PUMPS AND PUMPING MACHINERY or water under high pressure. The hydraulic ram is an example of the first group. It was originally designed by Whitehurst, a watchmaker of Derby, England, in 1772, and subsequently perfected by Montgolfier, the famous French balloonist, in 1796. It consists of a supply pipe (a); an air-chamber (b) attached to the upper side of the pipe (a), and fitted with a valve (c) at the pipe opening; a valve (d) at the end of the supply pipe, and a vertical pipe (e), opening freely into the air-chamber, through which the water is raised to the desired elevation. The device operates as follows: The valve (d) is made just heavy enough to drop and open the lower end of the pipe (a) when the water filling the pipe is at rest. Now assume that this valve opens, allowing the water in (a) to run out. This water gradually acquires an increasing momentum, which finally carries the valve up against its seat and closes the outlet. The water in FIG. 10. Sectional View of Hydraulic Ram. (a) is thus brought suddenly to a state of rest and a part of it rushes into the air-chamber (b) through the valve (c). But, the instant the water in (a) is again in a state of rest, the valve (d) drops again, opens the outlet, allows the water to run out, and is again closed when the increasing pressure is strong enough, bringing the water again to a sudden halt and forcing some more of it into the air-chamber, thence by the elasticity of the air cushion (b) to be pushed upward through the pipe (e) to the point of delivery - and thus the cycle is continued. The action of the valve (c) prevents the return of the water from the airchamber to the pipe (a). This device is adapted to numerous locations and will operate automatically and continuously, without any attention whatever, so long as the surface of the water at the source of supply is kept at the same elevation so as to insure a uniform pressure against the valve (d). When the perpendicular distance from the source of supply to the valve (d) is small, and the water is required to be raised to a comparatively great height, pipe (a) must not only have a considerable fall but must be of larger diameter, and be of sufficient length to prevent the water from being thrown back into the source of supply by the shock when the valve (d) closes. It is also necessary to maintain the supply of air in the air-chamber, which in time, under the great pressure, becomes depleted by being dissolved in the water. In small rams a sufficient amount of air enters through the valve (d), but in rams of considerable size a small snifting valve," attached to another chamber immediately below the air chamber, automatically supplies the additional air whenever it is 9 The jet various manufacturing processes. pumps operating with high pressure water are known commercially also as "eductors." 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 square 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 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, elevator pumps, hydraulic pressure pumps and the like. Practically all are direct-acting pumps operated by steam. They are built both in the horizontal and upright forms. One of the first American pumps designed designed for high-duty waterworks service was the "Worthington direct-acting duplex steam pump." It consists 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 operating its own slide valve, as in the simplex pump, operates the slide valve of the adjoining cylinder. 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 motion 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 mechanism, 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 expansive energy of the steam thus cut off. Therefore 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 connections, 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 engines. 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 pressure 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 efficiency 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 opposite to each other, are two hemispherical recesses. 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 FIG. 11.-Sectional View of Worthington High Duty Pumping Engine. 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 engines was still further increased, and the entire arrangement, from the power-producing to the pumping ends, was made to represent the highest perfection of modern pumping machinery, 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 power 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 cylinders are called "compensating cylinders." When the engines are used for pumping water, they are filled with water, and when used for pumping 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 Views of Large V.T.E. Pumping Engines installed for City of Cleveland, Ohio, by Allis-Chalmers Manufacturing Company PUMPS AND PUMPING MACHINERY fits closely in the air cylinder. Therefore, the pressure per square inch on the accumulatorram and also in the compensating cylinders 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 accumulator-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 beginning 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 11 For the sake of economy in floor space most high-duty pumps are built in the upright or vertical form, the steam sylinders at the top, and the pump cylinders below. With the exception of the Worthington, which still remains 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; weighing, for instance, in the Holly waterworks pumps up to 32 tons each, and each pump carrying two such fly-wheels. The term "duty" represents the work done by a steam pumping engine expressed in millions of pounds of water lifted to the height of one foot by the consumption of 100 pounds of coal, 1,000 pounds of dry steam, or by FIG. 12.-Pumps and posing its advance with the full pressure of the accumulator load. As the plunger-rod advances outward, the angle between itself and the ram is increased gradually to 90 degrees. The rams recede into their cylinders, and their pressure against the rod is decreased until the pump plunger-rod has reached the halfway point of its stroke, when the rams will be at right angles to it-a position in which they neither retard nor advance its movement. As the pump plunger-rod continues on its outward stroke, the angle between itself and the rams is again decreased, but now the rams, pointing in the opposite direction, emerge from their cylinders, and exert their power to push the plunger onward to the termination of its outward stroke. It is obvious that similar conditions obtain during the return stroke of the plunger, the effect of the action being to store up power during the early part of the stroke, either forward or backward, when the steam is under its greatest pressure, and to release it at the end of the stroke, when the pressure in the steam cylinder has fallen away to its lowest point, that is, below the amount necessary to move the plunger against the pressure of the water column. The Worthington pumps with this attachment and the use of multiple expansion steam engines operate with absolute freedom from the noise and shock so characteristic of the crank and fly-wheel machines. Pumping Machines, S 1,000,000 British thermal units (B. T. U.). On account of the variable quality of coal, the two last-named constants give the more correct results, and are the values now employed in determining the comparative efficiencies of pumping engines, which range from 20.6 per cent for the high-duty engines, to about 0.13 per cent for jet pumps. During the last 100 years, the development of pumping engines has increased their duty from about 5,000,000 foot-pounds for the Newcomen atmospheric engines, to over 170,000,000 foot-pounds for the crank and fly-wheel, or duplex triple expansion pumping engines of the latest construction. Somewhat of an idea of the difference between the first duplex Worthington pumping engines and those of their latest construction may be obtained by comparing that of the Charlestown, Mass., waterworks, with its capacity of 5,000,000 gallons per day, with the installation at the Baltimore, Md., waterworks high service pumping station, which delivers 18,000,000 gallons per day. The former gave a duty of 70,000,000 foot-pounds, while the duty of the latter exceeded 140,000,000 foot-pounds per 1,000 pounds of dry steam. Hydraulic pressure pumps are designed as a rule for driving water into an accumulator, whence it may be drawn for power service in mains, or for use in hydraulic presses (q.v.), hydraulic cranes (q.v.), and similar machines. |