A raise boring machine depends on a powerful hydraulic motor to drive its drill head. This hydraulic motor is the heart of the machine. It must deliver smooth, high-torque output under heavy loads. At deep underground drilling sites, the raise borer is a pioneering machine.
At deep-hole drilling sites hundreds of meters underground, the raise borer is a pioneering beast. At its core sits a single hydraulic motor built for punishing conditions.
When faced with high-hardness rock formations, the drill rig itself needs a strong, robust structure. Its power core—the hydraulic motor—must also deliver powerful, steady output during high-load, low-speed operation.
However, in actual construction, a problematic situation often arises unexpectedly. When the drill rig bores through hard rock at low speed under heavy loads, the power head can jerk intermittently. This is the so-called “crawling” phenomenon. At the same time, the hydraulic pump station’s piping vibrates violently, and a piercing high-frequency noise fills the machine room.
In hydraulic engineering, this is known as system fluid oscillation, or the water hammer effect. It is caused by a flow interruption in the distribution valve. It is more than a sign of inefficiency. It is also a “silent killer” that can cause serious damage. It can shatter high-value drill pipes, dislodge alloy teeth from the cutterhead, and trigger borehole collapse or bit jamming.
So how can a raise boring rig deliver smooth, unimpeded power under such extreme conditions?
To answer that, we’ll start with the fundamentals of hydraulic science. From there, we’ll introduce the benchmark for power in heavy-duty mining excavation: the MS Series internal-curve radial piston hydraulic motor. We’ll also show how its quality empowers our AT3000-L raise boring rig.
As is well known, a raise boring rig first drills a guide hole several hundred millimeters in diameter. This hole runs from top to bottom, or bottom to top, penetrating the upper and lower sections. Next, a reaming cutterhead—often two or three meters in diameter—is installed. It “gnaws” through the guide hole in reverse until it becomes a large shaft of the designed diameter.
The problem lies in the reaming step. The larger the cutterhead, the slower the rotational speed must be. Yet the torque needed to break through rock can be dozens of times higher than for a conventional drill rig. This places extremely demanding requirements on the drive system:
And at the heart of it all is often an unassuming yet crucial component: the hydraulic motor.
Compared to electric motors, hydraulic motors offer higher power density and a more compact design. This lets them deliver extremely high torque in limited spaces. They also feature strong overload capacity and support stepless speed control. This makes them well-suited to frequent forward-and-reverse operation and heavy-load impacts. That’s why hydraulic motors are indispensable in the core drive systems of machines from tunnel borers to raise boring rigs.
Among the many types of hydraulic motors, the multi-stroke radial piston motor is the “specialist” for low-speed, high-torque applications. It is inherently designed for slow speed and high torque.
The rotor’s core function is to convert pressure into force. It takes the pressure energy of the high-pressure hydraulic oil delivered by the pump. That energy passes through the piston as applied force. Ultimately, it becomes mechanical energy—torque and rotational speed—that drives the power head on the raise boring rig.
The piston and roller are typically installed as a single assembly within the rotor bore. The piston body is a cylindrical chamber that contains hydraulic fluid. Its function is to convert the pressure of high-pressure hydraulic fluid into a massive linear thrust that pushes outward. The roller sits in a V-shaped or spherical roller seat at the head of the piston body. It converts the piston’s outward thrust into a lateral, tangential force. This force drives the rotor’s rotation as the roller rolls along the wave-shaped surface of the stator. At the same time, it turns sliding friction into rolling friction, which keeps the motor from seizing under immense force.
The stator is the motor’s outer casing. Its inner wall has multiple peaks and troughs that form a precision wave-shaped cam track. During operation, the stator stays stationary and provides a reaction force. When the piston pushes the roller outward and reaches the downward slope, the stator’s incline takes over. It converts that linear thrust into a tangential rotational force. This makes the stator the core mechanical fulcrum for achieving high torque at low speeds.
