08-24-2025, 03:15 PM
Machine Overview
The Sennebogen 825 is a robust material handler designed for heavy-duty scrap, recycling, and timber handling. With an operating weight around 28,800 kg (63,500 lbs), it features advanced hydraulic systems, a compact boom, and a hydraulically elevating cab for operator comfort and visibility. The grab attachment is central to efficient material manipulation, combining powerful gripping with precise control.
Problem Description
The reported issue involves insufficient hydraulic power when closing the grab, resulting in weak gripping and pressing of material. During a pressure test, the expected back pressure of approximately 250 bar was found to be only 110 bar during the grab closing function, indicating hydraulic pressure is bypassing somewhere in the system. Notably, during opening, pressure readings were normal at 250 bar.
Additionally, when the grab is opened and the control lever released, the cylinders drift quickly, causing the grab to close unintentionally. Despite replacing the grab cylinders with new ones, the problem of "loss of power" persists, suggesting the fault lies outside the cylinders themselves.
Possible Causes
Operators of scrap handling Sennebogen equipment have faced similar pressure loss issues where a cracked control valve spool was found to cause pressure bypass. Timely valve overhaul restored full grip strength and eliminated cylinder drift, avoiding costly downtime.
Another case involved a mis-routed hydraulic hose post-maintenance causing unintended flow between supply and return lines, leading to pressure loss during closing but normal opening pressure.
Final Thoughts
Hydraulic power loss in Sennebogen 825 grab closing typically originates in leaks or faults within the valve block or hydraulic circuitry rather than the cylinders themselves. Systematic hydraulic testing including back-pressure verification, valve inspections, and line integrity checks is essential to pinpoint and remedy the problem. Resolving such issues ensures optimal grab force, operational efficiency, and safety for heavy material handling applications.
The Sennebogen 825 is a robust material handler designed for heavy-duty scrap, recycling, and timber handling. With an operating weight around 28,800 kg (63,500 lbs), it features advanced hydraulic systems, a compact boom, and a hydraulically elevating cab for operator comfort and visibility. The grab attachment is central to efficient material manipulation, combining powerful gripping with precise control.
Problem Description
The reported issue involves insufficient hydraulic power when closing the grab, resulting in weak gripping and pressing of material. During a pressure test, the expected back pressure of approximately 250 bar was found to be only 110 bar during the grab closing function, indicating hydraulic pressure is bypassing somewhere in the system. Notably, during opening, pressure readings were normal at 250 bar.
Additionally, when the grab is opened and the control lever released, the cylinders drift quickly, causing the grab to close unintentionally. Despite replacing the grab cylinders with new ones, the problem of "loss of power" persists, suggesting the fault lies outside the cylinders themselves.
Possible Causes
- Hydraulic Valve Leak or Fault: Internal leakage within directional control valves or spool valves can cause pressure bypassing specifically when closing the grab. This would reduce pressure build-up during closing but not during opening.
- Hydraulic Line Leak or Improper Routing: Pressure bypass may occur due to worn seals or damaged hoses allowing flow to leak back to the tank or unintended circuit paths.
- Back Pressure Valve or Check Valve Malfunction: Valves designed to hold pressure in the closing line may fail, allowing fluid to return prematurely and causing cylinder drift.
- Hydraulic Pump or Accumulator Issues: Insufficient flow or pressure from the pump or faulty accumulators can reduce pressure delivery under load, though this would likely affect both opening and closing.
- Control Lever or Servo Cylinder Defects: Malfunctioning servo actuators or linkage in the control signals may cause improper pressure modulation.
- Back Pressure: Hydraulic pressure that resists flow in a line, necessary for proper force generation.
- Directional Control Valve: Valve used to control flow direction to actuators like cylinders.
- Cylinder Drift: Unintended movement of a hydraulic cylinder when control input is removed, often due to seal failure or valve leakage.
- Hydraulic Accumulator: Pressure storage device using gas and fluid separation to maintain system stability.
- Perform detailed inspection and testing of hydraulic valves controlling grab closing for internal leakage and seal integrity.
- Pressure test hydraulic lines and hoses connected to the grab circuit for leaks, bulges, or damage.
- Check and replace or repair back pressure valves or check valves ensuring proper non-return function.
- Verify hydraulic pump capacity and pressure output consistency under varying loads.
- Inspect control levers, servo systems, and electrical controls for reliability and calibration.
- Since cylinder replacement did not resolve drifting, focus on valve block or hose diagnostics.
Operators of scrap handling Sennebogen equipment have faced similar pressure loss issues where a cracked control valve spool was found to cause pressure bypass. Timely valve overhaul restored full grip strength and eliminated cylinder drift, avoiding costly downtime.
Another case involved a mis-routed hydraulic hose post-maintenance causing unintended flow between supply and return lines, leading to pressure loss during closing but normal opening pressure.
Final Thoughts
Hydraulic power loss in Sennebogen 825 grab closing typically originates in leaks or faults within the valve block or hydraulic circuitry rather than the cylinders themselves. Systematic hydraulic testing including back-pressure verification, valve inspections, and line integrity checks is essential to pinpoint and remedy the problem. Resolving such issues ensures optimal grab force, operational efficiency, and safety for heavy material handling applications.
