There are many factors that affect the service life of hydraulic pumps, in addition to the pump's own design and manufacturing factors, as well as the selection of some components related to pump use (such as couplings, oil filters, etc.), and the operation during trial operation. This article presents several of its own insights on this matter.
1. Analysis of related components
1.1 Coupling
Selection of couplings. The hydraulic pump drive shaft cannot withstand radial and axial forces, so it is not allowed to directly install pulleys, gears, and sprockets at the shaft end. Usually, a coupling is used to connect the drive shaft and the pump drive shaft. If the coaxiality between the pump and the coupling exceeds the standard due to manufacturing reasons, and there is a deviation during assembly, then as the pump speed increases, the centrifugal force increases and the coupling deforms. The large deformation also increases the centrifugal force, causing a vicious cycle, resulting in vibration noise and affecting the service life of the pump. In addition, there are also influencing factors such as loose coupling pins not tightened in a timely manner, and rubber ring wear not replaced in a timely manner.
Assembly requirements for couplings: The coaxiality error of the two shafts of the rigid coupling should be ≤ 0.05mm; The coaxiality error of the two shafts of the elastic coupling is ≤ 0.1mm; The angle error between the two axes is less than 1 °; The distance between the drive shaft and the pump end should be maintained at 5-10mm.
1.2 Hydraulic oil tank
Selection of hydraulic oil tank. The main function of the hydraulic oil tank in the hydraulic system is to store oil, dissipate heat, separate the air contained in the oil and eliminate foam. When selecting a fuel tank, the capacity should be considered first. Generally, for mobile equipment, the maximum flow rate of pump Z should be 2-3 times, and for fixed equipment, it should be 3-4 times; Secondly, consider the oil level in the fuel tank. When all hydraulic cylinders in the system are extended, the oil level in the tank must not be lower than the Z-low oil level. When the cylinders are retracted, the oil level must not be higher than the Z-high oil level; Considering the structure of the fuel tank, the traditional partition inside the tank cannot settle dirt. A vertical partition should be installed along the longitudinal axis of the tank, leaving a gap between one end of the partition and the end plate of the tank to connect the spaces on both sides of the partition. The inlet and outlet of the hydraulic pump are arranged on both sides of the partition at the disconnected end, so that the distance between the inlet and return oil is Z far, and the hydraulic tank plays a more important role in heat dissipation.
Installation of hydraulic oil tank. According to the different installation positions, it can be divided into top mounted, side mounted, and bottom mounted types.
The upward mounted oil tank installs hydraulic pumps and other devices on a rigid upper cover plate, which has a compact structure and wide application. In addition, heat dissipation fins can be cast on the outer shell of the fuel tank to enhance the heat dissipation effect, thereby improving the service life of the hydraulic pump.
Side mounted oil tank is a device that installs hydraulic pumps and other devices next to the oil tank. Although it occupies a large area, it is easy to install and maintain. It is usually used when the system flow and oil tank capacity are large, especially when one oil tank supplies oil to multiple hydraulic pumps. Due to the side mounted oil tank having a higher oil level than the hydraulic pump suction port, it has a good suction effect.
The bottom mounted oil tank places the hydraulic pump under the tank, which is not only convenient for installation and maintenance, but also greatly improves the suction capacity of the hydraulic pump.
1.3 Oil Filter
Selection of oil filter. Generally, pollutants with a particle size below 10 μ m have little effect on the pump, while those larger than 10 μ m, especially above 40 μ m, have a significant impact on the pump's service life. Solid pollution particles in hydraulic oil can easily cause increased wear on the surfaces of relative moving parts inside the pump. Therefore, it is necessary to install oil filters to reduce the degree of oil pollution. Filtering accuracy requirements: 10-15 μ m for axial piston pumps, 25 μ m for vane pumps, and 40 μ m for gear pumps. The pollution and wear of the pump can be controlled within the allowable range. At present, high-precision oil filters are increasingly widely used, which can greatly extend the service life of hydraulic pumps.
