PUMP 85 becomes both a force and a suction pump. When accurately made and used only in clear water, it is quite an efficient machine, and has since been employed as a form of rotary steam engine. It could not be used to raise water containing gravel or much solid matter. An- Fio. 10. Rotary Pump from Servifere's collection. FIG. 11. Rotary Pump of 16th century. other old form of rotary pump of the 16th cen- tury is shown in fig. 11. A wheel of a diame- ter and thickness proportional to the capacity of the pump has its periphery formed into three cams, which give space for the passage of water between them and the inner surface of the cylindrical box in which it moves, and also raise and drop a broad sliding vertical bar, B (seen edgewise), which acts as a shut-off to the passage of the water within the box, di- recting it into the pipe A. The cams act the part of pistons, the water entering at the bot- tom of the cylinder and being forced in the di- rection of the arrows. To prevent its return on stopping the pump, a lift valve is placed in the discharge pipe, which shuts when the pressure above exceeds that below it. There are many other and recent forms of rotary force pumps, acting much upon the same prin- ciples, with the addition of devices which se- Fi(!. 12 FIG. 13. Bagley and Sewall's Rotary Pump. cure greater efficiency. One of the latest of these is Bagley and Sewall's, patented by L. D. Green, of which fig. 12 is a vertical longitu- dinal, and fig. 13 a transverse section. A is the main case, made in one piece, and having attached the ring B, seen in both sections. The space outside of B is the water space. This cylinder is enclosed by the disk D, which is attached to the shaft. An eccentric ring, E, is attached to the disk D so that in revolving its outer surface touches the inside of the case A, while the interior surface upon the opposite side of the ring touches the outside of the ring B. The eccentric ring E acts as the pis- ton of the pump. The suction and discharge are respectively shown in both sections at I and J, the direction of the water being indica- ted in fig. 12 by the arrows. The parts are sep- arated by the sliding valve H H, which is moved back and forth on its seat by means of two tumblers shown in fig. 13 between H and H. These tumblers are moved by the eccen- tric ring E, which passes between them. The centre ring B is made enough deeper than the casing A, as shown in fig. 12, to equalize the quantity of water within and without the ec- centric piston ring E. F is the cover or outside case, and contains a closed bearing for the end of the shaft. The inner part of the disk D forms a collar G to the shaft, and by means of a screw at the end this collar can be forced tightly against its seat K, thus avoiding the use of packing. In the centre of the seat there is a circular groove, shown in section at K K, which connects by a drilled channel with the suction part. Any tendency to escape of water at the seat by pressure is thus overcome by vacuum force. The chain pump consists of an endless chain carrying cups or disks around two drums, one beneath the surface of the water in the well or stream, and the other at a convenient elevation. The ascending part of the chain passes through a pipe just large enough to allow the cups or disks, which act as pistons, to move with little friction. It will thus be seen that the chain pump is little else FIG. 14. Old French Chain Pump. than a modified form of rotary pump. When the water is to be raised to a moderate height, it often becomes a convenient and useful ma- chine. Fig. 14 shows the form of an old French chain pump used in the ship yards at Mar- seilles, described by Belidor. It was worked
