.84 PUMP of moderate size which are driven by steam are known as direct-acting steam pumps ; that is, there is no intervention of rotary motion, the reciprocating motion not being caused by the action of an eccentric, and the dead points or centres are avoided by the use of what is called an auxiliary valve. A good steam pump of this kind, constructed by the " Knowles Steam Pump Works " of War- ren, Mass., a company owning the patent for the auxiliary valve, is shown in fig. 8. The auxiliary valve, A, moves back and forth with- in the steam chest, and it also has a slight rotary motion by which the ports at each end are opened and shut to produce reciprocating motion. When steam is admitted into the steam chest, it enters the valve A at the mid- dle portion and passes out at one of the ports of the main flat valve v 0, this valve being moved over its seat by the motion of the aux- iliary valve, through the medium of the stem S, which plays in a slot wide enough to admit of the slight rotation of the auxiliary valve. Now, when the steam enters the cylinder C, we will suppose upon the left, the piston is driven in the direction GD. This carries the standard F in the same direction. In the top of this standard there is a hole which slides over the rod d' d", upon which there are two cams, w and o. When the top of the standard strikes one of these, it pushes the rod d' d" which is attached to the auxiliary valve A in one direction, and also rotates it sufficiently to reverse the ports in the steam chest. The main valve v is therefore reversed and steam is ad- mitted upon the other side of the piston head, by which means the standard F is moved in the direction opposite to its previous one, so that it will strike the opposite cam and cause into French mines by Belidor in 1739, and is described in his Architecture hydraulique. It consists of two cylinders, a larger, C, fig. 9, and a smaller, D, with a piston in each, con- nected by a common rod. A supply pipe, A, conveys the descending column from its source FIG. S. Knowles'g Steam Puuip. the rod d' d" to move forward and rotate and again reverse the auxiliary valve A. The pump is simply a double-acting force pump with an air chamber, and its action needs no special explanation. A force pump called a hydraulic pressure engine was devised and introduced Fia. 9. Hydraulic Pressure Engine, from Belldor. to the three-way cock F, the air chamber E and the pipe B being the way of exit for that portion of the water which is raised. When the water from A enters the way leading into 0, the piston in this cylinder, having, we will suppose, twice the area of cross section as the one in I), will force the water from the latter up the pipe B at each stroke until it has twice the elevation of the source supplying A. The three-way cock is so arranged that the pipe A is connected with the cylinder C or with the pipe H, and through it with the cylinder D by means of connections between the piston rod and a set of levers. When the piston in re- turns toward F, an opening at one side of the three-way cock allows the water to escape, the opening being closed when the piston begins to move in the direc- tion of D. A portion of the water therefore runs to waste, a neces- sary result of the laws of mechanics. Rotary Pumps. These are of two kinds, force pumps proper and centrifugal pumps. One of the old- est forms of rotary force pumps of which there is an account was con- tained in a collection of old models by Serviere, born at Lyons in 1598. It consists of two cog wheels within an ellip- tical box, fitting accu- rately, as shown in fig. 10. It will be readily seen that the water must be propelled in the direction taken by the cogs which are in con- tact with the box. The cogs, fitting to each other accurately in the centre of the box, pre- vent the return of water, and the machine
