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