running athwartships at the end of the tubes.

[Illustration: Fig. 58. SAFETY VALVE. Gooch.]

662. _Q._--Of what construction is the safety valve?

_A._--There are two safety valves, consisting of pistons 1-3/16 inch in
diameter, and which are kept down by spiral springs placed immediately over
them. A section of this valve is given in fig. 58.

663. _Q._--What are the dimensions of the feed pumps?

_A._--The feed pumps are of brass, with plungers 4 inches diameter and
3-1/4 inches stroke. The feed pipe is of copper, 2 inches diameter. A good
deal of trouble has been experienced in locomotives from the defective
action of the feed pump, partly caused by the leakage of steam into the
pumps, which prevented the water from entering them, and partly from the
return of a large part of the water through the valves at the return stroke
of the pump, in consequence of the valve lifting too high. The pet cock--a
small cock communicating with the interior of the pump--will allow any
steam to escape which gains admission, and the air which enters by the cock
cools down the barrel of the pump, so that in a short time it will be in a
condition to draw. The most ordinary species of valve in the feed pumps of
locomotives, is the ball valve.

Notwithstanding the excellent performance of the best examples of
locomotive engines, it is quite certain that there is still much room for
improvement; and indeed various sources of economy are at present visible,
which, if properly developed, would materially reduce the expense of the
locomotive power. In all engines the great source of expense is the fuel;
and although the consumption of fuel has been greatly reduced within the
last ten or fifteen years, it is capable of being still further reduced by
certain easy expedients of improvement, which therefore it is important
should be universally applied. One of these expedients consists in heating
the feed water by the waste steam; and the feed water should in every case
be sent into the boiler _boiling hot_, instead of being quite cold, as is
at present generally the case. The ports of the cylinders should be as
large as possible; the expansion of the steam should be carried to a
greater extent; and in the case of engines with outside cylinders, the
waste steam should circulate entirely round the cylinders before escaping
by the blast pipe. The escape of heat from the boiler should be more
carefully prevented; and the engine should be balance