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Pollution, Harm and Prevention of Oil in Hydraulic System of Tunnel Boring Machine

Nov. 13, 2020

Tunneling Boring Machine01


The hydraulic system of tunneling boring machine mainly includes several major systems such as cutter head drive system, propulsion articulation system, screw conveyor system (EPB), segment assembly machine system, grouting pump system, hydraulic oil filter circulation system, etc. , According to different models, different auxiliary systems will be equipped. The poor working environment of the tunnel boring machine, human error in operation and other reasons have caused too many accidents in which the hydraulic system was contaminated, and eventually caused the failure and shutdown of the hydraulic equipment, which seriously affected the construction progress.


Sources of contaminants in hydraulic systems

The oil contamination of the hydraulic system refers to the presence of substances in the oil that are harmful to the reliability of the system and the life of the components. For tunnel boring machines, there are mainly external intrusions, system residues, and system products.

①External intrusions

Because the roadheader works underground and the construction environment is poor, the hydraulic system will inevitably be invaded by external pollutants during the maintenance and work process. During the refueling process, the irregular operation of the operator may also cause a lot of Foreign body intrusion.

②System residues

The improper operation of hydraulic systems and components during processing, assembly, storage and transportation can also cause contaminants to be mixed into the system, such as metal chips, welding slag, dust and cleaning solvents.

③System product

The wear debris generated by the friction between the moving parts of the hydraulic system and the rust flakes generated by the internal surface corrosion are the system products.

Tunneling Boring Machine03

The hazards of hydraulic system pollution

About 80% of hydraulic system failures are caused by oil pollution, so the control of oil pollution is very necessary.

The main hazards of pollutants are as follows:

1. The spool is stuck, causing the hydraulic valve to malfunction, and it will cause a shutdown in severe cases;

2. The filter is blocked, the pump is difficult to suck oil, and the pump heats up and produces noise. When the blockage is serious, the filter screen will be broken due to resistance;

3. Pollutants enter the pump, accelerate the wear of the pump, increase internal leakage, and reduce the efficiency and life of the hydraulic pump;

4. Wear aggravates oil pollution, causing abnormal wear of pumps, motors, cylinders, and valves, leading to failure.

Different hydraulic components have different sensitivity to solid particles, see the table below.



Sensitive particle size (μm)

Hydraulic valve


Axial piston pump/motor


Radial piston pump/moto


Vane pump



The table shows the particle sensitive size of a single element, and the sensitive size of the hydraulic system is usually measured by the smallest sensitive size in the system. According to actual experience, the particle sensitive size of the overflow valve is 5 microns.


Prevention of hydraulic system contamination

The pollution prevention of hydraulic system oil runs through the entire process of hydraulic system design, manufacturing, use and maintenance.

The pollution of the hydraulic system can not be complete, but through pollution control, the pollution degree of the oil is kept within the range of the key hydraulic components of the system to the greatest extent. Although a higher-precision filter in the hydraulic system can control oil pollution, it is still necessary to carry out strict control in all aspects of the whole process in order to fundamentally improve the system performance.

At present, as online status detection has gradually attracted people's attention, some roadheader manufacturers have selected automatic particle counters and other aspects, which can communicate with the host computer through data transmission. The monitor continuously monitors the pollution degree, and the on-site maintenance personnel can go through uninterrupted inspections to ensure that the pollution degree of the oil is kept within a certain range, thereby ensuring the reliable operation of the entire hydraulic system.

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