When buying a used excavator, the hydraulic pump, motor, and multi-way valve determine whether the machine can still work and whether it is cost-effective to operate. Here is the conclusion upfront: when choosing hydraulic parts, first check whether the pump's displacement and pressure rating match the whole machine, then inspect the housing for cracks and repair marks, and finally check whether the regulator is original. For mainstream 20-ton used excavators in China, an original used main pump costs between 12,000 and 28,000 yuan, and refurbished pumps priced below 8,000 yuan generally do not last.
How Much Do Hydraulic Parts Really Matter in Used Equipment?
A 20-ton used excavator has a total used price of about 280,000 to 450,000 yuan, and the hydraulic system accounts for 30% to 40% of the machine's value. The main pump, distribution valve, swing motor, and travel motor together can easily exceed 150,000 yuan if all are replaced with new ones. Many owners only look at whether the engine emits black smoke and how worn the undercarriage is when buying a machine, ignoring the condition of the hydraulic components. As a result, within three months the pump control valve sticks and the movements are half a beat slow, and one repair costs several thousand yuan.
Peers in the used construction machinery export business share a consensus: customers in the Middle East and Africa have stricter operating requirements for hydraulic pumps than for engines. In those regions, the weather is hot and oil temperatures are high, so pump volumetric efficiency drops quickly. If the displacement does not match correctly when selecting a used pump, high-temperature alarms will appear after only a few days on the job site. In a batch of used bulldozers we handled for Nigeria, the travel motor was matched with the wrong model, and the customer spent nearly 20,000 yuan modifying the piping themselves.
Hydraulic Pump Selection: How to Match Displacement, Pressure, and Control Method
- Displacement matching: Common models such as Kawasaki K3V112, K5V140, and Rexroth A8VO107 differ by one displacement step, and both movement speed and fuel consumption differ. The main pump displacement for a 20-ton excavator is generally 112 to 140 ml/rev, while a 30-ton class requires 180 or more.
- Pressure rating: Normal working pressure is 32 to 35 MPa, and pilot pressure is 3.5 to 4 MPa. If a used pump's rated pressure is below 30 MPa, it is either an old model or has severe internal wear.
- Control method: Negative flow control, positive flow control, and load sensing must match the original machine's multi-way valve. Using a load-sensing pump with a negative flow valve will cause jerky movements.
- Inspection points: Check whether the housing has weld repairs, whether the regulator shows signs of disassembly or repair, and whether the main shaft spline wear exceeds 0.5 mm. Used parts with test reports cost 15% to 20% more than those without, but they save trouble.
Motors and Multi-Way Valves: Two Major Items Easily Overlooked
Faults in the swing motor and travel motor are often misdiagnosed as pump problems. Internal leakage in the swing motor shows up as slow swing in one direction and inability to brake when stopping; wear in the travel motor shows up as deviation and weak climbing. A used swing motor costs 4,500 to 9,000 yuan, and a travel motor costs 6,000 to 12,000 yuan, depending on brand and condition.
The biggest fear in multi-way valve selection is spool sticking and incorrect relief valve settings. Used multi-way valves range from 3,000 to 15,000 yuan. Imported valves (Kawasaki, KYB, Toshiba) cost twice as much as domestic valves, but their response speed and fine control are indeed better. When buying a used valve, be sure to test whether the spool slides smoothly, and if possible, put it on a test bench to measure internal leakage.
Common Faults and Maintenance Intervals
- High hydraulic oil temperature: First check for a blocked radiator and return filter, then measure the pump's volumetric efficiency. If oil temperature exceeds 80°C for a long time, seal aging doubles.
- Slow and weak movements: Insufficient pilot pressure, low main relief valve setting, and pump regulator failure each account for about 30%. Do not rush to replace the pump; measure pressure first.
- Abnormal noise: Pump cavitation, damaged coupling rubber blocks, and bearing wear. Cavitation is mostly caused by a clogged suction filter or insufficient oil level.
- Maintenance intervals: Replace hydraulic oil every 2,000 hours, the return filter every 500 hours, and the pilot filter every 1,000 hours. On dusty job sites, filter replacement intervals should be shortened by one third.
FAQ
How can you tell whether a used excavator hydraulic pump is still usable?
Install it on the machine and measure flow and pressure. If flow is below 85% of the rated value or pressure cannot reach 30 MPa, it basically needs an overhaul or replacement. After disassembly, check the wear on the valve plate and plungers. Those with test reports are more reliable.
What refurbishment traps should you watch for when buying used hydraulic parts?
Refurbished parts usually have repainted housings, blurred nameplates, and new screw marks on the regulator. If the price is clearly more than 30% below the market average, it is most likely an assembled part. Ask the seller to provide a disassembly video and test data.
How much price difference is there between Kawasaki and Rexroth hydraulic pumps?
For used dismantled pumps of the same tonnage, Kawasaki is generally 12,000 to 22,000 yuan, while Rexroth is 20% to 35% more expensive, about 18,000 to 30,000 yuan. Rexroth lasts a bit longer, but parts are expensive and repair cycles are long.
What should be noted when exporting hydraulic parts to Africa?
Confirm voltage and pilot pressure specifications. Voltage is unstable at some job sites in Africa, and solenoid valves burn out easily. Packaging must be moisture-proof and rust-proof, and accompanying test reports and certificates of origin can save a lot of trouble during customs clearance.
How often should the hydraulic system of a used excavator be maintained?
Replace hydraulic oil every 2,000 hours for earthmoving conditions and every 1,500 hours for mining conditions. Check oil level and quality before starting the machine every day. If the oil turns black or contains metal particles, replace it early instead of pushing to the interval.
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