Analysis of Heating Problems in Komatsu Hydraulic System

2025-02-03

1. Heating phenomenon and its hazards in hydraulic systems

The repair of hydraulic system heating in Komatsu excavator is a common phenomenon in excavator excavation, and it is also a complex soft problem that needs to be analyzed and dealt with. Under normal operating conditions, the oil temperature of the hydraulic system of the Komatsu PC200/400 excavator should be below 60oC (the temperature of the oil pump should be 5-10oC higher). If it exceeds this limit significantly, it is called hydraulic system heating. The characteristic of its malfunction is that during the cold car operation of the excavator, various movements are relatively normal. After about an hour of mechanical operation, with the increase of hydraulic oil temperature, the various actuators of the excavator become weak and the movements are slow, especially the excavation force is not strong, and the walking and turning are difficult.

If the hydraulic system of the Komatsu excavator repair shows a heating phenomenon and cannot be dealt with in a timely manner, it will have extremely adverse effects on the system:

(1) The viscosity of the oil decreases, leakage and addition cause the system to heat up, forming a vicious cycle;

(2) Accelerate oil oxidation, form gel like substances, block small holes in components, cause hydraulic components to malfunction or get stuck, and prevent operation;

(3) Aging and failure of rubber seals and hoses;

(4) Make the wear and tear of the oil pump and hydraulic valve components worse, and even render them useless.

2. Example analysis of repairing the hydraulic system heating problem of Komatsu excavator

For such problems, generally speaking, the repair of Komatsu excavator should start from the internal analysis of the hydraulic system. The primary internal reason is the unreasonable system design. Factors such as unreasonable matching between components, narrow pipeline channels, multiple bends, small radius of curvature, and insufficient fuel tank capacity are formed. This type of problem should be fully considered during the design phase, otherwise it will result in an inherent lack of hydraulic system in the excavator, which will be difficult to overcome after the product is made.

2.1 Heating of hydraulic system caused by external factors

The engine of the hydraulic pump for the Komatsu PC200-5 excavator is connected through a shock absorber in the shock absorber box. When dealing with the heating problem of the hydraulic system of an excavator, it was found that the oil level in the shock absorber box greatly exceeded the screw at the investigation oil level (usually about 1.5L). During the rolling process with the shock absorber damper, this excessive oil generated a lot of heat and transferred it to the hydraulic pump, causing the system to heat up.

At this moment, after repairing the Komatsu excavator and draining the shock absorber oil to the standard level, the problem can be eliminated. There are two reasons for the high oil level in the shock absorber box: firstly, the operator blindly refills the oil; The second issue is the aging of the oil seal at the shaft end of the hydraulic pump, which causes hydraulic oil to leak. In the latter case, the hydraulic pump should be disassembled to replace the oil seal.

2.2 Poor heat dissipation function of radiator causes high oil temperature

The primary forms of poor heat dissipation function of radiators are: deformation or blockage of external heat dissipation fins, resulting in poor cooling effect; Lack of cooling fan capacity; The internal pipeline of the hydraulic oil radiator is blocked. In addition to being visually distinguishable, the first two can also be determined from the small temperature difference between the upper and lower pipes of the radiator. At this moment, it is necessary to tidy up the heat sink and tighten the fan belt. The identification of internal pipeline blockage in hydraulic oil radiators can be achieved by installing pressure gauges in the inlet and outlet oil passages of the radiator to check the pressure difference between the two. If the oil temperature is around 45oC and the pressure difference is below 0.12MPa, it is considered normal. If it is higher than 0.12MPa, it indicates severe oil pipe blockage and the upper and lower covers of the radiator should be removed to clear the pipeline.

2.3 Hydraulic return oil filter one-way valve failure causes hydraulic oil overheating

From the hydraulic system schematic, it can be seen that the one-way valve of the hydraulic system return oil filter element is connected to the hydraulic oil radiator in parallel at the outlet of the return oil filter element (see PC200-5 hydraulic system schematic). Its function is to actively open when the pressure difference of the return oil radiator is above 0.185MPa, and short-circuit the radiator to form a return oil passage. In practical operations, due to the valve device being located at the bottom of the return oil filter element, it is difficult to inspect and maintain. In addition, a single operator's improper selection of hydraulic oil quality, long-term failure to change oil, and long-term disrepair have resulted in severe oil pollution, causing the valve to get stuck in the normally open position (some even privately remove the valve). Therefore, the return oil radiator does not have a heat dissipation effect, which inevitably leads to high oil temperature. Check if the valve is stuck during each replacement of hydraulic oil.

2.4 Improper selection of hydraulic oil trademark or poor oil quality causing high oil temperature

In recent years, the repair of Komatsu excavators has been caused by the use of non compliant or counterfeit oil, resulting in an increase in hydraulic system oil temperature. For example, misuse of oil with high viscosity can cause excessive loss of fluid pressure, which is converted into heat energy and can lead to excessive temperature rise; Misuse of hydraulic oil with low viscosity can also cause significant leakage and heat generation in hydraulic pumps and components during operation; In addition, some low-quality fluids have poor viscosity and temperature function, are prone to emulsification and produce cavitation, and may break bubbles, which can cause local high temperatures and increase component wear when hydraulic oil is under high pressure.

2.5 System heating caused by improper adjustment of pressure valves in pumps and hydraulic systems

The repair hydraulic pump of Komatsu excavator serves as the power source for the hydraulic system, and its working condition affects the degree of heating in the system. If the main pump of the PC200 excavator is a plunger pump, and there is significant wear between the distribution plate and the cylinder body, sliding shoes, inclined plate, and plunger cylinder body in the pump, it often leads to rapid heating of the hydraulic pump. This can be determined by investigating the fast heating and noise characteristics of the pump. Its revision

The PC200 excavator pilot control pump is a gear pump, which provides the system with operational control pressure oil and adjusts the main pump displacement according to load requirements. If the gear end face of the pump is worn or the tooth clearance is large, internal leakage and addition will cause the pump to heat up and affect the normal operation of the main pump.

Excessive or insufficient pressure of the overflow valve can also cause the hydraulic system to heat up. If the system pressure is adjusted too high during the repair of the Komatsu excavator, the hydraulic pump will operate beyond the rated pressure, causing the pump to overload and leading to an increase in oil temperature; On the contrary, if the system pressure regulation is too low, it will cause the operating mechanism to frequently exhibit the phenomenon of overflow valve opening and unloading under normal load, resulting in hydraulic system overflow heating.