1. Project Overview
This technical proposal is designed for a Hitachi Zaxis 200-5G 20-ton-class excavator equipped with a dual-pump hydraulic system.
The proposed system consists of:
One 8-inch hydraulic dredge pump
One 750 mm diameter hydraulic bottom auger / cutter head
Hydraulic motors and reduction gearbox
Hydraulic control valve system
Hydraulic hoses and protective guards
The complete system is designed to be directly powered by the excavator’s hydraulic system, without using an additional power pack.
The system is suitable for underwater sand, mud, gravel and sediment dredging applications in rivers, lakes, reservoirs, mining areas and other water environments.
2. Excavator Hydraulic System
The customer’s excavator is a:
Hitachi Zaxis 200-5G, approximately 20-ton class
According to the hydraulic specifications provided by the customer, the excavator is equipped with a dual-pump hydraulic system.
The main hydraulic pump capacity is approximately:
2 × 212 L/min
For the proposed system, the two hydraulic circuits can be used independently:
Circuit A → Main hydraulic dredge pump
Circuit B → 750 mm bottom auger
This independent hydraulic circuit arrangement allows the dredge pump and bottom auger to operate separately without competing for hydraulic oil flow.
TAIAN OCEAN PUMP CO.,LTD
DORIS CHEN
WHATSAPP :+86 18 562293319
EMAIL : oceanpump12@tsbeng.com
3. 8-Inch Hydraulic Dredge Pump
The main dredge pump is an 8-inch hydraulic dredge pump, designed for pumping and transporting sand, mud, slurry and solid particles.
Main Specifications
| Item | Specification |
| Pump outlet | 8 inch |
| Fresh-water capacity | Approx. 350 m³/h |
| Head | Approx. 30 m |
| Required power | Approx. 65 kW |
| Hydraulic motor | 107 cc/rev piston motor |
| Hydraulic oil flow | Approx. 160 L/min |
| Pump speed | Approx. 1,450 rpm |
The dredge pump is driven by a 107 cc/rev hydraulic piston motor.
According to the hydraulic data provided by the customer, Circuit A can provide approximately 212 L/min. Therefore, it has sufficient hydraulic flow to supply the approximately 160 L/min required by the dredge pump.
The actual working flow will be regulated by the hydraulic control valve according to the pump operating requirements.
4. 750 mm Bottom Auger / Cutter Head
A 750 mm diameter bottom auger is installed below the dredge pump.
The main functions of the auger are:
Loosening underwater sediment and sand;
Cutting and agitating compacted material;
Directing material toward the pump suction inlet;
Improving the pump’s material intake efficiency;
Helping the pump handle compacted sand, mud and gravel.
Main Specifications
| Item | Specification |
| Auger diameter | 750 mm |
| Main material | Manganese cast steel |
| Hydraulic motor | Internal multi-star hydraulic motor |
| Motor displacement | 2,000 cc/rev |
| Auger speed | Approx. 30–35 rpm |
| Hydraulic oil flow | Approx. 60 L/min |
| Reduction gearbox | Included |
| Hydraulic power | Approx. 20 kW |
5. Why Do We Use a 2,000 cc/rev Hydraulic Motor?
There is an important point that should be clarified.
2,000 does NOT mean 2,000 L/min.
The value 2,000 cc/rev refers to the hydraulic motor displacement.
It means that theoretically, the motor requires approximately 2 liters of hydraulic oil for one revolution.
The theoretical flow calculation is:
Q = D × n ÷ 1,000
Where:
Q = Hydraulic flow, L/min
D = Motor displacement, cc/rev
n = Motor speed, rpm
For a 2,000 cc/rev motor operating at 30 rpm:
2,000 × 30 ÷ 1,000 = 60 L/min
Therefore:
2,000 cc/rev at 30 rpm requires approximately 60 L/min hydraulic oil flow.
This is why a 2,000 cc/rev hydraulic motor is proposed for the bottom auger.
6. Why Use a Large-Displacement Motor at Low Speed?
The 750 mm diameter auger works underwater and may encounter sand, gravel, compacted sediment and other obstacles.
For this application, high torque is more important than high rotational speed.
Therefore, we recommend using:
Large-displacement hydraulic motor + reduction gearbox + low-speed auger
instead of directly using a small-displacement high-speed motor.
The proposed configuration is:
2,000 cc/rev hydraulic motor + reduction gearbox
with a final auger speed of approximately:
30–35 rpm
This configuration provides high output torque at low rotational speed and is more suitable for underwater cutting, loosening and agitation of sand, mud and gravel.
7. Auger Material Selection
The customer asked whether Cr26 or Cr27 high-chrome alloy could be used for the auger.
Cr26 and Cr27 high-chrome alloys provide excellent wear resistance and are suitable for highly abrasive applications.
However, high-chrome alloy also has certain limitations:
High hardness;
Excellent wear resistance
Relatively low toughness compared with manganese steel;
More brittle;
Less suitable for welding and field repair;
Higher manufacturing cost.
The 750 mm bottom auger may encounter rocks, gravel and other obstacles during operation. Therefore, impact resistance and toughness are also very important.
For this reason, we do not recommend manufacturing the complete auger from Cr26/Cr27 high-chrome alloy.
Our recommended solution is:
Manganese cast steel for the main auger structure + replaceable wear-resistant components for high-wear areas.
This provides a better balance between:
Wear resistance
Toughness
Impact resistance
Weldability
Service life
Manufacturing cost
8. Independent Hydraulic Circuits
The most important feature of this system is that the excavator’s two hydraulic circuits are used independently.
