The valve motion can then be taken in hand.  Cut off for the guides, G1 G2, two pieces of stout brass strip, 2-1/2 inches long and 3/4 inch wide.  Lay them together in a vice, and bore the holes (Fig. 113) 1-1/4 inches apart, centre to centre, for the 1/8-inch rods, R1 R2.  The feet are then turned over and a third hole bored in G1, midway between those previously made, to take the end of the support, pp, of the rocking lever.

[Illustration:  Fig. 113.—­End view of striking mechanism of steam pump.]

Screw G1 G2 down to the bedplate, 3/4 inch away from the cylinder centre line.  G1 is abreast of the mouth of the pump, G2 about half an inch forward of the end of the cylinder.

The striker, S, is a piece of brass strip soldered to 1/2 inch of tubing fitting the piston rod. (See Fig. 113.) Its length is decided by running a rod through the upper holes in G1 G2, allowance being made for the notch in the end.  The collar is tapped for two screws, which prevent S slipping on the piston rod.  The rods for R1 R2 are now provided with forks, made by cutting and filing notches in bits of brass tubing.  The notches should be half as deep again as the rocking lever is wide, to give plenty of room for movement.  Solder the forks to the rods, and put the rods in place in the guides, with the forks as far away from G1 as the travel of the slide valve.  Then measure to get the length of the rocking lever support.  One end of this should be filed or turned down to fit the hole drilled for it; the other should be slotted to fit the lever accurately.

The rocking lever, RL, which should be of steel, is slotted at each end to slide on the pins in the forks, and bored for the pivot pin, which, like those in the forks, should be of hardened steel wire.  Assemble the rocking lever in its support and the rod forks, and solder on the support.

To the back end of R2 solder a steel plate, A, which must be bored for the pin in the valve fork, after the correct position has been ascertained by careful measurement.

The stops, T1 T2, are small, adjustable collars, kept tightly in place on R1 by screws.

Setting the Striker.—­Assemble all the parts.  Pull out the piston rod as far as it will go, and push the slide valve right back.  Loosen the striker and the forward stop, and slide them along in contact until the striker is close to the pump.  Tighten up their screws.  Then push the piston rod fully in, draw the valve rod fully out, and bring the rear stop up against the striker, and make it fast.  Each stop may now be moved 1/16 inch nearer to a point halfway between them to cause “cushioning” of the piston, by admitting steam before the stroke is quite finished.

A pump made by the author on this principle, having a 1-1/4 inch stroke and a 1/2-inch bore, will deliver water at the rate of half a gallon per minute against a head of a few feet.

Note.—­To steady the flow and prevent “water hammer,” a small air-chamber should be attached to the delivery pipe.