Elimination of common faults in gear pumps
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At present, CB-B gear pumps are widely used in dump trucks and engineering machinery. These pumps are essential for various operating mechanisms, but they can experience common faults that affect performance. Below are detailed descriptions of the causes and troubleshooting methods to help users maintain and repair these pumps effectively.
1. **Causes and Elimination of Vibration and Noise**
**(1) Air Ingestion**
Air entering the pump can cause vibration and noise. This often happens when the pump body or cover has poor flatness, allowing air to be sucked in during operation. Similarly, if the gland is made of plastic and deforms due to temperature changes or damage, it may also allow air to enter. To resolve this, the pump body or cover should be ground on a flat plate using a "8" shape pattern or a surface grinder, ensuring the flatness does not exceed 5μm. The verticality of the plane and holes must also be maintained. For leaks around the pump cover and gland, sealing with epoxy resin is recommended.
The pump shaft is usually sealed with a skeleton oil seal. If the spring of the lip seal becomes detached, the oil is installed incorrectly, or the lip is worn, negative pressure at the rear end of the seal can draw in air. In such cases, replacing the oil seal is typically the best solution.
If the fuel tank has insufficient oil or the suction pipe is not submerged below the oil level, the pump may suck in air. To fix this, oil should be added to the correct level. Also, if the return line is above the oil surface, it may create temporary negative pressure, allowing air to re-enter the system. Therefore, the return line should be positioned below the oil level.
If the pump is installed too high relative to the oil level, especially at low speeds, the suction chamber may not generate enough vacuum, leading to air intake. Adjusting the height of the pump relative to the oil surface can solve this issue.
A clogged oil filter or one with an insufficient capacity can increase suction resistance and lead to air ingestion. Additionally, oversized inlet and outlet ports may also introduce air. Cleaning the filter or replacing it with a larger one can prevent both air intake and noise.
**(2) Mechanical Causes**
Misalignment between the pump and coupling can result in vibration and noise. Ensuring proper alignment of the coupling is essential.
Dirt or contaminated oil inside the pump can cause wear on components like gears, resulting in noise. Replacing the oil, reinforcing the filter, and disassembling the pump for inspection and cleaning can help. Severely worn gears should be repaired or replaced.
Damage or wear to internal parts, such as incorrect tooth profiles, excessive roughness, or improper meshing, can lead to vibration and noise. In such cases, replacing the gears or grinding the gear pair is necessary. Worn bearings or damaged needle rollers can also cause mechanical noise, so replacing them is crucial.
If the axial clearance is too small, or if burrs from the gears are not removed before assembly, it can cause internal leakage and reduce flow. Disassembling the pump, increasing the axial clearance, and smoothing the mating surfaces can resolve this issue.
**(3) Other Factors**
High oil viscosity can also contribute to noise, so using oil with the appropriate viscosity is important.
2. **Insufficient Output Flow**
High oil temperatures can reduce viscosity, increasing internal leakage and decreasing output flow. Checking the seals and addressing the root cause is essential. Using oil with the correct viscosity is also important. CB-B gear pumps cannot be reversed, so checking the direction of rotation is necessary. If the engine speed is too low, it can reduce flow, so identifying and fixing the issue is required.
3. **Poor Rotation**
Small axial or radial clearances can hinder rotation. Adjusting them properly is key. Dirt inside the pump should be removed by disassembling it. Incorrect assembly, such as driving the pin first instead of tightening the screws while rotating, can prevent the pump from working. Proper assembly procedures must be followed. Poor coaxiality between the pump and the engine coupling (within 0.1mm) should be corrected. All parts must be demagnetized before assembly. Damaged needle roller sleeves or broken needles require repair or replacement. Foreign objects blocking the oil outlet should be removed.
4. **Overheating**
Poor rotation can lead to overheating, so the same solutions apply. Oil viscosity that is too high or too low should be adjusted. Severe wear on side plates, bushings, or gear end faces requires repair or replacement. High ambient temperatures or a small fuel tank with poor cooling can also cause overheating.
5. **Repair of Major Components**
**(1) Gears**
For minor tooth wear, fine sandpaper or an oil stone can be used to remove burrs, then the gear meshing surface should be refined. Severe wear requires replacement. End face wear can be addressed by grinding, ensuring that the thickness difference between two gears is within 5μm. Perpendicularity and parallelism must also be within 5μm. Sharp edges should be rounded but not chamfered.
When gear meshing surfaces are worn, removing the burrs and changing the meshing orientation ensures even wear and extends the life of the gears.
**(2) Pump Body**
Wear on the inner cavity of the pump body, particularly on the suction side, can be addressed by flipping the symmetrical pump body or using plating techniques for asymmetric models.
**(3) Bearing Races**
Wear on the bearing race ends or inner bores can be repaired by grinding on a surface grinder, ensuring precision within 10μm. If severely worn, the bearing race may need to be replaced.
**(4) Long and Short Shafts**
Wear on the long and short shafts, especially where they contact the needle bearings, can be resolved with buffing or chrome plating. When reworking, maintaining the symmetry and parallelism of the keyways, as well as proper clearance, is essential. The shaft must not produce radial oscillation, and the coaxiality of the journals should be within 10–30μm.