The cylinder will not be described in detail, as hints on making a
slide-valve cylinder have been given on earlier pages. The piston rod
should be three times as long as the stroke of the cylinder, if it is
to serve as pump plunger; and near the pump end an annular groove must
be sunk to take a packing.
The pump, if designed to work horizontally, will have the valves
arranged like the pump illustrated in Fig. 65; if vertically, like the
pump shown in Fig. 109. Both suction and delivery pipes should be of
ample size, as the pump works very fast. The pump is mounted on a foot,
F, made by turning up the ends of a piece of brass strip, and filing
them to fit the barrel.
The bed can be fashioned out of stout sheet brass or zinc. Let it be of
ample size to start with, and do not cut it down until the pump is
complete. Rule a centre line for cylinder and pump, and mount the
cylinder. Pull out the piston rod plunger as far as it will go, and
slip the pump barrel on it. The foot of the pump must then be brought
to the correct height by filing and spreading the ends until the
plunger works quite easily in the pump, when this is pressed down
firmly against the bed. When adjustment is satisfactory, mark the
position of the foot on the bed, solder foot to barrel, and drill and
tap the foot for the holding-down screws. Don’t forget that the
distance between pump and cylinder gland must be at least 1-1/3 times
the stroke.
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.
An Alternative Arrangement.—If the reader prefers a steam pump which
will work at slow speeds, and be available, when not pumping, for
driving purposes, the design may be modified as shown diagrammatically
in Fig. 114. The striker becomes a cross head, and is connected by a
forked rod passing on each side of the pump with the crank of a fly
wheel overhanging the base. The valve is operated in the ordinary
manner by an eccentric on the crankshaft. The steadying effect of the
fly wheel and the positive action of the valve make it possible to use
a larger pump plunger than is advisable with the striking gear. With a
pump piston of considerably greater diameter than the piston rod, the
pump may be made double-acting, a gland being fitted at the front end
for the piston rod to work through, and, of course, a second set of
valves added.
[Illustration: Fig. 114.—Plan of steam pump with fly wheel.]