[Illustration: FIG. 270.]
This pump is for deep wells; it has a valve piston and two slide valves
operated by valve stem, also supplemental port valves to regulate
and control the up and down strokes of the main piston. The main and
auxiliary valves are both flat slides, each covering five ports, as
shown in Fig. 271. The main valve is actuated by means of a valve
piston, the steam being admitted to and exhausted from the ends of the
valve piston in precisely the same manner that the main valve controls
the admission and release of steam in the main pump cylinder.
[Illustration: FIG. 271.]
One of the auxiliary ports enters the end of the main steam chest, and
the other enters at a point nearer the middle of the chest. The end
ports are admission only and the inner ones exhaust. When the auxiliary
valve reaches the upper end of its travel, as shown in the engraving,
the admission port opens at the bottom of the steam chest, while the
one at the top closes.
At the same time, the upper end of the main cylinder is open to the
exhaust. The admission of steam drives the valve piston upward, but
before reaching the end of its stroke it closes the exhaust port, thus
entrapping a portion of the exhaust steam, which cushions the valve
piston at the ends of the stroke.
The auxiliary slide valve is operated by means of a double-cone tappet
on the piston rod, which strikes a rocker bar pivoted to the frame of
the pump. The rocker bar carries an arm or lever at right angles to it
and to this arm the valve rod is connected.
A short shaft runs across and through the upper part of the steam chest
and is provided with a toe, as shown, by means of which the valve
piston may be moved by hand when necessary and without disconnecting
any part of the pump or valve gear.
[Illustration: FIG. 272.]
The port valves provide a simple means of contracting these passages
and regulating the velocity of the up and down strokes to meet the
requirements of the water ends of the pump so that uniform strokes are
obtained regardless of the resistance against the main piston.
When adjusting the auxiliary valve, place the rocker bar parallel to
the piston rod and so that the arm to which the valve rod is connected
will stand at right angles to the piston rod. The auxiliary valve must
then cover all the ports equally. The upper or outer end of the arm on
the rocker bar is slotted, hence moving the valve rod pin toward the
end of the arm lengthens the stroke and moving it toward the piston rod
shortens it.
_To set the valve_ of this pump it is necessary only to square the
levers and equalize the travel.