10-19-2025, 01:58 PM
Boom Settling Is Normal Within Cylinder Drift Tolerance
The Yanmar VIO35-6 mini excavator is known for its compact zero-tail design and efficient hydraulic system, but some owners report that the boom slowly settles after the machine is shut down. This behavior is not necessarily a defect—it falls within the acceptable range of hydraulic cylinder drift defined by manufacturers. For the VIO35-6, settling of the boom over several hours or days is considered normal if it does not exceed specific tolerances.
Yanmar VIO35-6 Overview and Hydraulic Design
Yanmar introduced the VIO35-6 as part of its sixth-generation compact excavator lineup, targeting urban construction, landscaping, and utility work. With an operating weight of approximately 8,000 lbs and a 24.4 hp Tier IV Final diesel engine, the machine features a load-sensing hydraulic system and a variable displacement pump. The boom and arm cylinders are equipped with standard piston seals and check valves, but not all models include load-holding valves or pilot-operated check valves on the boom circuit.
Terminology Notes
When the engine is turned off, hydraulic pressure bleeds off through the control valve stack. If the boom is left raised, gravity acts on the cylinder, and any internal leakage past the piston seals or through the valve block allows the boom to slowly lower. This is especially noticeable in newer machines with tight tolerances, as the movement may be slow but still present.
Manufacturers typically allow up to 10 mm of cylinder movement per hour at operating temperature. Over several days, this can result in visible boom settling. Machines like older Kobelco or Kubota models may appear to hold position longer due to different valve configurations or tighter seal designs.
Preventive Practices and Operator Advice
A rental fleet manager in Illinois noted that his VIO35-6 would settle over a few days, while older machines in his yard held position for weeks. After consulting with Yanmar service reps, he confirmed that the behavior was within spec and advised his team to always park with the boom down.
Another technician shared that he replaced boom seals on a similar machine, only to find the settling persisted. The issue was traced to the control valve block, where minor internal leakage allowed pressure to equalize over time.
Conclusion
Boom settling on the Yanmar VIO35-6 is a result of hydraulic system design and is generally not a cause for concern. By understanding cylinder drift and following best practices for shutdown, operators can avoid unnecessary repairs and ensure safe machine storage. In compact excavators, gravity never sleeps—and the boom always finds its way down.
The Yanmar VIO35-6 mini excavator is known for its compact zero-tail design and efficient hydraulic system, but some owners report that the boom slowly settles after the machine is shut down. This behavior is not necessarily a defect—it falls within the acceptable range of hydraulic cylinder drift defined by manufacturers. For the VIO35-6, settling of the boom over several hours or days is considered normal if it does not exceed specific tolerances.
Yanmar VIO35-6 Overview and Hydraulic Design
Yanmar introduced the VIO35-6 as part of its sixth-generation compact excavator lineup, targeting urban construction, landscaping, and utility work. With an operating weight of approximately 8,000 lbs and a 24.4 hp Tier IV Final diesel engine, the machine features a load-sensing hydraulic system and a variable displacement pump. The boom and arm cylinders are equipped with standard piston seals and check valves, but not all models include load-holding valves or pilot-operated check valves on the boom circuit.
Terminology Notes
- Cylinder Drift: The gradual movement of a hydraulic actuator due to internal leakage or pressure equalization.
- Load-Holding Valve: A valve that prevents unintended movement of a hydraulic cylinder under load.
- Pilot-Operated Check Valve: A valve that locks hydraulic pressure until a pilot signal allows flow.
- Boom Settling: The downward movement of the boom when the machine is off and hydraulic pressure is no longer maintained.
When the engine is turned off, hydraulic pressure bleeds off through the control valve stack. If the boom is left raised, gravity acts on the cylinder, and any internal leakage past the piston seals or through the valve block allows the boom to slowly lower. This is especially noticeable in newer machines with tight tolerances, as the movement may be slow but still present.
Manufacturers typically allow up to 10 mm of cylinder movement per hour at operating temperature. Over several days, this can result in visible boom settling. Machines like older Kobelco or Kubota models may appear to hold position longer due to different valve configurations or tighter seal designs.
Preventive Practices and Operator Advice
- Always lower the boom to the ground when parking the machine. This eliminates the risk of settling and improves safety.
- Do not rely on hydraulic pressure to hold attachments in place during storage.
- Inspect cylinder seals and valve blocks if the boom drops rapidly or within minutes—this may indicate excessive internal leakage.
- Consider installing pilot-operated check valves on the boom circuit if long-term holding is critical, such as in lifting applications.
A rental fleet manager in Illinois noted that his VIO35-6 would settle over a few days, while older machines in his yard held position for weeks. After consulting with Yanmar service reps, he confirmed that the behavior was within spec and advised his team to always park with the boom down.
Another technician shared that he replaced boom seals on a similar machine, only to find the settling persisted. The issue was traced to the control valve block, where minor internal leakage allowed pressure to equalize over time.
Conclusion
Boom settling on the Yanmar VIO35-6 is a result of hydraulic system design and is generally not a cause for concern. By understanding cylinder drift and following best practices for shutdown, operators can avoid unnecessary repairs and ensure safe machine storage. In compact excavators, gravity never sleeps—and the boom always finds its way down.
