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Section III – Principles of Operation
A. Pumping Cartridge
As mentioned in Section II, fluid flow is developed by the
pumping cartridge. The action of the cartridge is illustrated in
Figure 2. The rotor is driven within the cam ring by the
driveshaft, which is coupled to a power source. As the rotor
turns, centrifugal force causes the vanes to follow the
elliptical inner surface of the cam ring.
Radial movement of the vanes and turning of the rotor
causes the chamber volume between the vanes to increase
as the vanes pass the inlet sections of the cam ring. This
results in a low pressure condition which allows atmospheric
pressure to force fluid into the chambers. (Fluid outside the
inlet is at atmospheric pressure or higher.)
This fluid is trapped between the vanes and carried past the
large diameter or dwell section of the cam ring. As the outlet
section is approached, the cam ring diameter decreases and
the fluid is forced out into the system. System pressure is fed
under the vanes, assuring their sealing contact against the
cam ring during normal operation.
Cam ring
Vane
Outlet
Rotor
Drive shaft
Inlet
Outlet
Inlet
Inlet
Outlet
Figure 2.
B. Hydraulic Balance
The pump cam ring is shaped so that the two pumping
chambers are formed diametrically opposed. Thus, hydraulic
forces which would impose side loads on the shaft are
cancelled.
C. Pressure Plate
The pressure plate seals the pumping chamber as shown in
Figure 3. A light spring holds the plate against the cartridge
until pressure builds up in the system. System pressure is
effective against the area at the back of the plate, which is
larger than the area exposed to the pumping cartridge. Thus,
an unbalanced force holds the plate against the cartridge,
sealing the cartridge and providing the proper running
clearance for the rotor and vanes.
D. Flow Control and Relief Valve
1. Maximum flow to the operating circuit and maximum
system pressure are determined by the integral flow control
and relief valve in a special outlet cover used on some V200
pumps. This feature is illustrated pictorially in Figure 4. An
orifice in the cover limits maximum flow. A pilot operated type
relief valve shifts to divert excess fluid delivery to tank, thus
limiting the system pressure to a predetermined maximum.
Back
pressure
in system
effective here
Cover
Pressure plate
Pressure in
cartridge
Spring
Shaft
Rotor
Vane
Ring
Discharge
Figure 3.
2. Figure 4A shows the condition when the total pump
delivery can be passed through the orifice. This condition
usually occurs only at low drive speeds. The large spring
chamber is connected to the pressure port through an orifice.
Pressure plus spring load in this chamber slightly exceeds
pressure at the other end of the relief valve spool and the
spool remains closed. Pump delivery is blocked from the
tank port by the spool land.