STAGE 02 · SAND & SILT

Hydrocyclones — desanders & desilters

No moving parts — they live or die on feed head

Hydrocyclones are the only major solids-control equipment with no moving parts — just pressure and geometry. Mud is pumped into a cone tangentially, spins hard, and centrifugal force throws solids to the wall and down to the apex while clean fluid spirals up and out the top. Because nothing breaks, they fail silently: when they stop cutting, nothing alarms, and the only symptom is a slow, expensive rise in dilution.

What it does

Remove sand- and silt-sized drilled solids (roughly 15–74 µm) that the shaker passed, in two stages — desanders for the coarse fraction, desilters for the fine — before the centrifuge.

How it works

Feed enters the cone tangentially under pressure and is forced into a tight spiral. The centrifugal field — many times gravity near the wall — drives denser solids outward and down to the apex (underflow) while lighter fluid reverses into an inner spiral and exits the overflow at the top. The strength of that spin is set almost entirely by feed head; lose the head and you lose the separation even though fluid still flows.

Key components

Cone bodyThe separation chamber; diameter sets the cut — large desander cones for sand, small desilter cones for silt.

Tangential feed inletInjects the slurry to start the spin; fed from a dedicated centrifugal pump.

Vortex finder (overflow)Carries clean fluid out the top in the inner spiral.

Apex (underflow nozzle)Discharges the concentrated solids; its size sets the underflow and must match the load.

Feed manifold & pumpDelivers the head the cones live on; a worn impeller is the most common hidden cause of failure.

Operating parameters

Parameter	Range	Notes
Feed head	≥ 75 ft	Below ~75 ft the cone can't form an air core
Desander cones	6–12″	Cut ~40–74 µm, high volume per cone
Desilter cones	4″ (and smaller)	Cut ~15–40 µm, many cones in parallel
Bank sizing	100–125% of flow	Process the full circulating rate with margin

Health indicators — what good looks like

Every apex showing a fine umbrella spray with a visible air core.
Manifold pressure holding at design (≥ 75 ft of head).
Underflow solids-laden, not thin and watery.
LGS falling across the section the cones should control.

Common problems & how to fix them

The failures this machine throws, each with a full field fix:

Cone roping

Rope discharge, no air core — fines recirculate.

Troubleshoot →

Cone plugging

A dead, silent cone — no discharge at the apex.

Troubleshoot →

Low underflow

Thin, watery discharge — removes little.

Troubleshoot →

Field tips

Calculate feed head whenever cones underperform: h = 19.2 × p ÷ ρ. Below ~75 ft is your problem — don't eyeball it.
Walk the bank and read every apex: umbrella = cutting, rope = low head or overload, dry = plugging.
The most common hidden cause of roping is a worn feed-pump impeller bleeding off head over days.
Run the desander before the desilter — take out the sand first so the small cones aren't flooded.

Want this machine read on your rig?

Send your shift data — we evaluate the train against API RP 13C and tell you exactly what to change. Remote, vendor-neutral.

Request a remote evaluation →