Hydraulic Balance; Wafer Plate Operation - Eaton Vickers VMQ125S Series Service Manual

Section III —
Principles of
Operation (cont.)
C. Hydraulic Balance
D. Wafer Plate Operation
Outlet Port
Inlet Port
Wafer Plates
Under Vane Pin
Internal Rotor Cavity
Rotor Terminal Hole
EATON Vickers Single, Double, Triple and Thru-drive Pumps Overhaul Service Manual V-PUVN-TS001-E October 2002
Figure 4. VMQ Wafer Plate, Rotor and Vanes
The pump ring is shaped so
the two pumping chambers are
formed 180 degrees apart
(Figure 3). Thus, opposing
The main function of the
wafer plates is to control the
pressure timing of the pump.
Machined cavities in the wafer
plates distribute high pressure
from the outlet ports to the
terminal holes in the rotor.
These cavities also feed high
pressure through the rotor to
the pins behind the vanes.
With high pressure distributed
through the rotor and applied
to the under vane pins, the
forces between the vane tip
and cam are regulated. Finally,
metering grooves in the plates
are positioned in such a way to
reduce excess cavitation, thus

Wafer Plate Operation

Figure 5.
Inlet Window
Vane Cross Section
Pressure Balance Holes in Vane
Under Vane Pin
Rotor Terminal Hole
Rotor Bushing
Wafer Plate
Outlet Window
Rotor
hydraulic forces which
develop side loads on the
shaft cancel out.
limiting the overall sound level
of the pump. The position of
the wafer plates in the
cartridge kit can be seen in
Figure 5.
VMQ wafer plates have a
bronze finish that rides next to
the rotor and provides excellent
wear and thermal shock
characteristics.
The inlet and outlet support
plates hold the wafer plates in
position and contain passages
which allow fluid to pass from
the inlet port to the pumping
cartridge and from the
cartridge to the outlet port.
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