Yuken Variable Displacement Vane Pumps

Vane pumps can be transformed to the unbalanced type by making the center of the round cam ring eccentric to the rotating shaft; this type provides a pair of suction and discharge processes. The pumps can also be transformed to the variable displacement type by making the cam ring at the maximum eccentricity concentric with the shaft (the output flow continuously reduces to zero). The variable displacement type is not pressure balanced and has a greater force in the radial direction than the fixed displacement type.

Figure 2.16 shows the appearance and cross sectional view of a typical small-sized variable displacement vane pump. It is a pressure compensator type with a mechanism that uses a spring to make the cam ring eccentric to the maximum level at a low pressure. However, when the pressure reaches a preset level, the hydraulic power exceeds the spring force to reduce the eccentricity.

Small-sized Variable Displacement Pump

The variable displacement vane pumps that offer displacements of 8 to 22 cm3/rev (.488 to 1.34 cu.in./rev) and operate at 7 MPa (1 015 psi) or less are widely used in small machine tools because of inexpensiveness and low noise level. Those that offer a displacement of 160 cm3/rev (9.76 cu.in./rev) and operate at 16 MPa (2 321 psi) or less are also available.

Similar to the piston pumps, large-volume variable displacement pumps with load sensing control are commercially supplied; however, the variable displacement pumps are generally used in low/middle pressure ranges.

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