The oil distribution system is a precision component. It diverts and distributes oil to the individual piston chambers. Its precision shows in how it controls the inflow and retraction of both high- and low-pressure oil. The distribution body must fit tightly against the rotating cylinder block. Otherwise, high-pressure oil leaks could cause the power head to lose force or malfunction. The oil can also reach pressures of several hundred kilograms, which risks forcing the end face open. To prevent this, the back of the distribution body features a hydraulic automatic compensation chamber. It ingeniously uses the force of the high-pressure oil itself to achieve dynamic clamping and oil sealing.
Bearings are mounted at both ends of the rotor. They stabilize the rotor and keep it rotating without eccentricity. They also withstand the enormous thrust and lateral impacts transmitted by the drill rig. The seals serve a dual purpose: sealing internally and protecting externally. Internally, they prevent hydraulic oil from leaking through gaps in the contact surfaces. Externally, they block mine dust to prevent internal contamination. Together, they ensure the motor’s long-term, stable operation under high pressure and heavy loads.
Even though they’re both called “internal curve radial piston motors,” their performance can vary dramatically, depending primarily on:
Volumetric efficiency measures a hydraulic motor’s ability to convert input flow into effective output speed. It reflects the motor’s overall sealing performance. The core focus is evaluating leakage losses of the working fluid during pressure transmission. A value between 90% and 98% is considered good. A higher volumetric efficiency means the distribution body fits more precisely against the cylinder block. That means a lower leakage rate.
Mechanical efficiency measures a hydraulic motor’s ability to convert input pressure energy into effective output torque. It reflects the degree of energy lost to friction within the motor during operation. The key is assessing how much driving force is lost to mechanical resistance during transmission. This frictional resistance directly consumes part of the torque, reducing effective output. For efficient operation, this value must stay at 90% or above.
In general, hydraulic motors operating below 10–50 RPM see severe torque fluctuations from sudden changes in internal friction. Industry-leading models can reach a minimum stable speed as low as 0.5 RPM, or even 0.1 RPM. High-quality radial piston motors with an internal curved bore can effectively prevent crawling and stick-slip.
Beyond the mandatory specifications, a raise boring rig’s hydraulic motors can also be optimized. Options include displacement choices, overload protection, pressure-relief buffering, and hydrostatic lubrication.
All right, so the next time you need to choose a hydraulic motor, you won’t feel lost.
The MS Series is a direct-drive, versatile hydraulic motor. It delivers a maximum output power of 140 kW and is designed specifically for wheeled machinery and tool drive systems. The motor has a displacement range of 3,500 to 6,011 cc/rev. Its maximum operating pressure is 450 bar, with a peak torque of up to 43,000 N·m. With its multi-speed design, it reaches a maximum speed of 225 rpm. This meets the dual demands of low-speed, heavy-load operation and high-speed travel.
| Parameter | Value | |
 | Maximum Displacement | 6011cc/rev |
| Maximum Power | 140KW/188HP | |
| Maximum Torque | 43000Nm/31715lb-ft | |
| Maximum Operating Pressure | 450.00Bar/6527.00PSI | |
| Maximum Speed | 225RPM | |
| Motor Type | Wheel Motor / Shaft Motor | |
| Brake System | Service Brake + Parking Brake |
Multi-speed Design: The MS Series uses a multi-speed concept, letting displacement switch according to operating conditions. This flexibility lets a single motor adapt to a wide range of conditions. It can shift from low speed and high torque to high speed and low torque.
Modular Design：
The modular design allows the MS Series hydraulic motor to be disassembled with ease. Each module performs a specific function and connects seamlessly with the others. This modular design adapts to a wide range of operating conditions and facilitates maintenance. It can also be flexibly configured to meet different application requirements.
Twin-Lock™ Technology：
Twin-Lock™ is a smart hydraulic anti-slip system that balances powerful traction with flexible steering. When a wheel slips, it instantly limits flow and redirects power to wheels with grip, enabling recovery. It ensures solid straight-line traction, then releases during turns—maximizing efficiency without vehicle deviation.
