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Methods for Addressing Abnormally High Hydraulic Oil Temperature in Rock Drilling Rigs
Release time:
2026-11-18
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Summary:
The hydraulic system of a rock drilling rig should maintain an operating oil temperature between 30 and 70°C. If the temperature exceeds 70°C, travel or operation must be stopped immediately, and normal operation may resume only after the oil temperature has returned to the acceptable range. Failure to address abnormally high oil temperatures promptly can accelerate fluid oxidation, reduce viscosity, and increase component wear, creating a vicious cycle. When troubleshooting, follow the sequence of cooling first, then diagnosing, and finally repairing, progressing layer by layer from external heat dissipation conditions to internal system faults.
I. Emergency Cooling and Safe Shutdown
If the oil temperature exceeds 70°C, first stop the trolley, retract the boom to a safe position, and let the engine idle. Do not shut off the engine immediately, as idling allows hydraulic oil to circulate slowly through the system, aiding heat transfer to the radiator. At the same time, check that the oil level in the tank is within the normal range; insufficient oil will directly reduce cooling capacity. If the oil temperature continues to rise and is accompanied by unusual noises or abnormal operation, shut down the engine and contact maintenance personnel.
II. Investigation of External Heat Dissipation Conditions
Radiator blockage is a common external cause of rising oil temperatures. When rock drilling rigs operate underground, dust and rock powder can easily clog the radiator fins, reducing cooling efficiency. To address this, use compressed air to blow backward through the fins from the rear of the radiator, removing accumulated dust; if oil deposits are thick, rinse with low-pressure water and then blow dry. Routine maintenance should include cleaning the fins at each shift and inspecting fan operation weekly.
The fan drive system also requires inspection. For hydraulically motor‑driven fans, check for oil leaks and verify that the rotational speed is normal; for electrically motor‑driven fans, inspect the motor for moisture or poor wiring connections. With water‑cooled radiators, ensure that the cooling water flow is adequate. If scale builds up inside the cooler due to hard water, heat transfer efficiency will be significantly reduced, so scale should be removed regularly.
To determine whether the radiator is internally blocked, use an infrared thermometer to measure the temperature difference between the oil inlet and outlet. If the temperature difference is very small, it indicates that the oil is exiting the radiator without being effectively cooled. Alternatively, install pressure gauges at the radiator’s inlet and outlet; with the oil temperature around 45°C, the pressure drop should be below 0.12 MPa. Exceeding this value suggests severe internal blockage of the oil passages, requiring disassembly and cleaning.
III. Internal Fault Diagnosis of the Hydraulic System
If the external cooling conditions are normal but the oil temperature remains high, the focus should be on troubleshooting internal system issues.
Faults in the backpressure valve and the bypass valve. The bypass valve opens when radiator pressure becomes too high, allowing some oil to return directly to the tank without passing through the radiator. If the bypass valve remains constantly open or the backpressure valve is stuck closed, hydraulic oil will bypass the cooling circuit and flow straight back to the tank, causing the oil temperature to rise. The operating status and set pressures of both valves should be checked.
Internal leakage within the system. Excessive clearance between the spool and valve bore in a multi-way valve, excessive clearance between the hydraulic pump piston and cylinder block, or worn seals in the hydraulic cylinder can all cause high-pressure oil to leak to the low-pressure side. The leaked hydraulic fluid converts pressure energy into heat, directly heating the system. A practical method for diagnosing internal leakage is to measure, using an infrared thermometer, the temperature difference between the hydraulic pump housing and the outlet oil temperature. If the housing temperature exceeds the outlet oil temperature by 5–10°C, it indicates significant mechanical wear but the pump is still serviceable; a temperature difference greater than 10°C suggests severe wear, increased axial clearance, and the need for repair or replacement.
The relief valve is malfunctioning. When the set pressure of the relief valve is too low, the system frequently overflows and unloads under normal load, causing a large volume of hydraulic oil to return to the tank through the relief valve, with the absorbed power converted into heat. If the relief valve spool is stuck or internal leakage is excessive, the valve body temperature will rise abnormally. Under normal conditions, the valve housing temperature is about 30°C higher than the ambient room temperature; if it exceeds this by more than 40°C, the cause may be a stuck spool or excessive internal leakage.
Indirect effects of hydraulic–water system interaction. The water circuit of a rock drilling rig is linked to its hydraulic system. If the water‑to‑air control valve fails to operate or water pressure is insufficient, cutting off the water supply will not stop drilling, potentially causing bit jamming. When the rotary motor becomes obstructed, oil pressure rises sharply; if the anti‑jamming valve does not relieve pressure and return oil promptly, oil temperature will increase. Therefore, when troubleshooting oil temperature issues, it is also necessary to verify that the water system is functioning properly.
IV. Recovery and Prevention After Treatment
After troubleshooting, the hydraulic oil quality should be checked. Prolonged elevated oil temperatures accelerate oxidation; if the oil darkens in color, develops an unusual odor, or exhibits a noticeable change in viscosity, the hydraulic oil should be replaced and the system lines and filter elements cleaned. During routine maintenance, keeping the radiator clean, periodically inspecting the backpressure valve and bypass valve, monitoring changes in the hydraulic pump housing temperature, and selecting hydraulic oil with appropriate viscosity for the season are standard practices to reduce the likelihood of abnormal oil temperatures.
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