PUMPS, RECIPROCATING. The Worthington High duty Pump.—One of the most important recent inventions in pumping machinery is that of the high-duty attachment to the Worthington duplex pumping-engine, by which engines of the direct-acting, reciprocating type, without fly-wheels, may be caused to store up energy during the first part of the stroke, to be given out toward the end of the stroke, and so utilize the advantages of expansion in the steam-cylinders to the highest degree. This improvement is thus described by Mr. J. T.
Holloway, in a paper presented to the American Society of Mechanical Engineers (Trans., vol. xi.). Fig. I shows a sectional elevation of a compound direct-acting steam-pump, hav ing attached to it what has been called the high-duty attachment. To ordinary compound direct-acting steam-pumps, as usually built, there is attached a plunger-rod which projects through the outer end of the pump chamber, and around which there is the usual stuffing box for packing the same. On the end of this plunger-rod is fastened a cross-head, which moves in guides bolted on the outer end of the pump. On this cross-head and opposite to each other are semi-circular recesses. On the guide plates are cast two journal boxes, one above alai one below the plunger-rod, both equidistant from it, and at a point equal to the half stroke of the cross-head. In these journal boxes are hung two short cylinders on trunnions, which permit the cylinders to swing backward and forward in unison with the plunger-rod. Within these swinging cylinders are plungers, or rams, which pass through a stuffing-box on the end of the cylinder, and on their outer ends they have a rounded pro jection which fits in the semi-circular recesses in the cross-head; and, consequently, as the cross-head moves back and forward, it carries with it these two plungers, which in turn tilt the cylinders back and forward on their trunnions. These swinging cylinders are called " compensating cylinders," and they are filled with the fluid being pumped.
The pressure on the plungers within the compensating cylinders is produced by connect ing these cylinders through their hollow trunnions with an accumulator, the ram of which is free to move up and down as the plungers of the compensating cylinders move in and out. The accumulator used is of the differential type; it has below a small cylinder tilled with water or oil, within which its plunger moves, while above it has a larger cylinder filled with air, and within which there is a piston-head which fits closely to the cylinder, and is at the same time attached to the top of the plunger in the lower cylinder.
By this arrangement it will be seen that the pressure per square inch on the plunger or ram of the accumulator will be the pressure per square inch on the piston-head in the upper cylinder multiplied by the difference between the area of the piston-head and the lower plunger. This difference of areas is a matter of calculation, based upon the particular service for which the pump is constructed. The pressure in the air-cylinder is controlled by the pressure in the main delivery pipe of the pump, as it is connected to that pipe. This con nection with the main has another very important use, as the power exerted by the com pensating cylinders is a very considerable part of the power used in driving the pump plunger at the latter part of its stroke and it will be seen that if for any cause. either by the break ing of the main or otherwise, the load is entirely thrown off the pump, the plunger cannot make a disastrous plunge forward, for the reason that the steam in the steam-cylinder is, by reason of its expansion, too low in pressure to drive it, while the fall of pressure in the main has robbed the accumulating cylinders of their power.
Test of a Worthington Iligh-duty Engine.—Fig. 2 shows a set of three duplex com pound direct-acting pumping-engines, built by Henry R. Worthington for the Artesian Water Co., Memphis, Tenn. The engines, each of which is of 10,000,000 gallons capacity, and works against a head of 250 ft., are essentially the same in principle as the horizontal engines built by the same firm, but are modified to suit the different conditions. The high pressure cylinders are placed on top, and are 30 in. diameter, the low-pressure cylinders steam and water ends, their plungers being connected directly to the main piston-rods. Below the compensating cylinders, and inside the frames, is a balancing device on each piston-rod, which exactly balances the weight of the reciprocating parts. This consists simply of a cylinder through which the piston-rod passes, and is provided with a piston to fit the cylinder, stuffing-boxes being provided at each end above and below. Below this piston is water, which, as the piston descends, is forced out of the cylinder through a pipe against a pressure of air, this air pressure forcing the water back into the cylinder again, and lifting the weight of the reciprocating parts during the up-stroke. The pressure of air for this is restored to the proper amount by means of the auxiliary compressor, when it becomes reduced through leakage.