Swing arm garbage trucks, also commonly known as skip loaders, are frequently used sanitation vehicles for collecting and transporting municipal solid waste, construction waste, livestock manure, and sludge. Many people easily confuse them with hooklift garbage trucks, but their loading structures are completely different. Swing arm garbage trucks rely on a pair of swing arms paired with a lifting chain to lift the hopper and rotate it onto the chassis. All lifting, swinging, and resetting movements are driven and controlled by a hydraulic system.
Many buyers only focus on lifting capacity and chassis brand, neglecting the design of the hydraulic circuit. A properly matched, stable, and reliable hydraulic system directly determines the smoothness of the swing arm movement, operational safety, and the overall service life of the vehicle. This article will introduce the hydraulic components, the complete working cycle, mainstream circuit types, built in safety protection, and common hydraulic faults.
I.What Are The Main Components Of A Hydraulic System?
The hydraulic assembly converts engine power into the slewing power of the double swing arms. The core components are as follows:
Power Take-Off (PTO): Mounted on the chassis gearbox. When engaged, it transmits engine power to drive the hydraulic pump, serving as the power source for the entire hydraulic circuit.
Hydraulic Pump: Most small and medium sized swing arm garbage trucks come standard with a gear pump; heavy duty models requiring long term, high frequency operation use a piston pump. Its function is to convert rotational mechanical energy into hydraulic pressure energy.
Hydraulic Oil Tank: Stores hydraulic oil, featuring a built in filter, level gauge, and temperature observation window for filtering impurities and dissipating heat.
Multi-way Directional Valve: The control center. The operator switches the oil flow direction via a manual lever or an optional wireless control device, driving the individual cylinders.
Dual Synchronous Main Cylinders: A pair of matching cylinders used to drive the left and right swing arms to lift and swing synchronously.
Outrigger Cylinders (Optional): Hydraulic support legs. Extend downwards before lifting the heavy duty hopper, stabilizing the chassis and preventing tipping.
Balance Valve and Hydraulic Lock: Core safety components that lock the cylinders to prevent sudden drops of the loaded hopper.
Relief valve, hydraulic lines, quick couplings, pressure gauges: The relief valve limits the maximum pressure of the system and provides overload protection.
II.How Does Swing Arm Garbage Truck Hydraulic System Work?
The entire operation consists of 5 standard steps, controlled by a multiway valve assembly:
Step 1: Extend the outriggers (optional for heavy load)
The operator switches the control valve, pressurized oil enters the outrigger cylinders, and the outriggers extend downwards to the ground, securing the vehicle chassis.
Step 2: Lowering the Swing Arms to the Ground
The main hydraulic cylinder of the swing arm retracts, and both swing arms swing backward, lowering to ground height. The operator manually attaches the lifting chain at the end of the swing arm to the bucket lifting lug.
Step 3: Lifting the Hopper and Rotating it onto the Vehicle
Hydraulic oil enters the rodless chamber of the dual main cylinders, causing both cylinders to extend synchronously and push the swing arm to rotate upwards. The hopper lifts off the ground, rotates over the vehicle frame, and lands smoothly on the vehicle body.
Step 4: Lifting and Unloading
Upon reaching the unloading point, the hydraulic system continues to drive the swing arm to rotate upwards, and the hopper tilts along with the swing arm, allowing the waste to slide out of the hopper's outlet. After unloading is complete, the swing arm reverses its direction, lowering the empty hopper back to the ground.
Step 5: Reset and Retract Outriggers
Disconnect the lifting chain and rotate the boom back to the horizontal standby position. If the outriggers were previously extended, retract them, disconnect the power take off, and the vehicle can be moved to another location.
III.Two Typical Hydraulic Circuit Designs
| Type | Features | Suitable Scenarios |
| Manual Multiway Valve Hydraulic System | Low cost, simple maintenance, stable structure, joystick control | Standard small and medium tonnage swing arm garbage trucks, mainstream models on the market. |
| Electro Proportional/Remote Controlled Hydraulic System | Wireless remote control operation, adjustable lifting speed, built in buffer to reduce impact between the swing arm and the hopper | Large scale, high frequency sanitation projects, high end customized versions |
IV.Built In Hydraulic Safety Mechanisms
These security features are key areas that buyers need to focus on:
- Overflow Overpressure Protection: When the hopper is overloaded, the overflow valve automatically releases pressure, protecting the cylinders, pipelines, and swing arm structure from damage.