The AT3000-L (CY-R120V) is a fully hydraulic, intelligent, crawler-type raise boring machine. It is equipped with two MS Series.2.A16.A50 heavy-duty hydraulic motors, capable of delivering high torque at low speeds. During the initial design phase of this drilling rig, we faced tough technical challenges. These included high rotational torque, high rotational speed, and limited installation space. The traditional “high-speed motor + gearbox” solution failed to meet our reliability and size requirements. The gearbox also needed regular inspection and oil changes. Ultimately, we adopted the MS Series of low-speed, high-torque motors and put them into mass production on the AT3000-L.
In deep-hole drilling operations in underground mines, raise boring rigs must perform large-diameter, high-precision, long-distance drilling within confined spaces. The AT3000-L (domestic model CY-R120V) is China’s first self-propelled, intelligent, large-diameter raise boring rig. It has a nominal reaming diameter of 3,000 mm. Its maximum drilling depth is 400 m, or up to 500 m when f ≤ 14. Its required well deviation rate is controlled within 0.5%. To manufacture the AT3000-L to these demanding specifications, we chose a hydraulic motor with high compatibility and robust power. We found that the MS Series heavy-duty piston motor perfectly meets the AT3000-L’s required specifications and operational standards. It gives the rig superior drilling efficiency and an excellent construction experience.
The limited space in underground mine chambers imposes strict requirements on equipment dimensions. The MS Series features a modular design. Each motor weighs approximately 400 kilograms and has a displacement of up to 6,011 cc. That’s a significant size advantage over large, heavy hydraulic motors. The two MS Series motors are also arranged in an axially symmetrical configuration. This enables direct drive of the power head spindle and greatly enhances construction stability.
The MS Series hydraulic motor features a dual-displacement function. This lets it flexibly switch between displacement modes to meet the needs of different operating phases. During the pilot hole stage, the motor runs in low-displacement mode. It uses high speed and low torque to drive the drill bit downward, quickly and efficiently forming the pilot hole. When the reaming stage begins, the motor seamlessly switches to high-displacement mode. It shifts to low speed and high torque, giving the drill bit continuous, smooth, jam-free pull-up force and cutting torque. This dual-displacement design lets a single motor meet two very different operating conditions: pilot hole drilling and reaming. There’s no need to replace the motor or reconfigure the gearbox.
During reaming operations, the AT3000L must break through hard rock formations. This calls for a rated torque of 168 kN·m and a peak torque of 192 kN·m. The Poclain MS Series motors have a maximum displacement of 6,011 cc/rev. They can deliver a maximum torque of 43,000 N·m at an operating pressure of 450 bar. Maximum power output reaches 140 kW. Working in tandem, the two MS Series motors give the drill rig ample torque reserve and power redundancy. This ensures continuous, stable power output when drilling through hard rock. At the same time, the two motors’ combined power is matched to the rig’s 160 kW main motor. This enables efficient use of the power source.
The AT3000-L (CY-R120V) raise boring rig and the MS Series hydraulic motor together form a proven, high-performance solution. It’s built for the most demanding underground drilling conditions. The MS Series’s dual-displacement capability, low-speed stability, and high torque match the AT3000-L’s needs for pilot hole drilling and reaming. Together, they deliver smooth, jam-free operation and exceptional borehole accuracy.
We are proud to offer both the MS Series hydraulic motor and the AT3000-L raise boring rig. You can choose them as individual components or as a fully integrated system. Whether you need to upgrade an existing rig or build a new fleet, our team can help. We provide the right configuration, technical support, and after-sales service to keep your projects on track.
Want to learn how the MS Series and AT3000-L can boost efficiency, cut downtime, and lower total cost of ownership? Contact us today. Let us help you power through hard rock with confidence.
