Kohler K91 Owner's Manual page 294

3.4297.424
The flaws can be corrected by installing a
reservoir and two check valves. One check
valve will keep oil from being forced back into
the reservoir and the second will keep the oil
under the cylinder when the pump handle is
raised.
When the pump arm is raised, the surface area
of the chamber between the check valves
increases. As the area increases, pressure
acting on the surfaces inside the chamber
decreases. When the pressure in the reservoir
becomes greater than the spring pressure on
the check valve and the pressure in the
chamber; the check valve moves off its seat.
As oil flows into the chamber, the pressure
begins to increase. As the handle is pushed
downward, the pressure inside the chamber
increases and closes the check ball under the
reservoir.
The second check ball now opens allowing the
oil to flow into the chamber under the cylinder
ram.
The force needed to extend the cylinder ram is
dependent on the amount of weight on the ram.
A five pound weight requires five pounds of
force to lift. Because the size (area) of the
cylinder can not be changed, adding more
weight to the cylinder requires a higher pressure
to achieve movement.
When the pump reaches the end of its stroke,
pressure under the pump and cylinder
equalizes, allowing the check valve to close and
trapping the oil under the cylinder.
3.4297.425
Productivity Series
18