The Pump.—­Fig. 65 shows in section the pump, which will be found a useful addition to the engine. (For other details, see Figs. 53 and 54.) Its stroke is only that of the eccentric, and as the water passages and valves are of good size, it will work efficiently at high speed.  The method of making it will be obvious from the diagrams, and space will therefore not be devoted to a detailed description.  The valve balls should, of course, be of gun-metal or brass, and the seatings must be prepared for them by hammering in a steel ball of the same size.

In practice it is advisable to keep the pump always working, and to regulate the delivery to the boiler by means of a by-pass tap on the feed pipe, through which all or some of the water may be returned direct to the tank.

The tank, which should be of zinc, may conveniently be placed under the engine.  If the exhaust steam pipe be made to traverse the tank along or near the bottom, a good deal of what would otherwise be wasted heat will be saved by warming the feed water.

Making a Governor.

[Illustration:  Fig. 66.—­Elevation of governor for horizontal engine.  Above is plan of valve and rod gear.]

It is a great advantage to have the engine automatically governed, so that it may run at a fairly constant speed under varying loads and boiler pressures.  In the absence of a governor one has to be constantly working the throttle; with one fitted, the throttle can be opened up full at the start, and the automatic control relied upon to prevent the engine knocking itself to pieces.

The vertical centrifugal apparatus shown in Fig. 66 was made by the writer, and acted very well.  The only objection to it is its displacement of the pump from the bed.  But a little ingenuity will enable the pump to be driven off the fly wheel end of the crank shaft, or, if the shaft is cut off pretty flush with the pulley, off a pin in the face of the pulley.

Turning to Fig. 66, A is a steel spindle fixed in a base, L, screwed to the bed.  B is a brass tube fitting A closely, and resting at the bottom on a 1/4-inch piece of similar tubing pinned to A.

A wooden pulley jammed on B transmits the drive from a belt which passes at its other end round a similar, but slightly larger, pulley on the crank shaft.  This pulley is accommodated by moving the eccentric slightly nearer the crank and shortening the fly-wheel side bearing a little.

The piece G, fixed to B by a lock screw, has two slots cut in it to take the upper ends of the weight links DD; and C, which slides up and down B, is similarly slotted for the links Ee.  Each of the last is made of two similarly shaped plates of thin brass, soldered together for half their length, but separated 3/32 inch at the top to embrace the projections of D. To prevent C revolving relatively to B, a notch is filed in one side of the central hole, to engage with a piece of brass wire soldered on B (shown solid black in the diagram).  A spiral steel spring, indicated in section by a number of black dots, presses at the top against the adjustable collar F, and at the bottom against C.