Centralized lubrication systems are widely used across various machine tools, enabling automatic, precise, and metered oil delivery to moving components such as guideways. The primary types employed in machine tools are resistance-type and volumetric-type systems. What distinguishes these two types?

1. Working Principle

Resistance-type (also known as resistance-based): Resistance-type lubricating oil pumps primarily operate by utilizing changes in fluid resistance during flow through pipelines. For example, some simple drip lubrication devices control oil droplet rate through the oil's own gravity and resistance generated by small orifices or fine tubes. This method delivers relatively unstable oil supply, easily affected by factors such as oil viscosity, temperature, and pipeline conditions. When oil viscosity increases (e.g., at lower temperatures), flow resistance rises, slowing the dripping rate; conversely, reduced viscosity may accelerate dripping.

Volumetric-type: Positive displacement lubricating oil pumps deliver lubricant through periodic changes in the volume of sealed working chambers. For example, a gear oil pump primarily consists of two meshing gears. As the gears rotate, the side where the gears disengage increases in volume, creating a low-pressure zone that draws in lubricating oil. Conversely, the side where the gears engage decreases in volume, forming a high-pressure zone that expels the lubricating oil. This operating principle directly links the pump's output volume to its rotational speed and the volumetric change within the working chamber. As long as the rotational speed remains stable and the chamber maintains good sealing integrity, a relatively consistent oil supply can be ensured.

2. Oil Supply Characteristics

Resistance-type: The control precision of oil supply is relatively low, with output flow typically ranging within a certain range rather than maintaining a fixed value with high accuracy. Furthermore, during actual operation, external factors may cause significant fluctuations in oil supply volume. For instance, in simple oil-drip lubrication systems, the dripping rate may initially be faster when the oil reservoir is full compared to when it nears emptiness. This occurs because changes in reservoir liquid level cause pressure variations that affect the dripping speed.

Volumetric-type: Provides relatively precise and stable oil supply. By rationally designing the pump's displacement (the change in working chamber volume) and controlling the rotational speed, the oil supply per unit time can be precisely regulated. For instance, in the lubrication systems of precision machine tools, where the lubricant volume at each lubrication point must be precisely controlled, positive displacement oil pumps effectively meet this requirement. They ensure all machine components receive adequate lubrication, thereby extending equipment service life.

3. Applicable Scenarios

Resistance-type: Suitable for simple mechanical devices with low lubrication requirements, light loads, and low rotational speeds. Examples include small hand tools and household appliances. In such equipment, fluctuations in lubricant supply do not significantly impact normal operation. For instance, older household sewing machines can meet their basic lubrication needs through simple oil hole drip lubrication.

Volumetric-type: Widely used in industrial equipment, automobiles, construction machinery, and other applications with high lubrication demands. These devices typically require stable, long-term operation under high-load, high-speed conditions. For instance, automotive engine lubrication systems employ positive displacement oil pumps to ensure a steady, reliable oil supply to moving components across all engine conditions (idling, high-speed driving, etc.), preventing wear and overheating.

4. Structural Complexity

Resistance-type: Features relatively simple construction, typically comprising a basic oil reservoir, oil lines, and flow-restricting components (such as orifices or narrow tubes). This straightforward design results in lower costs and ease of maintenance. For instance, simple manual lubricating oil pots require only periodic oil replenishment and inspection of oil lines for blockages.

Volumetric-type : Features a relatively complex structure incorporating multiple moving components (e.g., gears in gear pumps, rotors in rotary pumps) and seals. These components require precision machining and meticulous assembly to ensure the sealing integrity of the working chambers and the accuracy of volumetric changes. For instance, screw-type positive displacement pumps demand high machining precision for their screws and depend on reliable sealing structures, resulting in higher manufacturing costs. Additionally, their maintenance requires specialized knowledge and skills.