Analysis of Five Reasons for Heating in the Hydraulic System of Komatsu PC200 Excavator
For such faults, it is generally recommended to start with an internal analysis of the hydraulic system from the outside. The internal reasons are mainly caused by unreasonable system design. Due to factors such as unreasonable matching between components, narrow pipeline channels, multiple bends, small bending radii, and insufficient fuel tank capacity. Such issues should be fully considered during the design phase, otherwise it will result in inherent deficiencies in the hydraulic system of the excavator, which will be difficult to overcome once the product is manufactured.
(1) Heating of hydraulic system caused by external factors
The engine of the hydraulic pump for the Komatsu PC200 excavator is connected through a shock absorber damper inside 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 significantly higher than the screw at the observed oil level (usually about 1.5l). This excess oil generated a large amount of heat during the rotation of the shock absorber damper and transferred it to the hydraulic pump, causing the system to heat up.
At this point, the fault can be eliminated by draining the shock absorber oil to the standard level. 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 leakage of hydraulic oil. The latter should be replaced by removing the hydraulic pump plug and replacing the oil seal.
(2) Poor heat dissipation performance of radiator causes high oil temperature
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 intuitive judgment, the first two can also be inferred from the small temperature difference between the upper and lower pipes of the radiator. At this time, it is necessary to clean the heat sink and tighten the fan belt. The determination of internal pipeline blockage in hydraulic oil radiators can be made by installing pressure gauges in the inlet and outlet oil passages of the radiator and checking the pressure difference between the two. If the oil temperature is around 45 ° C and the pressure difference is below 0.12 MPa, it is considered normal. If it is higher than 0.12 MPa, it indicates severe oil pipe blockage and the upper and lower covers of the radiator should be removed to clear the pipeline.
(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 outlet of the return oil filter element in parallel with the hydraulic oil radiator. Its function is to automatically open when the pressure difference of the return oil radiator is above 0.185mpa, and short-circuit the radiator to form the return oil passage. In practical work, due to the installation of the valve at the bottom of the return oil filter element, it is difficult to inspect and maintain. In addition, some operators have improper selection of hydraulic oil quality, long-term failure to change oil, and long-term disrepair, which have caused serious oil pollution. As a result, the valve is stuck in the normally open position (some even remove it without authorization), and the return oil radiator does not have a heat dissipation effect, inevitably leading to high oil temperature. Check for any sticking of this valve every time the hydraulic oil is replaced.
(4) Improper selection of hydraulic oil grade or poor oil quality causing high oil temperature
In recent years, there have been multiple incidents of hydraulic system oil temperature rise due to the use of non compliant or counterfeit oil. For example, misusing oil with high viscosity can cause excessive pressure loss in the fluid flow, which is converted into heat energy and can lead to excessive 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 cavitation during production, and produce bubbles, which can generate local high temperatures under high hydraulic oil pressure and exacerbate component wear.
(5) System heating caused by improper adjustment of pressure valves in pumps and hydraulic systems
As the power source of the hydraulic system, the working condition of the hydraulic pump affects the degree of system heating. If the main pump of the PC200 excavator is a plunger pump, if the fitting position between the distribution plate and the cylinder body, sliding shoes, inclined plates, 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 rapid heating and noise characteristics of the pump. The repair method is to grind and repair the sealing mating surface or replace parts that cannot be repaired.
The pilot control pump of PC200 excavator is a gear pump, which provides operation control pressure oil for the system and adjusts the displacement of the main pump according to 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.
Excessive or insufficient pressure of the relief valve can also cause the hydraulic system to heat up. If the system pressure is adjusted too high, it can cause the hydraulic pump to operate beyond its rated pressure, overload the pump, and lead to an increase in oil temperature; On the contrary, if the system pressure regulation is too low, the working mechanism will frequently experience the phenomenon of overflow valve opening and unloading under normal load, causing hydraulic system overflow and heating.
