A11VO for roadheader

The A11VO for roadheaders is a high-pressure axial piston variable displacement pump developed by Rexroth for open hydraulic systems in coal mine and tunnel cantilever roadheaders. As the power heart of the roadheader's hydraulic system, it supplies pressurised oil to circuits such as the cutting arm, track travel, star wheel loading, scraper conveyor and spray cooling.

The underground operating conditions for roadheaders are extremely harsh: severe impact loads during cutting, continuous and intense vibration of the entire machine, high dust levels, confined tunnel spaces, and low temperatures and high humidity underground. As the pump housing is often installed above the oil tank, the A11VLO version with a built-in impeller make-up pump is the preferred choice for medium to large models to minimise cavitation damage.

First, mainstream control modes for roadheaders

The vast majority of underground roadheaders utilise an LRDS (Constant Power + Pressure Cut-off + LS Load Sensing) composite regulator, which is standard equipment on the EBZ series of roadheaders.

1. LR Constant Power Control: When cutting loads on hard rock increase, the pump automatically reduces its displacement to limit the absorbed torque, thereby preventing the explosion-proof motor from overloading and stalling. The power setting can be adjusted externally whilst the machine is in operation to match the motor's power output.

2. LS Load-Sensitive Control: Enables coordinated operation of multiple actuators; during simultaneous cutting, travel and loading operations, flow is delivered on demand, reducing heat generated by overflow and lowering the system's temperature rise.

3. DR Pressure Cut-Off: In the event of the cutting head jamming or instantaneous overpressure caused by encountering hard rock, the pump rapidly reduces displacement to protect cylinders, motors and piping, thereby avoiding the risk of underground pipe bursts.

Second, Key Advantages of the A11VO for Tunnel Boring Machines

1. Highly Impact- and Vibration-Resistant Structure

Cutting through rock generates erratic and violent impact vibrations. The swashplate damping structure absorbs impact forces fed back from the hydraulic system, whilst the plunger-slide shoe and distribution plate utilise wear-resistant alloy processes to withstand continuous, intense underground vibration conditions, thereby reducing the likelihood of damage to bearings and distribution plates.

2. Through-shaft Series Configuration Suitable for Compact Machine Frames

Underground roadheaders have compact machine frames; 100% through-shaft drive enables the series connection of dual main pumps, with a gear pump connected at the end, simultaneously supplying oil to the main circuit and the spray cooling circuit. This reduces the number of transmission components, simplifies the overall machine layout and minimises potential failure points.

3. A11VLO addresses the issue of cavitation underground

Hydraulic pumps on roadheaders are often mounted above the oil tank. In the low-temperature environment of mine tunnels, where oil viscosity is high, standard VO pumps are prone to cavitation, resulting in abnormal noises and pitting on the distribution plate; the VLO's built-in impeller actively pressurises the oil supply, significantly extending the overhaul intervals underground.

4. LRDS Composite Control Adapted for Underground Explosion-Proof Motors

Constant power strictly limits the absorbed torque, preventing overload and stalling of explosion-proof motors; the pressure cut-off function prevents damage to hydraulic components caused by locked-rotor impacts, thereby enhancing the safety of underground equipment. Load-sensing technology enables simultaneous operation of multiple mechanisms - such as cutting, travel and loading - ensuring smooth operation.

5. Modular Valve Blocks for Convenient Underground Maintenance and Commissioning

The regulator valve block can be removed and installed separately without dismantling the pump core; constant power and cut-off pressure parameters can be adjusted on-site underground; SAE standard interfaces ensure good interchangeability of mining spare parts.

Third, Key Points for Underground Operation and Maintenance

1. Keep the suction line as short as possible, minimise the number of bends, ensure sufficient bore diameter, and reduce suction resistance; for large-displacement roadheaders with a displacement of 130 cc or above, the VLO oil-supplement version must be selected.

2. The housing drain pipe must return oil to a separate sump; it must not be combined with the main return line, as excessive back pressure may cause the pump to overheat, leading to seal failure and oil leakage.

3. Due to high levels of coal dust underground, strictly adhere to the replacement intervals for hydraulic fluid and filter elements; hydraulic fluid contamination is the primary cause of internal scuffing and increased internal leakage in the pump.

4. Commissioning points: The pressure cut-off is generally set at 370-390 bar; constant power parameters must be matched to the rated power of the explosion-proof motor to prevent motor overload or loss of power in the entire unit.

5. For dual-pump series systems, ensure coaxiality to prevent damage to the drive shaft caused by additional radial forces.