Application of German REXROTH piston pumps in hydraulic systems

Brand

REXROTH/Germany Rexroth

Application Areas

Medical & Health, Environmental Protection, Food/Agricultural Products, Agriculture, Forestry, Animal Husbandry & Fishery, Comprehensive

Rexroth piston pumps are an important component of hydraulic systems. They rely on the reciprocating motion of the piston within the cylinder to change the volume of the sealed working chamber, thus achieving oil suction and pressure. Piston pumps offer advantages such as high rated pressure, compact structure, high efficiency, and convenient flow regulation, and are widely used in high-pressure, high-flow, and flow-adjustable applications, such as hydraulic presses, construction machinery, and ships.

Rexroth piston pumps are a type of reciprocating pump, belonging to the category of volumetric pumps. Their pistons are driven by the eccentric rotation of the pump shaft, reciprocating in motion. Both their suction and discharge valves are one-way valves. When the piston is pulled outward, the pressure in the working chamber decreases, the outlet valve closes, and when the pressure is lower than the inlet pressure, the inlet valve opens, allowing liquid to enter. When the piston is pushed inward, the pressure in the working chamber increases, the inlet valve closes, and when the pressure is higher than the outlet pressure, the outlet valve opens, allowing liquid to exit. When the drive shaft rotates the cylinder block, the swashplate pulls the plunger out or pushes it back into the cylinder block, completing the oil suction and discharge process. The oil in the working chamber formed by the plunger and cylinder bore communicates with the pump's suction and discharge chambers through the distribution plate. A variable displacement mechanism is used to change the swashplate's angle; adjusting the swashplate's angle changes the pump's displacement.

The gears and shafts of the REXROTH radial piston pump are integrated, using a through-hardening process for a longer service life. The "D" type bearing incorporates a forced lubrication mechanism, allowing polymer to pass through the bearing surface and return to the pump inlet side, ensuring effective lubrication of the rotating shaft.

Rexroth piston pumps are a brand under Bosch Rexroth. REXROTH is not only a world-leading company but also one of the world's most renowned high-tech enterprises. For over 50 years, the Bosch Rexroth Group and its business units have been dedicated to developing high-tech products in the field of professional hydraulic transmission. Currently, Chenming Electromechanical is the main distributor in mainland China. Rexroth products are indeed superior because, in the global market, no other brand currently offers customers a comprehensive range of transmission and control technologies, combining specialization and integration. This is why Bosch-Rexroth has become a global leader in hydraulic transmission, control, and motion technologies.

Rexroth Piston Pump Flow Problems (Germany)

(1) Insufficient suction. Caused by excessive resistance in the suction line or insufficient replenishment. For example, excessive pump speed, low oil level in the tank, air leakage in the inlet pipe, or clogged oil filter.

(2) Excessive leakage. Caused by excessive pump clearance and poor sealing. For example, scratches on the distributor plate by metal fragments or iron filings, resulting in end-face leakage; poor fit of the check valve sealing surface in the variable displacement mechanism; sand holes or scratches on the pump body and distributor plate support surfaces. The location of the pump damage can be determined by inspecting the hydraulic oil for foreign matter mixed in the pump body.

(3) Insufficient swashplate angle results in low pump displacement. This requires adjusting the variable piston to increase the swashplate angle. Non-zero discharge at neutral position

The neutral position of a variable displacement axial piston pump is when the swashplate angle is zero, at which point the pump's output flow should be zero. However, sometimes the neutral position deviates from the midpoint of the adjustment mechanism, and flow is still output even at the midpoint. This is caused by misalignment, loosening, or damage to the controller, requiring readjustment, tightening, or replacement. Insufficient pump angle holding force and wear on the tilt angle trunnion can also cause this phenomenon.

Fluctuations in output flow of German REXROTH piston pumps

Fluctuations in output flow of German REXROTH piston pumps are related to many factors. For variable displacement pumps, this can be attributed to poor control of the variable displacement mechanism, such as foreign objects entering the mechanism, causing scratches, wear, or damage on the control piston, resulting in unstable piston movement. Insufficient amplifier power or damaged parts, and poor damping efficiency in spring-loaded control pistons can also cause unstable piston movement. Unstable flow is often accompanied by pressure fluctuations. These types of faults generally require disassembling the hydraulic pump, replacing damaged parts, increasing damping, improving spring stiffness, and increasing control pressure.

Abnormal Output Pressure of German REXROTH Piston Pumps

The output pressure of German REXROTH piston pumps is determined by the load and is approximately proportional to the input torque. There are two types of abnormal output pressure:

(1) Low Output Pressure

When the pump is in self-priming mode, if there is air leakage in the inlet line or significant leakage in the hydraulic cylinder, check valve, or directional valve in the system, the pressure will not rise. This requires finding the leak, tightening, or replacing the seals to increase the pressure. If the relief valve is faulty or the adjusted pressure is too low, the system pressure will also not rise; the pressure should be readjusted or the relief valve repaired. If the hydraulic pump cylinder body and distributor plate are misaligned, causing significant leakage, the cylinder body may crack in severe cases; in this case, the mating surfaces should be re-ground or the hydraulic pump replaced.

(2) High Output Pressure

If the circuit load continues to increase, the pump pressure will also continue to rise, which is normal. If the load is constant and the pump pressure exceeds the required load value, the hydraulic components other than the pump, such as directional valves, pressure valves, transmission devices, and return lines, should be checked. If the maximum pressure is too high, the relief valve should be adjusted. Vibration and Noise

Vibration and noise occur simultaneously. They not only harm machine operators but also pollute the environment.

(1) Mechanical Vibration and Noise

Noise is generated by misalignment or jamming of the pump shaft and motor shaft, damage to bearings and couplings of rotating shafts, broken elastic pads, and loose assembly bolts. For pumps operating at high speeds or transmitting large amounts of energy, regular inspections are necessary to record the amplitude, frequency, and noise of each component. Resonance will occur if the pump's rotational frequency matches the natural frequency of the pressure valve; this can be eliminated by changing the pump's speed.

(2) Noise Generated by Liquid Flow in Pipelines

Noise is generated by factors such as an excessively narrow inlet pipe, insufficient flow capacity or blockage of the inlet filter, air intake in the inlet pipe, excessively high oil level, insufficient oil suction due to low oil level, and liquid hammer in high-pressure pipelines. Therefore, proper design of the oil tank and correct selection of filters, oil pipes, and directional valves are essential. Our company mainly deals in European and American products. We have offices in Germany and the United States, allowing us to source brands from any European country. Our key German brands include: BURKERT, DEMAG, HAWE, REXROTH, HYDAC, PILZ relays, FESTO, IFM sensors, E+H, HEIDENHAIN, P+F sensors, SICK, TURCK, and HIRSCHMANN industrial switches. German brands: Hengstler, Murr, Schmersal, Samson, EPRO (Emerson Group)

American brands: MOOG, ASCO, MAC, NUMATICS, PARKER, VICKERS, ROSS

British brands: Norgren

Italian brands: OMAL, ATOS, CAMOZZI, UNIVER, Camozzi