Hydraulic wood chippers are equipped with powerful infeed rollers that pull material into the chipping mechanism. Unlike gravity-fed chippers, which rely solely on gravity and the angle of the chute, hydraulic chippers provide active control over the feed rate. This control, combined with an understanding of the wood type, is key to influencing the size of the chips produced.

 

How Roller Speed Influences Chip Size

The primary relationship between roller speed and chip size is inverse:

  • Slower Roller Speed = Smaller Chips: When the infeed rollers move more slowly, the material is fed into the chipping disc or drum at a reduced rate. This allows the blades to make more cuts per unit length of wood, resulting in shorter, finer chips. Imagine taking very small bites with each pass.
  • Faster Roller Speed = Larger Chips: Conversely, increasing the speed of the hydraulic rollers feeds the material into the chipper more quickly. This means the blades take fewer cuts per unit length of wood, yielding longer, coarser chips. This is like taking bigger bites.

 

The Influence of Wood Type on Chip Size

Beyond just roller speed, the characteristics of the wood itself play a crucial role in the final chip output:

  • Hardwoods vs. Softwoods:
    • Hardwoods (e.g., Oak, Maple, Ash): These are generally denser and more fibrous. They tend to produce more uniform and consistent chips. When chipped, they often result in cleaner-cut pieces.
    • Softwoods (e.g., Pine, Spruce, Fir): These woods are typically less dense and can be more stringy or resinous. They might produce a wider range of chip sizes, and sometimes longer, stringier pieces, especially if fed too quickly or if the blades aren't perfectly sharp.
  • Green Wood vs. Dry Wood:
    • Green Wood (Freshly Cut): Contains high moisture content. It's often easier for the chipper to pull through, and it tends to produce more consistent chips due to its pliability. However, very wet wood can sometimes cause clumping in the discharge chute.
    • Dry Wood (Seasoned): Can be harder and more brittle. When chipped, dry wood, particularly hardwoods, may shatter more readily, leading to a higher percentage of smaller fragments or dust mixed in with the desired chip size. It can also be harder on the chipper blades.
  • Knotty or Irregular Wood: Pieces with many knots or unusual shapes can affect consistency. The chipper might struggle to feed them uniformly, leading to variations in chip size as the material twists and turns.

 

Adjusting the Roller Speed

Most hydraulic chippers designed for adjustable chip size will have a control mechanism for the feed roller speed. This can vary by manufacturer and model but typically involves:

  • Variable Speed Control Valve: Many hydraulic chippers are equipped with a valve or lever that allows the operator to regulate the flow of hydraulic fluid to the feed rollers. By increasing or decreasing this flow, you can directly control the speed at which the rollers pull material into the chipper.
  • Electronic Control Systems (Wallenstein P3 Pulse Intelligence): More advanced hydraulic chippers may incorporate electronic control systems (sometimes called "No-Stress" or "Smart" systems). While their primary function is to prevent engine bog-down by automatically regulating feed speed based on engine RPM, some systems may also offer a manual override or a setting to influence the overall feed rate, thus impacting chip size.

 

Practical Considerations and Tips

  • Engine/Tractor RPM: Ensure your chipper's engine or the tractor's PTO is operating at the manufacturer-recommended RPM. This provides the optimal power for the chipping mechanism itself. The roller speed adjustment fine-tunes the feed rate, not the main chipping rotor speed.
  • Experimentation: The best way to achieve your desired chip size is through experimentation. Start with a moderate feed rate and observe the chip output, then adjust the roller speed incrementally until you get the chip size you need, keeping the wood type in mind. You might need to slow the feed slightly more for very dry or knotty material to achieve a finer chip.
  • Blade Sharpness: Sharp blades are crucial for consistent chip size. Dull blades will tend to shred or tear the wood, producing more inconsistent chips and sawdust, regardless of roller speed.

By understanding and utilizing the hydraulic feed roller speed adjustment in conjunction with an awareness of the wood's characteristics, you can effectively control the output of your chipper, making it a versatile tool for various mulching, landscaping, and biomass needs.