If you wish to fit a force pump it should be placed centrally between the cylinders and be worked by an eccentric on the main shaft, but a pump on a model locomotive is next to useless unless it is also made to work by hand.
In Fig. 29, we have one which can be worked either way. A is the pump; B the eccentric on main-shaft to work it by steam power. To work by hand you have only to push up hook connection C, which disconnects it from the eccentric; and then by working the handle D, which is screwed into the bottom of the plunger C, the water is forced into the boiler. An extra stuffing-box at F will be required. G is the exhaust water pipe bent up to the back-pressure valve on boiler, and H the supply pipe carried on to rear of engine.
Two small blow-off cocks will be necessary on each cylinder to get rid of the condensed steam when starting. They can be connected with a tye-rod, and both worked from the foot-plate with a single handle. Now paint to suit your taste and put away to dry.
Next comes the boiler, which will need extreme care. For this you will require sheet copper an eighth of an inch thick.
First cut a piece 19 inches long by 16 wide and bend it round, forming a cylinder 5 inches in diameter. The cap must be closely riveted and the two ends hammered out into a flange outward, leaving the body of the boiler 17 inches long, as in Fig. 30. B is the shape of the piece to be next riveted on at after end. Now take another sheet 9 inches wide and hammer a half inch flange round it, so as to fit over the dotted line at A. Rivet them firmly together and also another piece in after end. It will then have the appearance of Fig. 31, and should be 4-1/2 inches deep from A to B, and forming a copper box 6 inches wide from B to C and 8 inches from C to D. Then rivet together another box to form the inner casing 4-1/2 inches wide by 6-1/2 inches long and 9 inches deep, the bottom to be hammered outward to the dimensions of B C C D, as shown in section Fig. 32 at A A. A hole is next to be cut out in the center of rear plate and also the rear part of inner casing which comes opposite to it, and 1-3/4 inches by 2-1/2 forming the furnace door.
A casting of that shape and 3/4 of an inch thick, which is the distance between the inner and outer casing B C, must be procured and drilled with holes every 3/8 of an inch and firmly riveted in position, as shown in Fig. 32 at D. Two pins should project on either side of the inner surface to support the fire-bars and ash pan, and the bars should be made of cast iron and small enough to get out easily by tilting up one side; they should run lengthwise of the engine.