_The vacuum pump_ shown in the engraving, Fig. 346, represents a single
cylinder double acting vertical design having but one set of valves and
those used exclusively for the discharge.
The suction port is in the middle of the cylinder, A, shown in the
sectional view, Fig. 347. The piston, E, when it passes this port
imprisons the water beyond it and pushes this water out of the
discharge valves, D D, if the piston is rising, and out of the valves,
C C, if the piston is descending. The main discharge pipe is attached
to a flange at B.
This pump is made to work easily and steadily by adjusting the
cushioning valves, F. F.
The discharge valves are reached through the holes provided for that
purpose and covered by plates shown in the engraving, Fig. 347.
The main slide valve moves horizontally for the reason that if it moved
up and down the force of gravity would seriously interfere with its
regular action.
This slide is moved by a valve piston in the usual way. The parts of
the valve may be inspected and adjusted by removing the cover held by
the two studs shown.
The outline engraving, Fig. 348, shows a cross-compound double acting
vacuum pump, six-inch high pressure, nine-inch low pressure cylinders,
by eight-inch stroke, and two air cylinders, ten-inch diameter by
eight-inch stroke.
They are piped up to run either high or low pressure, also to run
independently by manipulating the cocks, C, and D, _as directed in the
engraving showing arrangement of valves_, Fig. 349, page 41.
[Illustration: FIG. 346.]
These pipes are simple in design and run direct to the boiler for live
steam and convey the exhaust to the atmosphere or condenser as desired.
On a recent test at a fair rate of speed the capacity of this pump was
shown to be equivalent to taking care of a triple expansion engine of
2,000 I. H. P. On a further test this same pump on a basis of 20 lbs.
weight of steam per I. H. P. per hour demonstrated its ability to take
care of 3,000 I. H. P. triple expansion engine.
The advantages claimed for this pump are briefly as follows:
Unusual light weight and compactness.
There being NO SUCTION VALVES, working-beams, rock shaft and bearings,
beam-links, etc., this pump is simple.
It is economical in the use of steam, by reason of compounding the
steam cylinders; also clearance loss is reduced to a minimum by the
perfect regulation that is secured by the valve gear described. Full
stroke at any and all speeds can be readily maintained.
As the air pistons travel within a distance of less than 1/8 inch
of the air cylinder heads, a high efficiency results. Although
double-acting, the flow of water and vapors is always in one continuous
direction—the same as in a single-acting air pump. Either side of pump
can run independent of the other, which means a spare pump to be used
in case of accident to the other side of this pump.
[Illustration: FIG. 347.]
[Illustration: FIG. 348.]
Referring to the accompanying table of tests, page 41, it may be
claimed that with an average of 36 double strokes per minute this pump
handled at the rate of upwards of 26,000 pounds of feed-water per
hour, which on a basis of 20 lbs. engine economy shows this vacuum
pump capable of taking care of a 1,300 I. H. P. engine at this very
moderate speed. By comparing the power required to drive this pump
(which aggregated 1.18 I. H. P.) to the I. H. P. of an engine of the
power here represented it is apparent that this pump did its work on
less than one-eleventh of one per cent. of the I. H. P. of said engine,
which is a very excellent showing.
[Illustration: FIG. 349.—See page 38.]
Table No. 4 also shows a very excellent vacuum maintained under extreme
duty.