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.
The companion rule is backflow. You want a backflow between the hydrocyclone discharge and suction compartments of at least 100 gpm, which guarantees the cones are never starved and the compartment is always fully processed. Undersize the bank and fluid short-circuits past the cones unprocessed; the solids it carries then load the centrifuge or force dilution. Feeding your compartment flows and cone rating into Rig IQ turns this from a rule of thumb into an exact cone count for the tank you actually have.
Cone capacities you size against
Cyclones are designed to run at a constant 75 feet of head at the inlet manifold, so at constant inlet pressure the flow through each cone is effectively fixed for a given fluid — which is what makes sizing a simple division. The standard ratings: a 10-inch desander cone passes about 500 gpm and makes a coarse cut (roughly 50% removal at 40–50 microns); a 4-inch desilter cone passes about 40 to 100 gpm — commonly around 60, high-capacity designs up to 100 — and cuts finer (about 50% at 15–20 microns); micro-fine cones pass about 15 gpm for the finest cut.
Because the desilter cone is small, a desilter bank needs many more cones than the desander to move the same flow — that is simply the price of the finer cut. This is also why head matters as much as cone count: run the manifold below 75 feet and every cone passes less than its rating and cuts coarser, so a bank that was correctly sized on paper is undersized in practice. Confirm the head first, then count the cones. Rig IQ will hold you to both.
Working the count
The method is one division per stage, rounded up. Take the total flow entering the suction compartment, divide by the per-cone capacity, and round up so the installed capacity clears 100% — then add a cone or two for the ‘preferably greater than 100%’ margin, and confirm at least 100 gpm of backflow. Do it per stage, because the desander and desilter draw from different compartments and have different cone capacities.
Say 800 gpm enters the desilter’s suction compartment. At 60 gpm per 4-inch cone that is 800 ÷ 60 = 13.3, so 14 cones just clears 100% (840 gpm, about 105%), and 16 cones gives a comfortable margin (960 gpm, about 120%). The desander handling the same 800 gpm at 500 gpm per 10-inch cone needs 800 ÷ 500 = 1.6, so 2 cones (1,000 gpm, about 125%). Add the 100-gpm backflow and the bank is correctly sized. Running those same inputs through Rig IQ gives you the count, the percentage of flow covered, and the head you need to hold — the full sizing, not just the cone number.
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: keep ≥ 100 gpm between discharge and suction compartments.
Measure against all flow into the suction compartment — not the circulation rate.
Size against the flow into the suction compartment, not the circulation rate — the cones must clear everything arriving there. Divide that flow by the per-cone capacity (500 gpm for a 10″ desander, ~60 for a 4″ desilter, at 75 ft head), round up past 100%, and keep ≥100 gpm backflow. And hold the head: below 75 ft, a paper-correct bank is undersized in the field.
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.
What flow rate should a hydrocyclone bank be sized for?
Not the circulation rate — the total flow of all fluids entering the cyclone's suction compartment, which includes mud-gun, transfer and return flows. The cones must process at least 100% (preferably more) of that, with at least 100 gpm of backflow between the discharge and suction compartments.
What is the flow capacity of a desander and desilter cone?
At the standard 75 feet of inlet head, a 10-inch desander cone passes about 500 gpm and a 4-inch desilter cone about 40–100 gpm (commonly ~60). Micro-fine cones pass roughly 15 gpm. Below 75 ft of head each cone passes less and cuts coarser, so the head must be held for the rating to apply.
