Figure 12-17.--Mechanical drive.
Figure 12-19.--Pressure control mechanism.
check spring pressure closes the check spring when
During normal pump operation, three conditions
piston bypass ports align with the cylinder block
may exist--full flow, partial flow, and zero or nonflow.
bypass passage. The partial vacuum occurring in the
During full flow operation (fig. 12-20), fluid enters the
cylinder during the piston return causes reservoir fluid
intake port and is discharged to the high-pressure side
to flow from the intake loading groove into the
past the pump checks by the reciprocating action of the
pistons. Piston sleeves cover the relief holes for the
Pressure Control.--A schematic diagram of the
entire pressure stroke.
pressure control mechanism is shown in figure 12-19.
During partial flow, system pressure is sufficient
Pressure is bled through the control orifice into the
(as bled through the orifice) to move the compensator
pressure compensator cylinder, where it moves the
stem against the compensator spring force.
compensator piston against the force of the calibrated
control (compensator) spring. This motion,
If system pressure continues to build up, as under
transmitted by a direct mechanical linkage, moves
nonflow conditions, the stem will be moved further
sleeves axially on the piston, thereby varying the time
until the relief holes are uncovered for practically the
during which relief holes are covered during each
entire piston stroke. Relief holes will be covered only
for the stroke necessary to maintain pressure against
Fluid flows through the hollow pistons during the
system leakage and to produce adequate bypass flow.
forward stroke and escapes out the relief holes until
Bypass.--The bypass system is provided to
they are covered by the piston sleeves. The effective
supply self-lubrication, particularly when the pump is
piston stroke (delivery) is controlled by the piston
in nonflow operation. The ring of bypass holes in the
sleeve position. During nonflow requirements, only
pistons are aligned with the bypass passage each time a
enough fluid is pumped to maintain system pressure
piston reaches the very end of its forward travel. This
pumps a small quantity of fluid out the bypass passage,
back to the supply reservoir, and provides a constant
changing of the fluid in the pump. The bypass is
designed to pump against a considerable back pressure
for use with pressurized reservoirs.
Maintenance.--Line maintenance of the
Stratopower pump is limited to operational checks, and
checking for leaks and loose fittings. Malfunctioning
pumps should be removed and replaced.
In removing a pump, always maintain its
alignment until the drive shaft is fully withdrawn from
the driving element. Never pick up or carry a pump by
the drive shaft extension.
Figure 12-18.--Fluid displacement.