Basic structure and composition
Hydraulic rotary joints are usually composed of the following core components:
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Casing (stator)
fixed to the lower vehicle (chassis) of the excavator, connected to fixed pipelines such as hydraulic pumps and oil tanks.
Rotor (rotating body)
rotates synchronously with the upper vehicle (rotating platform), and connects the hydraulic pipelines of the actuator (such as boom cylinder, rotary motor, etc.).
Sealing system
multi-layer sealing rings (such as polyurethane or Teflon) isolate different oil channels and prevent leakage.
Oil channel design
annular oil grooves are opened on the casing and rotor, and independent oil channels are formed through axial or radial channels.
working principle
Final Solution
Hydraulic Oil Circuit Connection
Oil Circuit Distribution: The high-pressure oil output by the hydraulic pump enters the rotary joint through the housing, and is distributed to the various actuators on the vehicle (such as the boom, dipper rod, bucket cylinder or rotary motor) through the annular oil groove and the corresponding holes of the rotor.
Independent Channel: Each oil channel corresponds to an independent function (such as the A/B port to control the extension and contraction of the oil cylinder), which is isolated by the sealing ring to prevent oil cross-flow.
Rotary Seal and Leakage Prevention
Dynamic Seal: The rotor and the housing are sealed by multiple layers of sealing rings to keep the oil circuit closed even when rotating. The sealing ring needs to be resistant to high pressure (usually 20-35MPa), wear-resistant, and adaptable to frequent rotation.
Pressure Balance: Some designs use a balance groove or a pressure relief channel to reduce the pressure difference on both sides of the seal and extend the seal life.
Rotary Support
Bearing Function: The bearing (such as a needle bearing or a sliding bearing) supports the rotor to rotate smoothly, reduces friction resistance, and at the same time bears the axial and radial loads when the vehicle rotates.
Key features
Multi-channel design: Modern excavator slewing joints usually integrate 4 to 12 oil circuits to control different actuators.
High pressure tolerance: Adapts to high pressure fluctuations in hydraulic systems (peak value can reach 40MPa).
360° unlimited rotation: The annular oil groove design allows the upper vehicle to rotate infinitely without affecting the oil circuit connection.
Common types
Single circuit: only transmits a single oil circuit (rarely seen in excavators, mostly used for simple equipment).
Multi-circuit integration: commonly used in excavators, integrating multiple oil circuits and circuits (such as pilot control oil circuits, sensor signal lines).
Electro-hydraulic integration: transmits hydraulic oil and electrical signals (such as sensor data, control signals) at the same time.
Maintenance and troubleshooting
Seal failure: Wear of the seal ring can lead to leakage and needs to be replaced regularly.
Bearing wear: Spinning jams or abnormal noises, bearings need to be lubricated or replaced.
Oil channel blockage: Contaminants (such as metal debris) may block the oil channel, and the filter element needs to be replaced regularly.
Application scenarios
Application scenarios
Continuous operation of excavators: When the vehicle rotates, the movements of the boom, bucket, etc. are kept unrestricted.
Other construction machinery: Aerial work vehicles, cranes, rotary drilling rigs and other equipment that need to rotate 360° also rely on this component.
The hydraulic swivel joint maintains the continuity of the hydraulic system during dynamic rotation through the design of seals and oil channels, which is the core guarantee of excavator operations. Its reliability is directly related to the working efficiency and maintenance cost of the equipment, so it is necessary to regularly check the seal and bearing status to ensure long-term stable operation.
