If it seems necessary, run a
little extra solder along the joint, both sides, and at the ends.
The valve, if built up, consists of a central rod, threaded at the rear
end, four washers which fit the tube, and a central spacing-piece. The
forward washer is soldered to the rod. Behind this is placed a felt
packing. Then come in order the central spacing-piece, with a washer
soldered to each end, a second packing, and a fourth washer. The series is
completed by an adjusting nut to squeeze the packings, and a lock nut to
prevent slipping. The back end of the valve must be wide enough to just
more than cover the steam port. If the felt proves difficult to procure or
fit, one may use a ring or two of brass tubing, with an external packing of
asbestos cord.
The cylinder wing W should have the top edge turned over for an eighth of
an inch or so to give a good bearing against the cylinder, and be held in
position by a wire while the soldering is done. It is important that the
line of the wing should be at right angles to a line passing through the
centres of the valve tube and cylinder.
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