Desanders for trenchless horizontal directional drilling (HDD) separate solids, such as sand and other abrasive particles, from the drilling fluid, or "mud". This process allows for the recycling of drilling mud, which reduces costs and minimizes environmental impact. 

How desanders for HDD work
A typical HDD mud recycling process involves a series of steps to clean the slurry, and a desander is a critical part of this multi-stage separation. 

1. Initial screening: Used drilling fluid from the borehole is first sent to a shale shaker. This device uses high G-force vibrations and layered screens to remove the largest solids, like rocks and large cuttings.
2. Desanding: A centrifugal pump transfers the screened fluid to the desander's hydrocyclone cone(s). The slurry is pumped into the wide upper section of the cone at a tangent, creating a strong circular motion.
3. Cyclonic separation: The centrifugal force throws heavier solid particles against the walls of the cone. These solids spiral downward and exit from the bottom.
4. Recycling: The cleaner, lighter fluid travels up through the center of the cone and exits through an outlet at the top. This clean fluid is then ready for reuse.
5. Desilting (optional): For finer solids separation, the fluid from the desander can be sent through a desilter, which uses smaller hydrocyclone cones to remove even smaller particles. 

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