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Causes of Failure of Hydraulic Pump and Improvement Method

Hydraulic pump is the power component of the hydraulic system. Its function is to convert the mechanical energy of the prime mover into the pressure energy of the liquid. It refers to the oil pump in the hydraulic system, which provides power to the whole hydraulic system. Hydraulic pumps generally have gear pumps, vane pumps and plunger pumps.

The principle of hydraulic pump is a kind of hydraulic component which provides pressurized liquid for hydraulic transmission, and it is also a kind of pump. Its function is to convert the mechanical energy of power engines (such as motors and internal combustion engines) into the pressure energy of liquids. The working principle of the single plunger pump is shown in the figure. The cam is rotated by a motor. When the cam pushes the plunger upward, the sealing volume formed by the plunger and the cylinder block decreases, and the oil is extruded from the sealing volume and is discharged through the one-way valve to the desired place. When the cam rotates to the downward part of the curve, the spring forces the plunger downward to form a certain degree of vacuum, and the oil in the tank enters the sealing volume under the action of atmospheric pressure. The cam makes the plunger rise and fall continuously, the sealing volume decreases and increases periodically, and the pump sucks and discharges oil continuously.

1. Disadvantage Phenomenon and Cause Analysis

In the maintenance process, we can find the reasons for the shortcomings from the following three points, and improve the system interruption:

(1) Check the internal leakage of the boom cylinder. The simple way is to raise the arm and see if it can land freely. If the drop is obvious, remove the cylinder and inspect it. If the seal ring has worn out, it should be replaced.

(2) Check the control valve. First, clean the safety valve, check whether the spool can wear, such as wear should be replaced. If there is no change after the safety valve is installed, then check the wear condition of the control valve spool. The clearance limit is usually 0.06mm, and the wear should be changed seriously.

(3) Measure the pressure of the hydraulic pump. If the pressure is on the low side, the adjustment will be stopped and the pressure can not be adjusted, which indicates that the hydraulic pump is seriously worn.

Generally speaking, the main reasons why the boom can not be lifted with load are as follows:

A. Serious wear of hydraulic pump. In low-speed operation, the pump reveals serious; in high-speed operation, the pump pressure slightly improved, but due to the wear and internal leakage of the pump, the volume efficiency significantly decreased, it is difficult to reach the rated pressure. The long working time of hydraulic pump aggravates the wear and tear, and the oil temperature rises, which constitutes the wear of hydraulic components and the aging and damage of sealing parts, loss of sealing ability, hydraulic oil degeneration, and then cause shortcomings.

B. The selection of hydraulic components is unreasonable. The specifications of the boom cylinder are 70/40 non-standard series, and the seals are also non-standard parts. The manufacturing cost is high and the seals are inconvenient to change. The small cylinder diameter of the boom cylinder will inevitably make the setting pressure of the system high.

C. The design of hydraulic system is unreasonable. The control valve and the full hydraulic steering gear are connected in series with a single pump. The setting pressure of the safety valve is 16 MPa, and the rated working pressure of the hydraulic pump is 16 MPa. Hydraulic pumps often work under full load or long time overload (high pressure), and the system has hydraulic impact, long-term no oil change, hydraulic oil is polluted, worsening the wear of hydraulic pumps, resulting in hydraulic pump shell cracking (such shortcomings have been found later).

2. Improvement and effect

(1) Improve the design of hydraulic system. After many demonstrations, and then using the standardized priority valve and load sensing full hydraulic steering gear, the new system can distribute the flow to the steering system according to the request of steering, regardless of the load size and steering wheel speed, it can ensure sufficient oil supply, and the rest can be supplied to the working device circuit, thus eliminating the problem. The power loss is caused by excessive oil supply to the steering circuit, which improves the system efficiency and reduces the working pressure of the hydraulic pump.

(2) Optimize the exterior design of the boom cylinder and hydraulic pump to reduce the working pressure of the system. After optimization calculation, the standard series 80/4 of the boom cylinder is adopted. The displacement of hydraulic pump has been improved from 10ml/r to 14ml/r, and the system pressure has been set to 14MPa, which satisfies the requirement of lifting force and speed of the boom cylinder.

(3) In the course of operation, attention should also be paid to the correct use and maintenance of loaders, regular addition or replacement of hydraulic oil, adhere to the cleanliness of hydraulic oil, and strengthen routine inspection and maintenance.