Circuit A – Main Dredge Pump
The hydraulic arrangement is:
Circuit A → Pressure-compensated hydraulic control valve → 107 cc/rev hydraulic motor → 8-inch dredge pump
Required flow:
Approx. 160 L/min
Available theoretical flow:
Approx. 212 L/min
Therefore, Circuit A has sufficient flow capacity for the main dredge pump.
Circuit B – Bottom Auger
The hydraulic arrangement is:
Circuit B → Hydraulic control valve → 2,000 cc/rev hydraulic motor → Reduction gearbox → 750 mm bottom auger
Required flow:
Approx. 60 L/min
Available theoretical flow:
Approx. 212 L/min
Therefore, Circuit B also has sufficient flow capacity for the bottom auger.
The actual flow will be regulated to approximately 60 L/min by the hydraulic control system.
9. Hydraulic Power and Working Pressure
Hydraulic power is related to both flow and pressure.
The basic calculation is:
P = Q × ΔP ÷ 600
Where:
P = Hydraulic power, kW
Q = Hydraulic flow, L/min
ΔP = Differential pressure, bar
For example, if the bottom auger requires approximately 20 kW at a flow of 60 L/min:
20 × 600 ÷ 60 ≈ 200 bar
Therefore, the hydraulic system would theoretically require approximately 200 bar differential pressure under this operating condition.
However, the actual working pressure depends on:
Auger load;
Motor efficiency;
Reduction gearbox efficiency;
Hydraulic system efficiency;
Excavator relief-pressure setting;
Actual operating conditions.
The same principle applies to the 65 kW main dredge pump.
Therefore, flow alone is not sufficient to determine whether the excavator can provide the required hydraulic power.
10. Hydraulic Hose and Protection Design
Because the equipment will operate underwater and close to the riverbed, hydraulic hoses may be exposed to:
Rocks;
Gravel;
Riverbed obstacles;
Mud and sand;
Mechanical movement;
Contact with other equipment.
Therefore, the hydraulic hose arrangement should be designed to:
Minimize exposed hose length + keep the hoses close to the pump assembly + secure the hoses properly + provide protective guards.
For the standard configuration, the hydraulic hoses between the pump and auger assembly can be approximately:
2.5 m per set
If the customer requires approximately 25 m hydraulic hoses, the pressure loss and hydraulic system configuration should be recalculated because the longer hose length will increase pressure loss and may affect the motor flow and operating performance.
We can arrange the:
Hydraulic oil inlet line
Hydraulic return line;
Drain/case-drain line;
in a compact and protected configuration.
A hydraulic manifold/diverter valve and oil collection/manifold valve can also be used to organize the hydraulic hoses and keep the connections tidy.
Protective covers/guards will be installed around exposed hydraulic hoses to reduce the risk of impact and abrasion.
Whenever possible, the hydraulic hose connections will be positioned as close to the pump and auger assembly as practical.
This minimizes the amount of hose exposed near the riverbed and reduces the possibility of the hoses being hit by underwater obstacles.
11. Recommended Overall Configuration
Main Hydraulic Dredge Pump
8-inch Hydraulic Dredge Pump
Outlet: 8 inch
Capacity: Approx. 350 m³/h
Head: Approx. 30 m
Required power: Approx. 65 kW
Hydraulic motor displacement: 107 cc/rev
Hydraulic flow: Approx. 160 L/min
Pump speed: Approx. 1,450 rpm
Bottom Auger / Cutter Head
750 mm Hydraulic Bottom Auger
Diameter: 750 mm
Main material: Manganese cast steel
Hydraulic motor: Multi-star hydraulic motor
Motor displacement: 2,000 cc/rev
Reduction gearbox: Included
Auger speed: Approx. 30–35 rpm
Hydraulic flow: Approx. 60 L/min
Hydraulic power: Approx. 20 kW
Excavator
Hitachi Zaxis 200-5G
Approx. 20-ton class
Dual hydraulic pump
Main pump capacity: Approx. 2 × 212 L/min
Circuit A: Main dredge pump
Circuit B: Bottom auger
12. Technical Conclusion
Based on the hydraulic parameters currently provided by the customer, the proposed dual-circuit hydraulic system is technically feasible from the hydraulic flow capacity perspective.
The proposed arrangement is:
Circuit A: 212 L/min available → approximately 160 L/min required by the dredge pump
Circuit B: 212 L/min available → approximately 60 L/min required by the bottom auger
Therefore, both circuits have sufficient theoretical flow capacity.
The 2,000 cc/rev specification refers to the hydraulic motor displacement and does not mean 2,000 L/min hydraulic flow.
At 30 rpm:
2,000 cc/rev × 30 rpm ÷ 1,000 = 60 L/min
For the 750 mm bottom auger, the combination of a 2,000 cc/rev large-displacement hydraulic motor + reduction gearbox is suitable for achieving low rotational speed and high output torque.
For the final engineering confirmation, we recommend that the customer provide the actual hydraulic specifications of the Hitachi Zaxis 200-5G, including:
Maximum auxiliary hydraulic flow;
Continuous working pressure;
Maximum hydraulic pressure;
Return-line pressure;
Case-drain pressure;
Auxiliary hydraulic port specifications;
Hydraulic oil tank capacity;
Hydraulic oil cooling capacity.
After confirming these parameters, we can finalize the hydraulic motor model, hydraulic control valve, pressure setting, hose specifications and complete pump-and-auger configuration.
TAIAN OCEAN PUMP CO.,LTD
DORIS CHEN
WHATSAPP :+86 18 562293319
EMAIL : oceanpump12@tsbeng.com
