bent axis type axial piston pump

BENT AXIS TYPE AXIAL PISTON PUMP

1. Construction

A typical 3D bent axis type axial piston pump is illustrated in Fig.4.17. The simplified line sketch of the same is shown in Fig.4.18.

This type of pump contains a cylinder block rotating with the drive shaft. As shown in Fig.4.17, the centerline of the cylinder block is set at an offset angle relative to the centerline of the drive shaft. The cylinder block has a number of pistons and cylinders arranged along a circle. The ball and socket joints connect the piston rods with the drive shaft flange. When the distance between the drive shaft flange and cylinder block changes, the pistons,move in and out of the cylinder. In order to provide alignment and positive drive, a universal link is used to connect the block to the drive shaft.

2. Operation

When the piston carrying body turns, the exit passages in the cylinder bores move along the control slots of a firmly positioned control plate and are thus connected alternatively to the suction or discharge pipelines.

3. Fixed-Displacement Bent Axis Piston Pump

In fixed displacement pumps, the pumps are mounted in a fixed casing so that swing (or offset) angle cannot be adjusted. So the fixed displacement of the piston and hence the constant discharge of fluid are achieved.

4. Variable-Displacement Bent Axis Piston Pump

In variable-displacement pumps, the swing (or offset) angle can be varied. Because the volumetric displacement of the pump varies with the offset angle. The variation in pump displacement with respect to offset angle is schematically illustrated in Fig.4.19.

As could be seen from Fig.4.19, the increase in the offset angle (0) will increase the piston stroke and hence the fluid displacement. When the offset angle is zero, then the displacement will be zero. However, for practical reasons, is to be varied from 0° to a maximum of about 30°.

5. Volumetric Displacement and Theoretical Flow Rate of an Axial Piston Pump

For any axial piston pump, the volumetric displacement and theoretical flow rate can be determined as follows:

Let θ = Offset angle in degrees,

S = Piston stroke in m,

D = Piston circle diameter in m,

d = Diameter of piston in m,

A = Cross-sectional area of the piston in m2 = π /4 d2,

Y = Number of pistons, and

N = Rotor speed in rpm.

From the geometry of a piston (Fig.4.20), we get