The efficiency of a hydraulic system in construction machinery is primarily determined by the volumetric efficiency of the hydraulic pump. When this efficiency drops to 72%, routine maintenance, such as replacing bearings and aged seals, becomes necessary. Additionally, if the clearance between friction pairs exceeds acceptable limits, repair or replacement is required to restore optimal performance. This paper discusses the operation and maintenance of axial piston pumps, focusing on their design and upkeep.
Hydraulic pumps can be classified into two types based on their oil supply method: self-priming and pressure-fed. Most pressure-fed pumps rely on an air pressure tank or a charge pump to supply pressurized oil to the pump inlet. In contrast, self-priming pumps have their own internal mechanism for drawing in oil without external assistance.
When using a pressure-fed system, it's essential to wait for the hydraulic reservoir to reach the required pressure before starting the machine. If the pressure is too low, it may lead to cavitation, which can cause abnormal wear on the swashplate and pressure plate. For pumps with a charge pump, operators should check the pump’s condition at least once or twice daily after 3,000 hours of use. Any unusual noise, reduced speed, or erratic movement should prompt immediate inspection of the charge pump, including checking for impeller damage or excessive internal gear clearance.
Self-priming pumps require maintaining the hydraulic fluid level above the minimum mark to ensure proper lubrication. The higher the cleanliness of the hydraulic fluid, the longer the pump will last.
Bearings are critical components in piston pumps. If they develop clearance, it can compromise the integrity of the friction pairs and reduce the pump’s lifespan. Manufacturers typically state that bearings have an average service life of 10,000 hours, beyond which replacement is recommended. Without specialized testing equipment, visual inspection is the only way to assess bearing condition. Scratches or discoloration on the roller surfaces indicate the need for replacement.
When replacing bearings, it’s important to match the original model and specifications. Many piston pump bearings are high-load capacity, so using genuine parts from the manufacturer is advisable. If alternative brands are used, consulting a bearing expert is essential to maintain accuracy and load capacity.
Friction pair inspections and repairs are crucial for maintaining pump performance. The plunger rod and cylinder bore, for example, can be repaired through various methods, such as replacing copper sleeves, grinding, or using surface engineering techniques like electroplating or laser cladding. Similarly, the slipper and swashplate must be checked for clearance and wear. If the gap between the plunger ball head and slipper exceeds allowable limits, the entire set must be replaced.
Swashplates can develop concave surfaces over time, requiring precision grinding. If the surface is damaged, laser cladding or chromium welding can restore its integrity. All repairs must ensure that the original hardness, dimensional accuracy, and surface finish are maintained.
For flow plates and cylinder bodies, surface damage can be addressed through grinding or surface engineering. Proper alignment and sealing are essential, and leakage tests should be conducted after repairs to ensure a tight fit.
In conclusion, the lifespan of a piston pump depends on regular maintenance, the quality and cleanliness of the hydraulic fluid, and the use of genuine replacement parts. Avoiding counterfeit components, even if cheaper, is vital to prevent long-term damage. By following proper maintenance procedures, the effective life of the pump can be significantly extended.
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