SANY SR280 Slow Main Winch Pilot Pressure Diagnosis

A slow main winch can tempt a repair team to suspect the motor, gearbox, or main valve first. Those components are expensive and difficult to replace, but the same symptom can appear when the pilot circuit does not move the main spool far enough. The most efficient diagnosis therefore starts with measured pressure and follows the control path from the operator command to the main hydraulic flow.

This field report concerns an SR280 in Guangzhou whose main winch was slow while lifting and lowering. The technicians measured the main-winch ports, checked brake-release pressure and gearbox behavior, and then moved upstream through the pilot circuit. The final result connected low pilot pressure to the pilot relief-valve setting and verified the correction with both pressure and line-speed measurements.

The Main Winch Was Slow While Lifting and Lowering

The complaint affected both directions of the main winch. That pattern was important because it did not point immediately to a single-direction check valve or one isolated command. The team considered insufficient main pressure, internal motor leakage, gearbox damage, a sticking main-winch spool, and inadequate pilot pressure.

The pilot path runs through the pilot pump, pilot control valve, hand controller, solenoid valve group, and main control valve. Main flow then travels through the main-winch valve section to the motor. Testing these stages in order prevented a control-pressure problem from being confused with a major component failure.

Symptom: slow main-winch movement in both lifting and lowering directions.
Machine identified in the report: SANY SR280.
Field location stated in the report: Guangzhou.
Initial fault groups: main circuit, motor, gearbox, main valve, and pilot circuit.

Main Pressure and Brake Release Were Checked Before Major Parts

Pressure gauges were connected to the relevant main-winch motor ports and brake-release circuit. The report records 34 MPa while lifting, 20 MPa while lowering, and 2.8 MPa at the brake-release circuit. These values were treated as normal for the test condition in the source report.

The winch brake was then released and the winch operated while the gearbox was observed. No abnormal gearbox noise was recorded. These checks reduced concern about insufficient main pressure, failed brake release, or an obvious gearbox failure.

Recorded lifting pressure: 34 MPa.
Recorded lowering pressure: 20 MPa.
Recorded brake-release pressure: 2.8 MPa.
Gearbox check: no abnormal noise recorded during operation.

Main winch motor and valve assembly inspected during pressure diagnosis

A 2.7 MPa Pilot Reading Revealed the Control-Side Shortfall

The technicians next measured pilot pressure at the main-winch control circuit. The gauge showed 2.7 MPa, below the 3.8 to 4 MPa range stated in the field report. Low pilot pressure can prevent the main spool from reaching the commanded position even when the main pump can generate adequate pressure.

To determine whether the loss occurred downstream or began at the source, the team measured pressure at the pilot-pump outlet. It was 2.8 MPa, confirming that the low reading was already present before the pilot flow reached the controller and main valve.

This upstream comparison was the decisive test. It connected the slow winch response to the pilot supply instead of the main-winch motor. The supplied field photographs document the main-winch motor and valve assembly and the main control valve examined in the system.

Main-winch pilot pressure: 2.7 MPa.
Expected range stated by the source report: 3.8 to 4 MPa.
Pilot-pump outlet pressure: 2.8 MPa.
Diagnostic conclusion: the pressure shortfall originated in the pilot supply.

Rotary drilling rig main control valve examined during a slow-winch diagnosis

Pressure and Winch Speed Confirmed the Corrective Action

The report attributes the low opening pressure to a softened regulating spring in the pilot relief valve. Under the recorded service procedure, the relief-valve locknut was loosened, the adjustment was increased by one-half turn, and the locknut was secured again.

After adjustment, pilot-pump outlet pressure measured 3.9 MPa. The winch was operated again, and its movement was visibly faster. The report records a lifting speed of 49 m/min and a lowering speed of 59 m/min after the correction.

These numbers are case evidence, not universal adjustment targets. Relief settings, test ports, oil temperature, engine speed, load condition, and allowable winch speed must follow the service information for the exact machine. The useful method is to measure before adjustment and confirm both pressure and function afterward.

Corrective action: adjust and relock the pilot relief valve under the source procedure.
Verified pilot-pump outlet pressure after adjustment: 3.9 MPa.
Verified lifting speed after adjustment: 49 m/min.
Verified lowering speed after adjustment: 59 m/min.

What an Overseas Buyer Should Request in a Main-Winch Test

Ask for the main winch to be demonstrated in both directions through a controlled operating range. The video should show engine speed, load condition, drum movement, brake release, control response, and any abnormal noise. A fast unloaded drum alone does not establish performance under the machine's applicable test condition.

Request the actual pressure readings used to diagnose a slow winch. The record should identify the test point, gauge range, oil temperature, engine speed, command direction, and whether the measurement was taken under stall, load, or free-running conditions.

Test lifting and lowering under controlled, documented conditions.
Record main pressure, brake-release pressure, and pilot pressure at identified test points.
Listen for gearbox noise and inspect the drum, rope, and brake behavior.
Require post-repair pressure and speed evidence before shipment.

Measure Before Replacing Major Components

The slow SR280 main winch was not traced to inadequate main pressure, failed brake release, or obvious gearbox damage. A 2.7 MPa pilot reading and a 2.8 MPa pilot-pump outlet reading moved the diagnosis to the pilot relief circuit.

After the recorded relief-valve correction, outlet pressure reached 3.9 MPa and the winch achieved 49 m/min lifting and 59 m/min lowering. For a used-equipment buyer, that measured before-and-after chain provides stronger evidence than replacing a motor or gearbox without first isolating the control pressure.

Safety Note

Hydraulic pressure testing and relief-valve adjustment can cause uncontrolled machine movement, hose failure, fluid injection, or load drop. Only qualified personnel should perform this work using calibrated gauges, the exact machine service procedure, approved test points, correct oil-temperature and engine-speed conditions, secure load control, and an exclusion zone. Never copy the adjustment amount or pressure values to another machine without its verified specification.