Installation of oil filter. There are three situations: the structure of the oil filter in the oil suction path is simple, and its function is to prevent larger particulate pollutants from being sucked into the pump during oil suction. Generally, a low precision filter element is used, and the Z high filtration accuracy does not exceed 30-50 μ m. In order to facilitate maintenance, the oil filter should be installed on the top or side of the oil tank, and its flow capacity should be considered to be more than twice the flow rate of the hydraulic pump Z to prevent the pump from sucking up; The pressure oil filter is installed in the downstream pressure pipeline of the hydraulic pump to deliver clean pressure oil to the hydraulic system. High precision oil filters with a filtration accuracy of 3-20 μ m are usually used, and their flow capacity should not be less than the large flow rate of the pressure oil circuit Z; The return oil filter is installed after the main return oil pipe to filter out the pollutants that enter the system and are generated inside the system. High precision oil filters are usually used. According to recent pollution control system theory, the oil in the fuel tank should reach a certain level of cleanliness. At the same time, to prevent the filter element from clogging and causing excessive pressure before and after the filter, a filter element clogging transmitter should be installed to facilitate timely replacement of the filter element.
1.4 Heat exchanger
The hydraulic system allows the oil temperature to be between 15-80 ℃, and the optimal temperature for Z is between 25-55 ℃. During the operation of hydraulic systems, mechanical losses, pressure losses, and volume losses are inevitably generated. All of these losses are converted into heat, and most of the heat is dissipated to the surrounding space through the oil tank and pipelines, causing the temperature of the oil tank to rise. If the oil temperature is too high, the oil will deteriorate and precipitate asphalt and other impurities, the viscosity of the oil will decrease, the leakage inside and outside the hydraulic pump will increase, the lubrication of the oil will be poor, the oil film will be easily damaged, and the wear of the relative sliding parts inside the pump will be intensified, greatly shortening the service life of the pump. Therefore, when the system temperature rises too high, an oil cooler must be installed. Coolers are divided into air-cooled, water-cooled, and chilled types, depending on the situation.
On the contrary, if the oil temperature is too low, the viscosity of the oil increases, the frictional resistance increases, and the hydraulic pump is difficult to start and absorb oil, which affects the use of the pump. Should the oil be heated before starting the pump in areas below 0 ℃? Connect to the pump body at a temperature above 15 ℃ and wait for the temperature of each component to rise above 15 ℃ before starting the hydraulic pump. To do this, a heater needs to be horizontally installed at the bottom of the oil tank to ensure that it is always immersed below the oil level.
2. Precautions for operation during operation
Before operation: Whether the installation of the hydraulic pump is accurate and reliable, whether the screws are tightened, and whether the installation of the coupling meets the requirements; Is the pump body filled with oil; Is the direction of the pump consistent with the inlet and outlet of the oil; Is the safety valve of the hydraulic system set to the specified pressure value.
During operation: Do not start rapidly at full speed during startup. The prime mover switch should be turned several times while the system is unloaded before continuous no-load operation. The purpose is to remove the air in the pipeline as much as possible. After 1-2 minutes of no-load operation without any abnormal phenomena, gradually load. During the loading process, there should be no abnormal vibration, noise, or leakage. Otherwise, immediately stop the machine for inspection, analysis, and troubleshooting.
After operation: If the pump is not used for a long time, the oil inside the pump should be drained and filled with oil with a lower acid value. The exposed machining surface should be coated with rust proof oil, and each oil port should be sealed with screw plugs to prevent dirt from entering.
From the above comprehensive analysis, it can be seen that the service life of a hydraulic pump is determined by the degree of damage and wear of its internal parts, but the degree of damage and wear of its internal parts is directly affected by the use of its external components. Therefore, the reasonable selection of relevant external components of the hydraulic pump and the correct operation and use of the hydraulic pump can greatly improve the service life of the pump.
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2025-03-19