Fig. 209 exhibits two _single acting plunger pumps_ actuated by one shaft having a crank upon each end with crank pins opposite to one another. This shaft is supported on the top of two pillars which form a part of the solid cast iron frame. The boxes are babbited. The crank shaft has a cast iron spur gear keyed to it and meshes into a pinion upon the pulley shaft. The teeth are cut to insure smooth and quiet running. The power is transmitted through a belt upon a tight and loose pulley. Each pump is secured to the frame by four bolts. The lower end of the pitman has an arrangement to take up the wear by means of two set screws with lock-nuts as shown in the figure on the top of each plunger. This pump is largely used as a boiler feed pump. These pumps can be used separately or together and with single or compound connections. _Duplex Power Pump._ This engraving, Fig. 210, shows a special boiler feed pump having ball valves, as shown in section, and which is also intended for use in pulp mills and in other places where it is necessary to pump sandy or muddy water, or chemicals, soap and other heavy bodied liquids. These pumps have composition ball valves, composition plungers and composition lined cylinders and glands. The two barrels or cylinders of this pump are brought together so as to occupy as little space as possible. Instead of cranks eccentrics are used having very large wearing surfaces. Each pitman has a ball at its lower extremity forming a “ball and socket” joint, which is adjustable to compensate for wear. All the bearings are Babbitted and like the last pump described the gears have cut teeth. It is belt driven. _If there are two cranks as in the duplex power pump_ they are placed opposite to one another or 180° apart, the circle described by the crank-pin containing 360 degrees. _In the triplex pump_ this circle is divided into three equal parts of 120° each which is represented by the position of the cranks; _a quadruplex_ or two duplex pumps attached to the same shaft the cranks will be 90° apart. This arrangement effects a uniform distribution of load on the crank shaft and one of the pumps is continuously discharging at its maximum capacity. This duplex _power_ pump should not be confounded with the “Duplex Pump” so called. The latter has two steam cylinders and two water cylinders and is double acting while the former is single acting. The successful operation and durability of these, as of all power pumps, depends largely upon the judicious selection and application of a proper _packing to the stuffing boxes_. As for example, plaited flax dipped in a mixture of warm graphite and tallow, braided rawhide, Selden’s packing, etc., have proved by long service to have a _low co-efficient of friction_ and are not liable to cut the plungers.