Common fault handling for repair of Rexroth piston pumps

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Repair of Rexroth piston pumps, working principle, and handling of common faults (1): Low output pressure. When the pump is in self-priming mode, air leakage in the oil inlet pipeline, or significant leaks in components such as hydraulic cylinders, check valves, and directional control valves within the system, can all prevent the pressure from rising. This requires identifying the leak, tightening or replacing the seals, which will increase the pressure. If the relief valve is faulty or the set pressure is low, the system pressure will not rise; the pressure should be adjusted again or the relief valve should be repaired. If a deviation between the cylinder block of the hydraulic pump and the valve plate causes severe leakage, and in serious cases the cylinder block may even crack, the mating surfaces should be re-ground or the hydraulic pump replaced. (2) Excessively high output pressure: If the load in the circuit continues to increase, the pump pressure will also rise, which is normal. If the load remains constant and the pump pressure exceeds the pressure required by the load, then hydraulic components other than the pump should be checked, such as direction valves, pressure valves, drive mechanisms, and return pipelines. If the maximum pressure is too high, the relief valve should be adjusted. 5. Vibration and noise: Vibration and noise occur simultaneously. They not only pose a hazard to machine operators but also cause pollution to the environment. (1) Mechanical vibration and noise can be generated by factors such as misalignment or seizure of the pump shaft and motor shaft, damage to the bearings and couplings of the rotating shafts, damaged elastic pads, and loose mounting bolts. For pumps that operate at high speeds or transfer large amounts of energy, regular inspections are necessary to record the amplitude, frequency, and noise of various components. If the rotation frequency of the pump coincides with the natural frequency of the pressure valve, resonance will occur; the pump’s speed can be adjusted to eliminate this resonance. (2) Noise generated by fluid flow in the pipes can be caused by a too narrow oil inlet pipe, an oil filter with insufficient flow capacity or that is clogged, air being drawn into the oil inlet pipe, excessive viscosity of the oil, insufficient oil intake due to an overly low oil level, and water hammer occurring in high-pressure pipes. Therefore, the fuel tank must be properly designed, and the oil filters, oil pipes, and directional valves must be selected correctly. 6. Overheating of the hydraulic pump. There are two reasons for excessive heating of the hydraulic pump: one is heat generated by mechanical friction. Since the moving surface is in a state of dry or semi-dry friction, heat is generated through the friction between the moving parts. The second is heat generation due to liquid friction. High-pressure oil leaks into the low-pressure chamber through various gaps, and a large amount of hydraulic energy is converted into heat energy. Therefore, by properly selecting the clearance between moving parts, the volume of the oil tank, and the cooler, it is possible to prevent excessive heating of the pump as well as excessively high oil temperatures. Furthermore, a clogged return oil filter that causes excessive back pressure in the return oil can also lead to high oil temperatures and overheating of the pump. 7. The main reasons for oil leakage in piston pumps are as follows: (1) Damage to the main shaft seal or defects/scratches on the shaft ； (2) Excessive internal leakage leads to an increase in pressure at the oil seal, thereby damaging the oil seal or causing it to be pushed out ； (3) The oil drain pipe is too thin and too long, causing oil leakage at the seal ； (4) The external oil pipe of the pump is loose, the pipe fittings are damaged, and the gaskets are aged or cracked ； (5) Bolts of the variable adjustment mechanism are loose, and the seal is damaged ； (6) Sand holes or poor welding in the cast iron pump casing are common issues encountered during the repair of hydraulic pumps. For pumps such as Rexroth piston pumps, these types of repair problems are something we must be familiar with. Rexroth holds a large market share in China; therefore, knowing how to repair Rexroth piston pumps is an essential skill for anyone working in hydraulic pump maintenance.