Fault analysis of hydraulic system heating in Caterpillar excavator

The heating phenomenon and hazards of the hydraulic system of the CAT 336 excavator. Hydraulic system heating is a common and complex soft fault in excavator operation. Under normal working conditions, the hydraulic system oil temperature of the Komatsu PC200/400 excavator should be below 60oC (the temperature of the oil pump is 5-10oC higher). If it exceeds the limit, it is called hydraulic system heating. Its fault characteristics are: when the excavator is working cold, various actions are normal. After about an hour of mechanical operation, as the hydraulic oil temperature rises, various actuators of the excavator become weak and slow to move, especially when the excavation force is insufficient and the walking and turning are difficult. If the heating phenomenon of the hydraulic system cannot be dealt with in a timely manner, it will affect the system. Extremely adverse effects:

(1) The viscosity of the oil decreases, the leakage increases, and the system heats 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 fail to work;

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

(4) Intensify the wear and tear of the oil pump and hydraulic valve components, and even render them unusable.

Example analysis of heating faults in hydraulic systems of excavators. Generally speaking, for such faults, the first step should be to start with the internal analysis of the hydraulic system. The internal reasons are mainly caused by unreasonable system design, such as unreasonable matching between components, narrow pipeline channels, many bends, small bending radii, and insufficient oil tank capacity. These problems should be fully considered in the design stage, otherwise it will cause inherent deficiencies in the hydraulic system of excavators, which will be difficult to overcome after the product is made,

2.1 Hydraulic system heating caused by external factors. For example, the engine of the hydraulic pump in the Caterpillar 336D used excavator is connected through a shock absorber damper in the shock absorber box. When dealing with a hydraulic system heating fault in an excavator, it was found that the oil level in the shock absorber box was much higher than the screw at the observation oil level (usually about 1.5L). During the rotation of the shock absorber damper, this excess oil generated a large amount of heat and transferred it to the hydraulic pump, causing the system to heat up. At this time, the fault can be eliminated by draining the shock absorber box oil to the standard oil level. There are two reasons for the high oil level in the shock absorber box: one is that the operator blindly refuels; The second issue is the aging of the oil seal at the shaft end of the hydraulic pump, which leads to leakage of hydraulic oil. The latter requires dismantling the hydraulic pump and replacing the oil seal,

2.2 Poor heat dissipation performance of radiators can cause high oil temperatures. The main forms of poor heat dissipation performance of radiators are: deformation or blockage of external heat dissipation fins, poor cooling effect; Insufficient cooling fan capacity; The internal pipeline of the hydraulic oil radiator is blocked. In addition to visually judging the first two, it can also be inferred from the small temperature difference between the upper and lower pipes of the radiator. At this time, the heat sink should be cleaned, and the fan belt should be tightened. To determine the blockage of the internal pipeline of the hydraulic oil radiator, a pressure gauge can be installed in the inlet and outlet oil passages of the radiator to check the pressure difference between the two. If the oil temperature is around 45 degrees and the pressure difference is below 0.12MPa, it is normal. If it is higher than 0.12MPa, it indicates that the oil pipe is severely blocked. 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 hydraulic system return oil filter one-way valve is connected to the hydraulic oil radiator and is connected to the outlet of the return oil filter. Its function is to automatically open when the pressure difference of the return oil radiator is above 0.185MPa, short circuiting the radiator to form a return oil passage. In actual operation, because the valve is installed at the bottom of the return oil filter, it is difficult to inspect and maintain. In addition, some operators have improper selection of hydraulic oil quality, long-term oil replacement and long-term disrepair, which causes serious oil pollution, resulting in the valve being stuck in the normally open position (some even dismantle the valve without authorization). Therefore, the return oil radiator does not have a heat dissipation effect, which will inevitably cause high oil temperature. When replacing hydraulic oil, check if this valve is stuck,

2.4 Improper selection of hydraulic oil grades or poor oil quality leading to high oil temperature. In recent years, there have been multiple failures in hydraulic system oil temperature caused by the use of oil with non compliant performance or counterfeit oil. For example, misuse of oil with high viscosity can cause excessive loss of fluid flow pressure, which can be converted into thermal energy and cause high temperature rise; Misuse of hydraulic oil with low viscosity can also cause large leaks in the working hydraulic pump and hydraulic components, generating heat; In addition, some low-quality fluids have poor viscosity and temperature performance, are prone to emulsification and production cavitation, and produce bubbles, which can generate local high temperatures under high hydraulic oil pressure and exacerbate component wear,

2.5 System heating caused by improper adjustment of pump and hydraulic system pressure valve. As the power source of the hydraulic system, the working condition of the hydraulic pump affects the degree of system heating. For example, the main pump of PC200 excavator is a plunger pump. If the fitting position between the distribution plate and the cylinder body, sliding shoe, inclined plate and plunger cylinder body in the pump is worn out, it often causes the hydraulic pump to heat up quickly. This can be judged by observing the characteristics of the pump heating up quickly and having noise. The repair method is to grind and repair the relevant sealing fitting surface or replace irreparable parts. PC200 The pilot control pump of the excavator is a gear pump, which provides operation control pressure oil for the system and adjusts the displacement of the main pump according to the load requirements. If the gear end face of the pump is worn or the tooth clearance is large, the internal leakage will increase, which will cause the pump to heat up and affect the normal operation of the main pump. If the pressure of the relief valve is too high or too low, it will also cause the hydraulic system to heat up. If the system pressure is adjusted too high, it will cause the hydraulic pump to operate at a pressure exceeding the rated pressure, overload the pump, and lead to an increase in oil temperature; On the contrary, if the system pressure regulation is too low, it will cause the working mechanism to frequently experience the phenomenon of overflow valve opening and unloading under normal load, resulting in hydraulic system overflow and heating. The set values of each pressure valve in the hydraulic system of the Komatsu PC200-5 excavator are listed in the table below. The standard values of the test conditions (Mpa) for the test parts are noted as the main overflow valve oil temperature of about 45oC, 32.5 (+0.8-1.1) for the two sets of boom engines, high idle speed of 32.5 (+0.8-1.1) for the boom main pump outlet, 32.5 (+0.8-1.1) for the bucket, 29.0 (+1-0.5) for rotation, 32.5 (+0.8-1.1) for walking, 32.5 (+0.8-1.1) for pilot control pump oil temperature of about 45oC, and 3.2 (+0.4-0.1) for the pilot control pump. TVC control valve operating stem neutral 2.0 (+0.1-0.1)

https://www.lh-usedexcavator.com/