SANY SR280 Main Winch Running Slowly: Hydraulic Diagnosis and Repair
A SANY SR280 rotary drilling rig in Guangzhou, China developed a main-winch fault: both hoisting and lowering were noticeably slower than normal. Because several hydraulic and mechanical faults can produce the same symptom, the inspection followed the circuit step by step instead of replacing parts by assumption.
How the Main Winch Circuit Works
With the engine running, the main pump supplies the working circuit. The pilot circuit runs from the pilot pump through the PPC valve and the left-hand joystick, then through the 2D, 11D, and 14D solenoid valves to the main control valve. The main oil flow runs from the main pump through the main-winch section of the control valve to the winch motor.
Possible Causes Considered
- Insufficient hoisting or lowering pressure at the main-winch motor
- Excessive internal leakage in the main-winch motor
- A fault in the winch reduction gearbox
- A sticking spool in the main-winch section of the control valve
- Insufficient pilot pressure
Pressure Tests and Diagnosis
Pressure gauges were connected to the MA, MB, and Bre ports with the main winch braked. Hoisting relief pressure measured 34 MPa, lowering relief pressure measured 20 MPa, and brake-cylinder pressure measured 2.8 MPa. These readings were normal, so insufficient main-circuit and brake pressure could be ruled out.
The brake was then released and the winch operated. No abnormal sound came from the reduction gearbox, making a gearbox fault unlikely.
Pilot pressure during hoisting and lowering measured only 2.7 MPa, below the normal 3.8 to 4.0 MPa range. A further test at the pilot-pump outlet produced 2.8 MPa, confirming that the low pressure originated upstream of the joystick and main control valve.
Corrective Action
The locknut on the relief valve near the pilot pump was loosened, and the adjustment screw was turned inward by one-half turn. After the locknut was secured, pilot-pump outlet pressure measured 3.9 MPa and returned to the normal range. Hydraulic pressure adjustments must be carried out by qualified technicians using the applicable service data and calibrated test equipment.
Result
The main winch responded significantly faster after the adjustment. Verified hoisting speed was 49 m/min, and lowering speed was 59 m/min.
Root Cause and Inspection Takeaway
The pressure-regulating spring in the pilot-pump relief valve had weakened. This reduced the relief-valve opening pressure and pulled down pilot pressure across the system. The case shows why a slow winch should be diagnosed with pressure measurements in circuit order: the visible symptom was at the winch, but the fault source was the pilot-pressure supply.