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.
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