-pressure water can be commanded. The construction is extremely simple. The high-pressure pipe is placed in the centre axially of a larger flow or discharge pipe and fitted with a conical mouthpiece. The discharge pipe is narrowed at the opening of the jet and then expanded gradually to its full size. With a three-inch discharge pipe and a one and one-half-inch jet pipe operating with a pressure of 40 pounds to the scipare inch (about 90 feet head) the discharge will amount to 5,000 gallons per hour. For lifting water the pressure in pounds per square inch of the jet opening is made two and one-half times the elevation in feet. Thus if the lift is 20 feet the pressure required is 50 pounds. The eductor works well on the level of discharge if S the suction lift is not more than 15 feet.
The so-called (high-duty( pumps are those in use for heavy work against great pressure. They include waterworks pumps, mine pumps, fire-service pumps, elevatorpumps, hydraulic pressure pumps and the like. Practically all are direct-acting pumps operated by steam. They are built both in the horizon tal and upright forms. One of the first American pumps designed for high-duty waterworks service was the (Worthington direct-acting duplex steam pump.* It con sists of two double-acting plunger pumps placed side by side with the piston-rod of each steam cylinder connected by a lever to the slide valve of the adjoining steam cylinder, so that the movement of each piston instead of operat ing its own slide valve, as in the simplex pump, operates the slide valve of the adjoining cylin der. The valve motion is so adjusted that just before the piston of one cylinder has finished its stroke, the piston of the other begins its movement. The load of the water column is then taken up alternately and produces a steady flow without serious strains, harshness of mo tion and noise, which characterize the action of the simplex pumps, in which the water column is started into motion at the beginning, and arrested at the end of each stroke of the piston. Although the simplicity of their me chanism, together with the cheapness of their first cost and the certainty of their action, placed them at the head of all the machines of their class, when considered from a mechanical standpoint, the loss of economy in the use of steam continued to militate against their general use for heavy duty purposes. Their light weight prevented the cutting off of the steam in the steam cylinder so as to complete the stroke of the piston by the aid of the ex pansive energy of the steam thus cut off. There fore the steam applied to move the pistons had to be applied in sufficient quantity and pressure to overcome the weight of the water column and its friction through the pump and connec tions, at the very beginning of the stroke, and maintained without diminution throughout the stroke, up to its termination, since a falling off in either volume or pressure during any part of the stroke would have stopped the action of the pump instantly. This defect, however, was completely eliminated by applying to them the principle of multiple expansion in the use of steam in compound condensing steam en gines. Another steam cylinder was added to the end of the one already in use, and placed in a direct line with it so that the high pres sure steam admitted to the first and smaller cylinder, after moving its piston, was exhausted behind the piston of the large cylinder upon its return stroke. Still further economy was produced in the larger compound engines by using a condenser to create a vacuum in the large steam cylinder, thus bringing the effi ciency fully up to that of the best high-duty rotative engines of the most important pump rod which is extended for this purpose through the outer end of the pump chamber. On the
end of this rod is fastened a cross-head which moves in guides attached to the outer end of the pump. On this cross-head, and situated oppo site to each other, are two hemispherical re cesses. On the guide plates are two journal boxes, one above and the other below the plunger-rod, equidistant from it, and placed at a point equal to the half stroke of the cross-head. Each journal box carries a short cylinder hung on trunnions, which allow the cylinder to swing in unison with the motion of the plunger rod. In these cylinders are plungers or rams, which pass through a stuff ing plants of the world with yearly records ranging from a duty of 50,000,000 to 120,000,000 foot-pounds per 100 pounds of good coal.
The duty of the Worthington pumping en gines was still further increased, and the en tire arrangement, from the power-producing to the pumping ends, was made to represent the highest perfection of modern pumping ma chinery, by the application of the accumulator, a device originally invented by J. D. Davis, in 1879, and perfected by C. C. Worthington, in 1884. With it the steam may • be cut off in the steam cylinder soon after the beginning of the piston stroke, a part of the cower being stored and brought into play toward the end of the stroke so that the force exerted upon the pump plunger remains uniform through the entire stroke. In a compound direct-acting steam pump, the device is attached to the plunger ing box on the end. The outer ends of the rams have rounded projections which fit into the recesses on the cross-head, which is moved in and out with the plunger, thus tilting the cylinders backward and forward. These cylin ders are called °compensating cylinders." When the engines are used for pumping water, they are filled with water, and when used for pump ing oil, they are filled with oil. The pressure on their rams is produced by connecting the cylinders through their trunnions which are hollow, with an accumulator, carrying a ram which moves up and down as the rams of the cylinder move in and out. This accumulator is of the differential type, the small lower cylinder of which is filled with water or oil, in which the ram moves, while the larger upper cylinder is filled with air. On the top of the accumulator-ram is a large piston-head which fits closely in the air cylinder. Therefore, the pressure per square inch on the accumulator ram and also in the compensating cylin ders is equal to the pressure of the air in the air cylinder per square inch multiplied by the difference between the area of the air piston and that of the accuinulator-ram. It is a matter of calculation and construction, which varies according to the particular service for which a pumping engine is designed; while the pressure in the air cylinder is controlled by the pressure in the main delivery pipe with which the air chamber is connected. The effect of this attachment on the successful operation of high duty pumping engines may be briefly described as follows: At the begin ning of the outward stroke of the pump plunger-rod, the compensating cylinders point inward toward the pump, with their rams at an acute angle with the plunger-rod, and op For the sake of economy in floor space most high-dnty pumps are built in the upright of vertical form, the steam cylinders at the top, and the pump cylinders below. With the ex ception of the Worthington, which still re mains of tandem design, the high, intermediate and low pressure steam cylinders are set side by side in a rank. With the same exception also, most of the high-duty pumps are built to work on a crank shaft carrying fly-wheels, some of which are enormously heavy; weigh ing, for instance, in the Holly waterworks pumps up to 32 tons each, and each pump carry ing two such fly-wheels.