Page 147 - Fluid Power Engineering

Hydraulic Pumps 121

S…Suction P…Pressure

(a) (b)

P
P

S P

(c) (d)
FIGURE 4.34 Pressurization of vains’ roots and intra vane.

or the suction lines. The four grooves are arranged on a circle, facing
the pressurizing grooves (4). The vane has four main positions:

• The vane separates two chambers in connection with the
suction line. Both the vane root and the intra-vane chamber
are not pressurized and the vane is pressure balanced (see
Fig. 4.34a).
• The vane separates two chambers in connection with the
pressure line, Fig. 4.34b. At this position, the vane root and
intra vane are pressurized, which makes the vane pressure
balanced and pushed radially by the centrifugal force. If the
blade root is not pressurized, the vane retracts under the action
of the pressure force on its tip area. Then, the vane will be fired
when the root is pressurized, which takes place four times per
revolution, to insure the required tightness. The vane firing
will cause severe damage to the cam’s inner surface.
• The vane separates two chambers of different pressures, with
the high pressure facing the vane leading side (see Fig. 4.34c).
In the case of single-vane design, the root should be pressurized
to insure the required tightness. The vane extension force is