The details of the valve gear used on the Deane single cylinder steam
pumps are shown in the accompanying engraving. The main valve is
operated by a small piston called the valve piston, shown in Fig. 286.
The ears on the main valve fit freely but without lost motion into a
slot cut in the valve piston, so that when the valve piston moves in
either direction it carries the main valve with it.
The valve piston is fitted to the valve chest and is operated by steam
admitted alternately to the opposite ends of the chest. The movements
of this valve piston are controlled by a secondary valve, which admits
and exhausts the steam to the valve piston through the small ports at
the sides of the steam chest. The secondary valve derives its motion
from the valve stem, tappets, links and the piston rod as shown.
The valve piston is steam jacketed which insures equal expansion of the
parts in starting the pump and prevents the seats from pinching the
valve piston before these parts have acquired a uniform temperature.
The action of this pump is as follows: Suppose the piston moving in the
direction of the arrow nears the end of the stroke; the tappet block
comes in contact with the left-hand tappet and throws the secondary
valve to the left until it’s edge, A, Fig. 284, uncovers the small
port, S, Fig. 283, admitting steam to the valve piston.
The port, E, and chamber, F, in the secondary valve provide for
the exhaust of steam from the left-hand end of valve piston in the
same manner and at the same time that steam is admitted behind the
right-hand end. The exhaust ports in the chest allow for properly
cushioning the valve piston. The small ports on the other side of the
steam cylinder, Fig. 283, control the motion of the valve in the other
direction and act in exactly the same manner as those just described.
In case the steam pressure should for any reason fail to start the
valve piston in time there is a lug, B, Fig. 286, which forms a part
of the valve stem and comes in contact with the valve piston and the
entire power of the steam cylinder starts it. The correct timing of the
valve movements is controlled by the position of the tappets. If they
are too near together, the valve will be thrown too soon and thus the
stroke of the pump will be shortened, while on the other hand if too
far apart, the pump will complete its stroke without moving the valves.
The tappets are set and keyed securely before leaving the factory.
[Illustration: FIGS. 283-285.]
[Illustration: FIG. 286.]
The exhaust from the cylinder is cut off when the piston covers the
inner port, and forms a steam cushion for the piston to prevent it
striking the heads.
_To set the valve._ Place the steam piston at the end of stroke nearest
stuffing-box and the secondary valve so that it will uncover the steam
port, S, Fig. 283. Set the tappet next to the steam cylinder on the
valve stem against the tappet block and secure it in this position.
Slide the secondary valve forward until the opposite steam port is
uncovered and place the steam piston in its extreme outward position,
then set the other tappet against the tappet block. Now set the valve
so that the inside main steam port is open and the valve piston in
position to engage the main steam valve, put the valve chest on the
cylinder and secure it in place. The pump will then be ready to start
on the admission of steam to the steam chest.
If when steam is turned on the pump refuses to start, simply move the
valve rod by hand to the end of its stroke and the pump will move
without trouble.
In renewing the packing between the steam chest and cylinder extreme
caution should be observed to cut out openings for the small ports.