Bulletin 947070-B
THE OILGEAR COMPANY
11
PRINCIPLE OF OPERATION
Figure 2. Cut-a-way of a Typical “PVM”
Pump (01010)
Full Stroke Operation - Figure 3
Numbers in parentheses represent item
number in parts list and drawings.
The control piston (19) positions the control pin
(31) and pump swashblock (29) so the pump will
deliver maximum volume to raise pressure in the
system.
Raising Pressure
Pump delivery (and resultant pressure) is fed to
both sides of the control piston (19). Pressure to
the unloading side (C) of the control piston is
direct. Pressure to the bias side (D) of the control
piston is maintained by the respective control.
Note that the flow through the PC control cartridge
(3-1) is blocked.
The areas on either end of the control piston are
the same and the pressure acting on either end is
the same. The resultant hydraulic forces on the
ends of the control piston cancel each other out
(the control piston is balanced), and the force of the
control piston spring (20) controls the control piston
position (19).
Rotating the driveshaft turns the splined cylinder
(38), which contains the pumping pistons (39).
When the cylinder rotates, the pistons move in and
out within their bores as the shoes ride against the
angled swashblock (29).
As the cylinder rotates, the individual piston bores
are connected, alternately, to the crescent shaped
upper (P) and lower (S) in the valve plate. While
connected to the lower side (suction) S, each
piston moves outward OUT, drawing fluid from S
into the piston bore until its outermost stroke is
reached. At this point, the piston bore passes from
the lower crescent S to the upper crescent P.
While rotating across the upper crescent port, each
piston moves across the angled swashblock face
and then each piston is forced inward IN. Each
piston then displaces fluid through the upper
crescent to P until its innermost stroke is reached.
At this point, the piston bore passes from the upper
to the lower crescent again and the cycle is
repeated.
The angle of the swashblock determines the length
of the piston stroke, (the difference between
outermost and innermost position) which
determines the amount of delivery from the pump.
If the stroke angle is one-half of the stroke, the
piston stroke is one-half and the pump delivery is
one-half.
OILG0020
NOTE