If you want to be a successful engineer it is necessary to know all
about the pump. I have no doubt that many who read this book, cannot
tell why the old wooden pump (from which he has pumped water ever since
he was tall enough to reach the handle) will pump water simply because
he works the handle up and down. If you don't know this I have quite a
task on my hands, for you must not attempt to run an engine until you
know the principle of the pump. If you do understand the old town pump,
I will not have much trouble with you, for while there is no old style
wooden pump used on the engine, the same principles are used in the
cross head pump. Do not imagine that a cross head pump means something
to be dreaded. It is only a simple lift and force pump, driven from the
cross head. That is where it gets its name and it don't mean that you
are to get cross at it if it don't work, for nine times out of ten the
fault will be yours. Now I am well aware that all engines do not have
cross head pumps and with all respect to the builders of engines who do
not use them, I am inclined to think that all standard farm engines
ought to have a cross head pump, because it is the most simple and is
the most economical, and if properly constructed, is the most reliable.
A cross head pump consists of a pump barrel, a plunger, one vertical
check valve and two horizontal check valves, a globe valve and one stop
cock, with more or less piping. We will now locate each of these parts
and will then note the part that each performs in the process of feeding
the boiler.
You will find all, or most pump barrels, located under the cylinder of
the engine. It is placed here for several reasons. It is out of the
way. It is a convenient place from which to connect it to the cross
head by which it is driven. On some engines it is located on the top or
at the side of the cylinder and will work equally well. The plunger is
connected with the cross head and in direct line with the pump barrel,
and plays back and forth in the barrel. The vertical check valve is
placed between the pump and the water supply. It is not absolutely
necessary that the first check be a vertical one, but a check of some
kind must be so placed. As the water is lifted up to the boiler it is
more convenient to use a vertical check at this point. Just ahead and a
few inches from the pump barrel is a horizontal check valve. Following
the course of the water toward the point where it enters the boiler, you
will find another check valve. This is called a "hot water check." just
below this check, or between it and where the water enters the boiler,
you will find a stop cock or it may be a globe valve. They both answer
the same purpose. I will tell you further on why a stop cock is
preferable to a globe valve. While the cross head pumps may differ as
to location and arrangement, you will find that they all require the
parts described and that the checks are so placed that they bear the
same relation to each other. No fewer parts can be used in a pump
required to lift water and force it against steam pressure. More check
valves may be used, but it would not do to use less. Each has its work
to do, and the failure of one defeats all the others. The pump barrel
is a hollow cylinder, the chamber being large enough to admit the
plunger which varies in size from 5/8 of an inch to I inch in diameter,
depending upon the size of the boiler to be supplied. The barrel is
usually a few inches longer than the stroke of the engine, and is
provided at the cross head end with a stuffing box and nut. At the
discharge end it is tapped out to admit of piping to conduct water from
the pump. At the same end and at the extreme end of the travel of the
plunger it is tapped for a second pipe through which the water from the
supply reaches the pump barrel. The plunger is usually made of steel and
turned down to fit snug in the chamber, and is long enough to play the
full stroke of engine between the stuffing box and point of supply and
to connect with the driver on the cross head. Now, we will take it for
granted, that, to begin with, the pump is in good order, and we will
start it up stroke at a time and watch its work. Now, if everything be
in good order, we should have good water and a good hard rubber suction
hose attached to the supply pipe just under the globe valve. When we
start the pump we must open the little pet cock between the two
horizontal check valves. The globe valve must be open so as to let the
water in. A check valve, whether it is vertical or horizontal, will
allow water to pass through it one way only, if it is in good working
order. If the water will pass through both ways, it is of no account.
Now, the engine starts on the outward stroke and draws the-plunger out
of the chamber. This leaves a space in the barrel which must be filled.
Air cannot get into it, because the pump is in perfect order, neither
can the air get to it through the hose, as it is in the water, so that
the pressure on the outside of the water causes it to flow up through
the pipes through the first check valve and into the pump barrel, and
fills the space, and if the engine has a I2-inch stroke, and the plunger
is I inch in diameter, we have a column of water in the pump I2 inches
long and I inch in diameter.
The engine has now reached its outward stroke and starts back. The
plunger comes back with it and takes the space occupied by the water,
which must get out of the way for the plunger. The water came up
through the first check valve, but it can't get back that way as we have
stated. There is another check valve just ahead, and as the plunger
travels back it drives the water through this second check. When the
plunger reaches the end of the backward stroke, it has driven the water
all out. It then starts forward again, but the water which has been
driven through the second check cannot get back and this space must
again be filled from supply, and the plunger continues to force more
water through the second check, taking four or five strokes of the
plunger to fill the pipes between the second check valve and the hot
water check valve. If the gauge shows I00 pounds of steam, the hot
water check is held shut by I00 pounds pressure, and when the space
between the check valves is filled with water, the next stroke of the
plunger will force the water through the hot water check valve, which is
held shut by the I00 pounds steam pressure so that the pump must force
the water against this hot water check valve with a power greater than
I00 pounds pressure. If the pump is in good condition, the plunger does
its work and the water is forced through into the boiler.
A clear sharp click of the valves at each stroke of the plunger is
certain evidence that the pump is working well.
The small drain cock between the horizontal checks is placed there to
assist in starting the pump, to tell when the pump is working and to
drain the water off to prevent freezing. When the pump is started to
work and this drain cock is opened, and the hot water in the pipes
drained off, the globe valve is then opened, and after a few strokes of
the plunger, the water will begin to flow out through the drain cock,
which is then closed, and you may be reasonably certain that the pump is
working all right. If at any time you are in doubt as to whether the
pump is forcing the water through the pipes, you can easily ascertain by
opening this drain cock. It will always discharge cold water when the
pump is working. Another way to tell if the pump is working, is by
placing your hand on the first two check valves. If they are cold, the
pump is working all right, but if they are warm, the cold water is not
being forced through them.
A stop cock should be used next to boiler, as you ascertain whether it
is open or shut by merely looking at it, while the globe valve can be
closed by some meddlesome party and you would not discover it, and would
burst some part of your pump by forcing water against it.