SANY SR150 Engine Running but the Machine Would Not Move: Diagnosing a Worn Pump Coupling

When a rotary drilling rig's engine is running but every hydraulic function has stopped, the fault can look larger than it is. The operator may suspect the controller, pilot system, several pumps, or a major hydraulic failure. In this field case, a 2009 SANY SR150 suddenly lost all machine and mast movement during work even though the engine was running normally.

The failure affected both pilot-controlled functions and mast adjustment. The technicians checked the pilot command, reviewed pressure indications, and confirmed delivery at pump outlets. The evidence made simultaneous pump failures unlikely and directed the inspection toward the mechanical drive between the engine and pumps.

This article is adapted from the supplied repair report. It retains the documented model, year, measurements, confirmed component damage, and repair result while removing personal and internal service information.

A Complete Loss of Functions with a Healthy Engine

The SR150 was working when all machine functions stopped suddenly. Moving the operating joysticks produced no response, and the mast-adjustment control also produced no movement. The engine continued to run normally.

This pattern differed from a failure limited to the pilot-control circuit. If mast adjustment remained available, the pilot solenoid or pilot oil path would deserve greater priority. Here, complete loss of movement indicated that hydraulic power might not be reaching the systems.

• Machine identified in the source: 2009 SANY SR150.
• Failure occurred suddenly during operation.
• Joysticks and mast-adjustment control produced no movement.
• The engine continued to run normally.

Confirm the Command Before Condemning the Pumps

The service team first considered four areas: the engine-to-pump coupling, the hydraulic-pump input shaft, the pilot pump, and the pilot solenoid or its electrical supply. Each could contribute to a no-movement complaint, but they would not all produce the same supporting evidence.

With the pilot control enabled, a multimeter confirmed that the pilot solenoid received power. A small screwdriver placed near the energized solenoid was attracted magnetically, showing that the coil was active. This check did not prove that the entire pilot hydraulic circuit was healthy, but it showed that the electrical command was present and that the solenoid coil was responding.

• Verify whether the mast can still move before classifying a total no-function fault.
• Check pilot-solenoid supply rather than assuming that the controller has stopped issuing commands.
• Confirm coil magnetism as supporting evidence, not as the only hydraulic test.
• Continue to pressure and flow checks when every function remains unavailable.

Zero Pressure Across Multiple Circuits Changed the Diagnosis

After starting the rig, the display showed main, auxiliary, and pilot pressure readings of 0 MPa. The machine was then stopped and the pilot-pump outlet was opened for a controlled delivery check. After restart, no pressure oil emerged. The auxiliary-pump outlet was checked in the same way and also produced no oil delivery.

A damaged pilot pump alone would not explain the absence of auxiliary-pump delivery. Simultaneous internal failure of the pilot and auxiliary pump sections was also considered unlikely. The common element was their mechanical power input. Because the engine was operating but the pumps were not producing pressure or flow, the engine-to-pump drive became the leading suspect.

• Main hydraulic pressure shown on the display: 0 MPa.
• Auxiliary hydraulic pressure shown on the display: 0 MPa.
• Pilot hydraulic pressure shown on the display: 0 MPa.
• Pilot and auxiliary pump outlet checks showed no oil delivery.

The Coupling Teeth Had Worn Smooth

The engine-to-hydraulic-pump coupling was removed for inspection. Its internal ring-gear teeth had been worn smooth, so the running engine could no longer transmit useful torque to the hydraulic pumps. This single mechanical failure explained why several hydraulic circuits lost pressure at the same time.

A serviceable coupling was installed. After reassembly, the rig restored normal operation. The repair result matched the diagnosis: renewing the mechanical connection returned power to the pump group without treating the pilot, auxiliary, and main circuits as unrelated failures.

• Confirmed root cause: worn-smooth internal teeth in the engine-to-pump coupling.
• Mechanical consequence: engine torque was not transmitted to the hydraulic pumps.
• Corrective action: replace the damaged coupling and reassemble the pump drive.
• Verification: the machine restored normal operation after replacement.

What This Failure Means During a Used-Rig Inspection

A running engine is not proof that a rotary drilling rig can develop hydraulic power. During inspection, ask to see mast movement, travel, rotation, main-winch operation, and pressure response after the machine reaches operating condition. A complete function test can reveal a weak or intermittent drive connection before shipment.

If a coupling has been replaced, request photographs of the failed teeth, the replacement component, alignment during installation, and the final pressure/function test. Also ask whether the pump input and surrounding mounts were inspected for secondary damage. Those records help distinguish a confirmed mechanical repair from a no-movement complaint that was cleared temporarily without identifying the cause.

Kepler Machinery uses this evidence-led approach when inspecting and preparing used equipment: confirm the symptom, test the electrical command, compare pressure and flow across related circuits, inspect the common mechanical path, and record the final operating result.

• Test every major hydraulic function with the engine at appropriate operating speed.
• Compare main, auxiliary, and pilot pressure evidence when all functions are lost.
• Request photographs of worn coupling teeth and the installed replacement.
• Verify normal operation after the machine is fully reassembled.

Use Shared Evidence to Find a Shared Cause

The SR150 fault was not solved by replacing several hydraulic components. A working pilot-solenoid command, 0 MPa readings across multiple circuits, and no delivery from separate pump outlets all pointed toward the shared mechanical drive. Inspection then confirmed that the coupling teeth had worn smooth.

For a used-equipment buyer, the value of this case lies in the diagnostic chain. The final photographs show the failed component, while the pressure and function checks explain why it was inspected. That combination makes the repair easier to evaluate than a parts list alone.

Safety Note

Hydraulic pressure tests, opened pump outlets, lifting of the pump group, and coupling replacement must be performed by qualified technicians. Stop and isolate the machine before loosening hydraulic connections, release stored pressure, use rated lifting equipment, prevent contamination, and follow the correct alignment and torque procedures during reassembly.