Vane Pumps in Hydraulic Systems

Working Principle

Single-acting vane pumps, a vital category in hydraulics pumps technology, consist of a rotor, stator, vanes, end plates, and other components as illustrated in Figure 4-12. The stator features a cylindrical inner surface and is mounted eccentrically relative to the rotor, creating an offset distance (e) between their centers.

Vanes are installed in slots within the rotor and can slide freely. As the rotor rotates, centrifugal force and pressure from oil at the vane roots push the vane tips against the inner surface of the stator. This creates sealed chambers between adjacent vanes, the stator, rotor, and side plates.

In hydraulics pumps of this design, as the rotor turns in the direction shown in Figure 4-12, vanes on the right side gradually extend, increasing the volume of the sealed working chambers. This volume increase creates a partial vacuum, drawing oil from the reservoir through the suction port and into these chambers via the port plate's suction windows (shown as dashed areas in Figure 4-12).

Figure 4-12: Working principle of a single-acting vane pump

Conversely, vanes on the left side of Figure 4-12 are pushed back into the rotor slots by the stator's inner surface, reducing the volume of the sealed working chambers. This compression forces oil through the pressure port windows in the port plate and out of the pump, completing the discharge process.

A land area separates the suction and discharge chambers in these hydraulics pumps, preventing internal leakage between them. Since the pump completes one suction and discharge cycle per rotor revolution as the vanes slide in and out once, it is classified as a single-acting vane pump.

Flow Calculation

Figure 4-13: Displacement calculation diagram for single-acting vane pump

In hydraulics pumps terminology, displacement (V) is determined by the product of the number of sealed working chambers (Z) and the volume change (ΔV) of each chamber during the discharge phase, as shown in Figure 4-13. For single-acting vane pumps, the volume change per chamber during one rotor revolution can be approximated as the difference between two扇形体积 (sector volumes).

Assuming the stator inner radius is R, stator width is B, and the angle between two adjacent vanes is β, the volume change (ΔV) for one chamber can be calculated as:

ΔV ≈ (1/2) * B * [(R + e)² - (R - e)²] * (β/2π)

Simplifying this equation for hydraulics pumps design results in:

Where:

• R = stator inner radius
• e = eccentricity between rotor and stator
• B = stator width
• Z = number of vanes

Therefore, the total displacement (V) of single-acting hydraulics pumps is:

When considering pump speed (n) and volumetric efficiency (ηₐ), the theoretical flow rate (qₜ) and actual flow rate (q) of these hydraulics pumps can be calculated as:

Characteristics and Performance

The flow output of single-acting hydraulics pumps exhibits pulsation characteristics. Theoretical analysis shows that increased vane count reduces flow pulsation. Additionally, pumps with an odd number of vanes demonstrate lower pulsation rates compared to those with even numbers.

A key advantage of single-acting vane pumps in hydraulics pumps systems is their variable displacement capability. By adjusting the eccentricity (e) between the rotor and stator, the pump's output flow can be controlled, justifying their classification as variable displacement pumps.

However, a significant disadvantage is the unbalanced pressure between suction and discharge chambers, which creates substantial radial loads on the bearings. This characteristic has led to their alternative classification as non-pressure-balanced hydraulics pumps.

Working Principle

Double-acting vane pumps represent another fundamental design in hydraulics pumps technology, distinguished by their balanced pressure configuration and fixed displacement characteristics. These pumps feature an elliptical or figure-eight shaped stator that creates two separate suction and discharge zones.

Similar to their single-acting counterparts, double-acting hydraulics pumps utilize vanes sliding within rotor slots. These vanes maintain contact with the stator inner surface through centrifugal force and pressure from the vane roots, creating sealed chambers between adjacent vanes.

The unique stator profile in these hydraulics pumps causes each vane to extend and retract twice during one rotor revolution. This results in two complete suction and discharge cycles per revolution, giving rise to the designation "double-acting."

Figure 4-14: Internal structure of a double-acting vane pump

As the rotor turns in double-acting hydraulics pumps, vanes move into expanding chambers during the suction phase, drawing fluid into the pump. As the rotor continues to rotate, these chambers contract, forcing fluid out through the discharge ports. The symmetric design creates two suction zones and two discharge zones positioned opposite each other.

This symmetrical arrangement in hydraulics pumps results in balanced radial forces on the rotor and bearings, significantly reducing wear and extending service life compared to unbalanced designs. The port plate incorporates internal passages that connect opposite suction and discharge zones, ensuring proper fluid distribution throughout the pump cycle.

Flow Calculation

Figure 4-15: Flow calculation parameters for double-acting vane pump

The displacement calculation for double-acting hydraulics pumps considers the volume change in each working chamber during both discharge phases of one rotor revolution. The stator's elliptical profile creates two distinct radii: the major radius (R) and the minor radius (r).

For these hydraulics pumps, the volume change per chamber (ΔV) during one complete revolution can be calculated based on the difference between the maximum and minimum chamber volumes:

ΔV = 2 * B * (R² - r²) * (β/2π)

With Z vanes, the total displacement (V) of double-acting hydraulics pumps is:

Where:

• R = maximum stator radius (major axis)
• r = minimum stator radius (minor axis)
• B = stator width
• Z = number of vanes

The theoretical flow rate (qₜ) for these hydraulics pumps is therefore:

Accounting for volumetric efficiency (ηₐ), the actual flow rate (q) of double-acting hydraulics pumps is:

It's important to note that in double-acting hydraulics pumps, the eccentricity cannot be adjusted, resulting in a fixed displacement and constant flow rate at a given speed, which classifies them as fixed displacement pumps.

Characteristics and Applications

Double-acting vane pumps offer several advantages in hydraulics pumps systems, primarily their balanced hydraulic design that eliminates radial bearing loads. This feature allows them to operate at higher pressures than single-acting designs, typically up to 160-210 bar (2300-3000 psi) in industrial applications.

These hydraulics pumps exhibit excellent flow characteristics with low pulsation, especially when designed with a higher number of vanes. The even number of vanes (often 10-12) combined with the symmetric stator design results in smooth operation and reduced noise levels compared to many other positive displacement pumps.

While double-acting hydraulics pumps lack the flow adjustability of their single-acting counterparts, they offer superior efficiency and longer service life in applications requiring constant flow. Common applications include machine tools, plastic injection molding machines, and automated industrial equipment where consistent performance is critical.

The robust construction of double-acting vane pumps makes them well-suited for continuous-duty applications in hydraulics pumps systems, providing reliable operation even with contaminated fluids when properly filtered. Their compact design also makes them ideal for installations with space constraints.