Sizing a cyclone bank is where a lot of rigs quietly lose ground — not because the math is hard, but because the wrong number goes into it. The rule is not ‘match the circulation rate.’ It is that the cones must process at least 100% of all the fluid entering the hydrocyclone’s suction compartment, and preferably more. Get that input right and the cone count falls out cleanly.
The 100% rule — and what ‘100%’ is measured against
Hydrocyclones have no way to process fluid selectively; they take suction from a tank compartment and must clear everything arriving there, independent of the rig’s circulation rate. So the design target is that the number of cones in use processes at least 100% — preferably greater than 100% — of the flow rate of all fluids entering the suction compartment. That total is usually more than the circulation rate, because mud guns, transfer flow and returns all feed the same compartment.
Use a complete compartment volume balance to establish treatment flow and any required backflow. A fixed 100-gpm backflow is not a universal requirement and does not guarantee complete processing. Check tank levels, routing, pump capacity and actual solids removal. Related reference
Cone capacities you size against
Cone ratings depend on the model, geometry, specified head and fluid properties. Use OEM flow and separation data at actual duty. Example values such as 500 gpm per 10-inch cone or 60 gpm per 4-inch cone are sizing assumptions, not universal performance guarantees.
Per-cone ratings apply to the stated OEM head, fluid and cone configuration. Use the actual operating duty and measured flow when checking bank capacity; there is no universal 75-ft pass/fail threshold. Related reference
Working the count
Calculate the required cone count from the treatment-flow target and OEM per-cone flow at the selected duty. Round up, then check pump, piping, solids loading and the complete tank balance. Select spare capacity and backflow from the actual design rather than fixed generic margins.
Illustrative arithmetic: at an assumed 60 gpm per cone, 800 gpm requires at least 14 cones for nominal hydraulic throughput (840 gpm); 16 gives 960 gpm. At an assumed 500 gpm per cone, two provide 1,000 gpm. These counts do not guarantee complete solids removal or an acceptable tank balance; verify OEM ratings, pump capacity and routing. Related reference
The sizing method
Cones = flow into the suction compartment ÷ per-cone capacity — round up so installed capacity ≥ 100% (aim >100%).
Per cone @ 75 ft head: 10″ desander ≈ 500 gpm · 4″ desilter ≈ 40–100 (typ. 60) · micro-fine ≈ 15 gpm
Backflow: determine the required flow from the actual compartment balance and operating arrangement; a fixed 100 gpm is not universal.
Measure against all flow into the suction compartment — not the circulation rate.
Select per-cone flow from the OEM performance data at actual duty and use the full compartment balance. Round up the required cone count, check pump and manifold capacity, then verify solids removal; no fixed backflow guarantees performance.
Common questions
How many desilter cones do I need?
Divide the flow entering the desilter's suction compartment by the per-cone capacity (about 60 gpm for a 4-inch cone at 75 ft head) and round up so the installed capacity exceeds 100% of that flow. For 800 gpm that is 800 ÷ 60 ≈ 14 cones minimum, with 16 giving a comfortable margin.
Size treatment flow using the complete suction-compartment balance, including transfers and return streams. Set any backflow requirement from tank levels, routing and the actual design; 100 gpm is not a universal minimum.
Use OEM flow ratings at the specified head and fluid conditions for each cone model. A 10-inch cone at 500 gpm or a 4-inch cone at 60 gpm is an illustrative sizing input, not a universal rating; verify flow and separation in service.
