Every steam boiler which has to run for long periods and evaporate considerable quantities of water should be in connection with a pump capable of forcing water in against the highest pressure used.  On a previous page (p. 158) we have described a force pump driven directly off the crank shaft of an engine.  As the action of this is dependent on the running of the engine, it is advisable, in cases where the boiler may have to work an engine not provided with a pump of its own, to install an independent auxiliary pump operated by hand or by steam, and of considerable capacity, so that in an emergency water may be supplied quickly.

[Illustration:  Fig. l09.-Vertical section of force pump.]

Making a Hand pump.—­Fig. 109 shows the details of a hand pump which is easy to make.  The barrel is a length of brass tubing; the plunger a piece of brass or preferably gun-metal rod, which fits the tube closely, but works easily in it.  The gland at the top of the barrel, E, is composed of a piece, D, of the same tubing as the barrel, sliding in a collar, C, soldered to E. The bottom of D and top of E are bevelled to force the packing against the plunger.  The plates A and B, soldered to D and C respectively, are drawn together by three or more screws.  A brass door-knob makes a convenient top for the plunger.  When the knob touches A, the bottom of the plunger must not come lower than the top of the delivery pipe, lest the water flow should be impeded and the valve, V, injured.  Round off the end of the plunger, so that it may be replaced easily and without disarranging the packing if pulled out of the pump.

The valves are gun-metal balls, for which seats have been prepared by hammering in steel cycle balls of the same size.  Be careful to select balls considerably larger than the bore of the pipes on which they rest, to avoid all possibility of jamming.  An eighth of an inch or so above the ball, cross wires should be soldered in to prevent the ball rising too far from its seat.

[Illustration:  Fig. 110.]

A convenient mounting for a hand pump is shown in Fig. 110.  The plate, F, of the pump is screwed to a wooden base resting on a framework of bent sheet zinc, which is attached to the bottom of a zinc water tray.  The delivery pipe, G, will be protected against undue strains if secured by a strap to the side of the wooden base.

The same pump is easily adapted to be worked by a lever, which makes the work of pumping easier.  Fig. 111 gives details of the top of the plunger and the links, B. A slot must be cut in the plunger for the lever, A, to pass through, and the sides bored for a pivot pin.  The links are straddled (see sketch of end view) to prevent the back end of the lever wobbling from side to side.

[Illustration:  Fig. 111.—­Details of lever for force pump.]

A Steam Pump.—­The pump illustrated in Fig. 112 belongs to what is probably the simplest self-contained type, as no fly wheel, crank, or eccentric is needed for operating the valve.