Of the three centrifuge levers, feed rate is the one most often used and least often understood. It feels like a throughput control — turn it up to process more mud — and it is. But it is also a separation control, because the rate you feed sets how long each particle stays in the pond, and residence time is what decides the finest solid the machine can actually catch. Run the feed too high to “keep up,” and you quietly hand back the fine-solids removal you bought the centrifuge for.
Feed rate is really a residence-time control
A particle is only removed if it has time to settle from the centre of the pond out to the bowl wall before the liquid carries it over the weir. That available time is the residence time, and it falls as feed rate rises — more slurry pushed through the same pond volume means each drop spends less time inside.
- Lower feed rate — longer residence, so smaller particles have time to reach the wall. The machine reaches a finer cut, and because solids are less crowded, the cake also tends to come out drier. The cost is throughput: you process less mud per hour.
- Higher feed rate — shorter residence, so only coarser particles settle in time. The cut goes coarse, fine solids escape over the weir back into the system, and the solids load on the scroll climbs toward overload.
Where the cut is set — and where overload begins
Every decanter has a feed rate at which it makes the cut it was set up for, and a higher rate at which it stops. Between them, performance degrades smoothly: the cut creeps coarser, the liquid carries more fines, the cake gets wetter. Beyond it, the failure is abrupt — the bowl takes in more solids than the scroll can convey, accumulates, and heads for a packed bowl and a torque trip.
| Feed rate | Residence time | Cut point | Result |
|---|---|---|---|
| Low | Long | Finest | Best fines removal, drier cake, low throughput |
| Matched to duty | Adequate | On target | Design separation at rated capacity |
| Too high | Short | Coarse | Fines escape, wet cake, build-up, overload |
Reading it on the rig
Two signs tell you the feed is too high without any lab work: the liquid discharge looks dirty (fines going over the weir that should be in the cake), and scroll torque climbs as solids load builds. Two signs tell you it is too low: very clean liquid but low solids discharge, and a machine that is clearly under-fed for the load it could handle. The right feed sits between — clear liquid, steady torque, a continuous solids discharge — and it shifts as mud weight and solids load change through the well.
Key takeaways
Feed rate controls separation as much as throughput, because it sets residence time and residence time sets the cut. Feed low for the finest cut and driest cake at lower volume; feed high to move more mud at a coarser cut, until residence collapses and the bowl overloads. The target is the feed that holds the cut you need — read off dirty-versus-clean liquid and steady scroll torque — not the highest number the pump can deliver. Rated capacities and target rates are machine- and mud-specific; the relationship between feed, residence and cut is universal.