The heating phenomenon of hydraulic system and its hazards. Hydraulic system heating is a common fault phenomenon in excavators, and it is also a complex soft fault to analyze and deal with. Under normal operating conditions, the hydraulic system oil temperature of the Komatsu PC200/400 excavator should be below 60 o C (the temperature of the oil pump should be 5-10 o C higher). If it exceeds this limit significantly, it is called hydraulic system heating. The 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, the excavator's various actuators become weak and slow in action, especially when the excavation force is insufficient and the walking and turning are difficult. If the heating phenomenon in the hydraulic system cannot be dealt with in a timely manner, it will have extremely adverse effects on the system:
(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 hydraulic system heating faults in excavators. Generally speaking, for such faults, the first step should be to start with an external internal analysis of the hydraulic system. The internal reasons are mainly caused by unreasonable system design. Due to factors such as unreasonable matching between components, narrow pipeline channels, multiple bends, small bending radii, and insufficient fuel tank capacity. Such issues should be fully considered during the design phase, otherwise it will result in inherent deficiencies in the hydraulic system of the excavator, which will be difficult to overcome once the product is manufactured.
2.1 Hydraulic system heating caused by external factors, such as the engine of the Komatsu PC200 excavator hydraulic pump, is connected through a shock absorber damper inside 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 significantly higher than the screw at the observed oil level (usually about 1.5L). This excess oil generated a large amount of heat during the rotation of the shock absorber damper and transferred it to the hydraulic pump, causing the system to heat up. At this point, the fault can be eliminated by draining the shock absorber oil to the standard level. 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 leakage of hydraulic oil. The latter should be replaced by removing the hydraulic pump plug 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 intuitive judgment, the first two can also be inferred from the small temperature difference between the upper and lower pipes of the radiator. At this time, it is necessary to clean the heat sink and tighten the fan belt. The determination of internal pipeline blockage in hydraulic oil radiators can be made by installing pressure gauges in the inlet and outlet oil passages of the radiator and checking the pressure difference between the two. If the oil temperature is around 45 o C 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 hydraulic system return oil filter one-way valve is connected to the outlet of the return oil filter in parallel with the hydraulic oil radiator. Its function is to automatically open when the pressure difference of the return oil radiator is above 0.185MPa, and short-circuit the radiator to form the return oil passage. In practical work, due to the installation of the valve at the bottom of the return oil filter element, it is difficult to inspect and maintain. In addition, some operators have improper selection of hydraulic oil quality, long-term failure to change oil, and long-term disrepair, which have caused serious oil pollution. As a result, the valve is stuck in the normally open position (some even remove it without authorization), and the return oil radiator does not have a heat dissipation effect, inevitably leading to high oil temperature. Check for any sticking of this valve every time the hydraulic oil is replaced.
2.4 Improper selection of hydraulic oil grades or poor oil quality leading to high oil temperature. In recent years, multiple faults have occurred due to the use of non compliant or inferior oil, resulting in an increase in hydraulic system oil temperature. For example, misusing oil with high viscosity can cause excessive pressure loss in the fluid flow, which is converted into heat energy and can lead to excessive 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 cavitation during production, and produce bubbles, which can generate local high temperatures under high hydraulic oil pressure and exacerbate component wear.
Improper adjustment of pump and hydraulic system pressure valve can cause system heating. As the power source of the hydraulic system, the working condition of the hydraulic pump affects the degree of system heating. If the main pump of the PC200 excavator is a plunger pump, if the fitting position between the distribution plate and the cylinder body, sliding shoes, inclined plates, 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 rapid heating and noise characteristics of the pump. The repair method is to grind and repair the sealing mating surface or replace parts that cannot be repaired. The PC200 excavator pilot control pump is a gear pump, which provides operation control pressure oil for the system and adjusts the displacement of the main pump according to 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. Excessive or insufficient pressure of the relief valve can also cause the hydraulic system to heat up. If the system pressure is adjusted too high, it can cause the hydraulic pump to operate beyond its 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 heating