- Balance Valve + Hydraulic Lock (Fall Protection): If a hydraulic pipeline ruptures unexpectedly, the hydraulic lock will immediately lock the cylinder, preventing the loaded hopper from falling rapidly.
- Dual Cylinder Synchronous Control: Ensures consistent operating speed of the left and right swing arms, preventing hopper tilting and chain slippage.
- Outrigger Interlock (Optional): Lifting cannot start if the outriggers are not fully extended, preventing accidental tipping.
- Oil Temperature Protection: Prolonged continuous operation will cause the hydraulic oil to heat up; excessively high oil temperature will reduce lifting force and accelerate seal aging.
V.Common Hydraulic Faults & Root Causes
| Faults | Reasons | How to Solve |
| Slow swing, weak lifting | Insufficient hydraulic pump flow | Check if the pump speed and flow rate meet the standards; repair or replace the pump if necessary |
| Oil filter clogging | Clean or replace the filter element and check the cleanliness of the oil | |
| Oil viscosity is too high in low temperature environment | Replace with hydraulic oil that is compatible with the local low temperature rating | |
| Hydraulic pump internal wear | Disassemble and inspect the pump body, assess the degree of wear, and replace damaged parts | |
| The swing arm shook violently during the lifting process | Air mixed into the fuel system | Check the oil inlet line seal and perform system venting |
| Insufficient hydraulic oil | Add hydraulic oil to the specified level and check for any oil leaks | |
| Hydraulic Oil Leakage | Sealing ring aging | Replace the corresponding seals |
| Loose pipe joint | Retighten the joint to the specified torque | |
| System pressure exceeds set value | Check the relief valve set pressure to avoid prolonged overpressure operation | |
| Unable to maintain pressure and bear weight after stopping | internal leakage of the swing arm cylinder | Repair the hydraulic cylinder and replace the piston seal |
| Hydraulic lock or balance valve failure | Inspect the pressure holding valve assembly; replace if damaged | |
| Unsynchronized arm swing | The leakage rates of the two hydraulic cylinders are inconsistent | Test both cylinders separately and repair the cylinder with the larger leak |
| Uneven flow distribution in valve assembly | Check the flow splitting performance of the multiway valve; calibrate or replace it if necessary |
VI.Frequently Asked Questions
Q1: What is the biggest difference in hydraulics between a swing arm garbage truck and a hook arm garbage truck?
A: Swing arm garbage trucks use a double arm + chain rotation lifting system, requiring manual chain attachment; hook arm garbage trucks rely on a single hook arm to pull the container along the chassis, eliminating the need for a chain.
Q2: Is it necessary to install hydraulic outriggers on small swing arm garbage trucks?
A: Outriggers are optional on light load models under 5 tons; for heavy load conditions with hoppers of 6 tons and above, outriggers are strongly recommended to prevent tipping.
Q3: Can I modify the hydraulic system to lift heavier hoppers?
A: This is not recommended. The maximum lifting capacity is limited by the swing arm steel structure, cylinder specifications, and chassis frame strength. Simply increasing the pump pressure may cause structural deformation or even breakage.
Q4: Which type of hydraulic oil should be used in low temperature areas?
A: Use low temperature antiwear hydraulic oil that matches the lowest ambient temperature in the area to avoid viscous oil and slow hydraulic response.
VII.Conclusion
The hydraulic system is the core power unit of a swing arm garbage truck, relying on hydraulic oil to transmit power and achieve the unique swinging motion of the double swing arms. When purchasing a swing arm garbage truck, it's not enough to just compare lifting capacity; you also need to confirm the pump type, valve brand, whether it's equipped with a balance valve and hydraulic lock, and the dual cylinder synchronous design. A reliable hydraulic system can reduce downtime for maintenance and significantly improve the operational safety of solid waste collection projects.
