Some of the pits at first made were too narrow to admit pumps with volute casing and with a single wheel large enough to attain the required speed. In such cases the pumps have been compounded, as shown in Fig. 4, so as to reduce the speed of ration and diminish the size of the wheels and casing. In the compound pump here shown, with two revolving wheels, I?, the main casing is made in five parts, consisting or three hoops or rings, and two intervening diaphragm plates, all secured together by external bolts. The driving shaft from the top of the pit is coupled to the pump spindle at C. A charging pipe, P, is carried down from the top of the pit. as in the case of Fig. 1, previously described, The foot of the delivery main, .31, is surrounded by an annular air-vessel, A. The water is drawn by suction into the top chamber, 1', whence it passes downward through the two wheels or runners, 1Z, and out through the discharge chamber D, the delivery valve P, and the rising main, The two shrouded wheels have each five curved vanes, as shown in the plan, Fig. 7. The exact shape of the curves is believed by the writer to be a matter of very little importance in practice ; and the number of the vanes, whether two or six, does not make much difference in a high-speed pump. Curved throat pieces and tangential tips to the vanes are found in such cases to be of practical value so far only as they tend to obviate friction and consequent slight loss of power. The diaphragm above the upper runner is a plain flat plate ; but the intermediate diaphragm between the two runners is made with fixed guide blades on its upper side, for leading the water back from the circumference of the upper wheel to the central inlet into the lower. Besides the double inlet at 85, two more inlet orifices are pro vided in the top cover at 1 I, Fig. 6, for convenience of attaching additional suction pipes in different cases ; but it is not often that all four inlets are required. The delivery valve is arranged to swing clear of the ascending column of water; the area of passage is here con tracted and determines the pump's capacity. In all other parts the area of passage is made much larger. Except for avoiding concussion from the water in stopping the pump, the air-vessel. A, may seem superfluous in a continuously acting pump ; but it is not so, and air vessels are now applied by the writer in all cases for deep pumping. The seat of the delivery valve. is raised so as to leave an annular space all round it, for catching any gravel deposited in the valve chamber ; this space is commonly made much larger than shown in the drawing. The bottom bearing of the pump spindle at B. Fig. 4, is simply a hole bored in the base plate. There is no strain upon it when the wheels are carefully balanced. It is, of course, exposed to sand and gravel, but these do not seem to have much effect upon bear ings of steel running in cast-iron ; either the sand is at once pulverized and washed out, or in some other way attrition is prevented. Similarly the throats of the inlet orifices in the revolving wheels do not seem to wear after they have worn themselves out of contact.
Balanced Pump with Single Lateral Inlet. —In Figs. 8 and 9 is shown the construction now adopted by the author for pumps with a single inlet at one side, a form most suitable for the requirements of the Pacific Coast, and essential in many cases. The drawing shows a pump of 12-in. bore arranged for a head of 30 ft. The wheel consists of a curved disk, 1), shaped so as to deflect the water gradually from the center to the circumference. On the face of the disk are formed the vanes, U and IT, of unequal area. On the back of the disk are also vanes. .7.V. Holes, (1, are made through the disk, so that any water passing over the circum ference may circulate in this way. An equal or nearly equal centrifugal action is thus set up on each side of the disk, and there is no axial thrust, the pinup being balanced in the same way as though there were double inlets, one at each side. In this arrangement the suction pipe is easily removed, and can be hoisted vertically clear of the pump. The water
passages are also more free, and of large area until the disk is reached. In order to guard the spindle bearing from sand and grit, the packing is placed at inside the main bearing Ii, which acts also as a gland for compressing the packing. This arrangement is now employed in all the various modifications of centrifugal pumps from the author's designs, and in working permits no leak of either air or water, and the pack ing seldom needs renewal. The pumps are characterized by and steadiness of running. and an absence of the pulsation or jar common with free or open vanes, or with shrouded wheels. Such jar is often caused by au obtuse or imperfectly formed throat piece at T, especially with shrouded wheels, the radial flow being interrupted at that point.
Bulkhead Pumps.-11, Fig. 10 is shown a plan of a pair of centrifugal pumps arranged for driving the water through a bulkhead against a head varying from nothing to 10 ft. The pumps are submerged to a sufficient depth to require uo charging, and consequently no valves are necessary. The area of the two discharge nozzles is 150 sq. in. each. and the quantity of water delivered is 500,000 to 800.000 gallons an hour. This arrangement is the least expensive that can be adopted for land drainage or irrigation ; it was suggested by a Dutch engineer who had erected similar works in Java, and has been found in every way satisfactory. The embankment is cut through, and a strong timber bulkhead, A, is erected across the gap. The pumps, P P, are placed immediately behind the bulkhead, with their discharge nozzles projecting through it. Flap valves opening out ward are hung over the discharge nozzles at D, to prevent back-flow through the pumps when not working ; in dry seasons they are sometimes opened for letting water flow through for irrigation. The vertical pump spindles are driven by bevel gearing from a horizontal shaft. The engine, E, is single acting, with two cylinders of 10 in. diameter, and its speed is 300 revolutions per minute. The machinery shown in Fig. 10 was erected during 1885, on the Sacramento River, 75 miles from San Francisco, for draining tule lands.
The average head in this case being onlv from 3 to 5 ft„ it was considered that the water could be driven more by direct push than by centrifugal force. The pumps were constructed accordingly with smooth iron vanes, bolted to a square extension on the pump spindle, as shown in Fig. 11. The throats of the suction inlets were made very sharp, and brought in as close as possible to the inner tips of the vanes. In the writer's . opinion the effect would have been much the same, or, per haps, even better, if the volute casing had been replaced by t h e ordinary concentric easing. When a good tur bine water-wheel will realize a duty of 70 t o 80 percent. by the direct pressure of the water, there seems no reason why a centrifugal pump, considered as a turbine-wheel, acting in the reverse manner, should not utilize, in some near proportion, the power applied to it for moving and raising water. The writer is not aware whether any investigations have been made in this direction ; but there appears to him to be a close analogy be tween the two cases, at least for low heads.
The Lawrence Cen trifugal Pump.—Figs. 12 and 13 show a cen trifugal pump built by the Lawrence Machine Works, Lawrence, Mass. The base and shaft sup ports are cast separate. The latter being bolted to the base, enables one to remove the pulley or babbitt the boxes without disturbing the other parts of the pump. Larger sizes are constructed with two covers, so that the relative position of suction and discharge can be easily changed. by removing the bolts that hold cover to volute and turning the latter around as many bolt holes as desired ; or may be changed from a right to a left hand pump, or vice versa, by turning the volute face about, and, of course, the disk changed about on the shaft also to correspond. A test made in 1690 by 141r. George II. Barrus of a 24-in. Law rence centrifugal pump in .:%lontreal gave a result of percent. efficiency.