What Types of KP Gear Pumps Are There?

KP gear pumps, a common designation for a range of external gear pumps, are fundamental components in hydraulic systems across numerous industries. Their operation, based on the meshing and unmeshing of two identical gears within a closely fitted housing, provides a reliable method for transferring fluids. The classification of these pumps is not based on a single characteristic but rather on several key engineering and design aspects. Understanding these variations is crucial for selecting the appropriate pump for a specific application, whether in mobile machinery, industrial presses, or lubrication systems.

1. Gear Design and Tooth Profile

The geometry of the gears themselves is a primary differentiator, directly impacting performance characteristics such as noise level, flow ripple, and pressure capability.

• Spur Gears: This is the basic and common design. The gear teeth are straight and parallel to the axis of rotation. Spur gears are relatively simple to manufacture and are cost-effective. However, they engage with a single line of contact, which can higher noise levels and more pronounced flow pulsation compared to other designs. This pulsation can manifest as vibration in the hydraulic system. They are suitable for a wide range of general-purpose applications where moderate noise is acceptable, such as in simple power units or transfer pumps.
• Helical Gears: In this design, the gear teeth are cut at an angle to the axis, forming a helix. This geometry allows for a gradual engagement where multiple teeth are in contact at any given time. This results in smoother fluid displacement, significantly reduced noise and vibration, and less flow pulsation. The trade-off is the introduction of an axial thrust force that must be managed by the pump's bearings, which can influence design complexity and cost. Helical gear pumps are often specified for applications requiring quieter operation, such as in industrial machinery operating in close proximity to personnel.
• Herringbone Gears: This design can be viewed as two opposing helical gears mounted side-by-side on the same shaft. The axial thrust forces generated by each helix cancel each other out, eliminating the need for heavy-duty thrust bearings. Herringbone gears offer the smooth, quiet operation of helical gears without the associated axial load, but they are more complex and expensive to manufacture. Their use is typically reserved for high-performance or high-pressure applications where operational smoothness and reliability are critical.

2. Construction Materials and Sealing Options

The materials used for the critical components of a KP gear pump are selected based on the fluid being pumped, operating pressure, and environmental conditions.

• Component Materials: The gear set, shaft, and housing material choices are dictated by application requirements. For common industrial hydraulic oil applications, gears and shafts are often made from case-hardened steel for strength and wear resistance, housed in a cast iron body. For pumping corrosive chemicals, food, or pharmaceuticals, the wetted parts might be constructed from stainless steel. In applications where weight is a concern, such as in aerospace, aluminum housings may be used. The use of engineered plastics or composites for gears is also seen in low-pressure, corrosion-resistant applications.
• Bearing Types: The bearings that support the gear shafts are critical for pump longevity. Journal bearings, often made from bronze or sintered metal, are common and can handle high loads while providing inherent damping. For higher speed applications, rolling element bearings (ball or roller bearings) may be used to reduce friction. The choice affects the pump's speed capability, noise level, and tolerance to contamination.
• Shaft Sealing Systems: Preventing fluid leakage along the drive shaft is essential. The common sealing method is a lip seal, which is a cost-effective solution for lower-pressure systems. For higher pressures or more demanding duties, mechanical seals are employed. These seals consist of two highly flat, spring-loaded faces that rotate against each other, providing a more robust and durable seal. The choice between them depends on pressure, speed, fluid compatibility, and expected service life.