Desander selection should follow the shale-shaker and degasser, precede the desilter, and remove 45–74 µm solids from rotary-drilling slurry while protecting pumps, valves and downstream separation equipment [S1][S5].
Define the Slurry Load and Separation Duty
Desanders are hydrocyclone units that remove sand and silt by centrifugal separation, with denser, larger particles moving to the underflow while the cleaned liquid and finer particles leave through the overflow [S1][S8]. In a rotary drilling rig, this second-stage separation follows coarse solids removal by the shale shaker and degasser, but precedes a desilter intended for finer solids [S1][S5].
The first sizing calculation is the measured peak slurry flow, not average return rate. The RMT200 is listed with a maximum capacity of 200 m³/h [S4][S7]. The right desander should be selected according to slurry flow rate, ground conditions, solids concentration, and required separation size [S2].
Ground conditions and circulating-fluid properties define the solids challenge. Selection inputs include slurry flow rate, solids concentration, particle-size distribution and required separation size [S2]. A desander nominally targets 44–74 µm material, while one RMT200 slurry package specifies a d50 cut point of 0.06 mm, equivalent to 60 µm [S1][S4].
For a slurry-separation system, the cut point should be stated as a defined particle-size metric rather than as a general removal claim. The RMT200 uses d50 = 0.06 mm, and the AMT500 rotary-drilling package also lists 0.06 mm at d50 [S4][S9]. These figures describe the separator target, not proof that every particle at that diameter will be removed.
Compare Hydrocyclone Size Against Operating Capacity
The smaller cone offers a tighter nominal separation target and compact footprint, but requires more cones or units to pass the same peak flow.
Cyclone diameter alone does not determine performance, because feed flow, differential pressure, fluid density, viscosity and particle concentration also affect classification.
Calculate Cone Count and Package Capacity
Cone count should be calculated from the required peak flow, then checked against the package rating.
Do not select by pump horsepower alone. A 45 kW main pump is paired with the RMT200 package rated for 200 m³/h, and its complete power is listed as 48 kW after adding two 1.5 kW vibration motors [S4][S7]. The RMT200 is listed with a transportation dimension of 4.0 m [S4][S7].
Match the Unit to a Rotary Drilling Application
Hydrocyclone desanders suit continuous slurry recycling on rotary rigs, bored piles, continuous concrete walls and slurry-shield tunnelling, where separated solids must be removed before they damage pumps, valves or reuse equipment [S4]. The equipment belongs within the complete rotary drilling rig solids-control train rather than operating as an isolated separator.
For a drilling mud system, the normal sequence is shale shaker, degasser, desander and desilter, with the desander removing abrasive particles in the 45–74 µm band [S5]. A compact 8-inch arrangement becomes more attractive when the target is 37–67 µm and the available deck area is restricted [S5].
For bentonite slurry used in rotary-drilled foundation work, the package can combine a desander and desilter, as illustrated by the RMT200 designation [S4][S7]. Such a combined arrangement is useful where the rig requires both medium-solid removal and treatment of a finer solids fraction, but its duty must still be divided between the two separation stages rather than treating the combined package as one uniformly sized cyclone.
Check Fluids, Wear Parts and Operating Constraints
Desander performance must be checked using the actual slurry rather than water.
Hydrocyclone internals require wear-resistant construction. The Brightway design uses polyurethane cyclone cones and Q235B steel bodies, with an abrasion-resistant coating treatment comprising abrasive blasting, epoxy zinc-rich primer, epoxy micaceous iron intermediate paint and polyurethane finish paint [S3]. Its optional bottom shaker uses an API 120, 150 or 175 mesh screen and provides liquid recovery from the underflow solids [S3].
Electrical and environmental requirements also affect final sizing. Published BWCSQ configurations include explosion-proof controls and IEC, UL, ATEX and CE certification options, with a design temperature range of −40 to 50 °C and noise control of 75–85 dBA [S3]. These are procurement and installation checks, not substitutes for verifying the duty on the selected unit.
Specify and Verify the Desander Package
A complete purchase specification should state peak slurry flow in m³/h, required cut point and reporting basis such as d50, cyclone diameter and quantity, operating differential pressure, underflow handling method, installed pump power, unit weight and envelope [S1][S4][S5]. The RMT series illustrates the commercial range: RMT100A handles 100 m³/h with a 40 µm d50, while RMT150, RMT200 and RMT250 handle 150, 200 and 250 m³/h at 60 µm d50 [S4].
Factory acceptance should use the agreed slurry density and viscosity. A defensible test compares inlet flow with the specified 240 m³/h for a 2 × 10-inch unit, 200 m³/h for RMT200, or 500 m³/h for RMT500, then checks underflow solids discharge and overflow recovery [S3][S4]. It should also confirm that the 30 psi common operating differential pressure can be maintained at the selected flow and that cyclone liners, manifold connections and the bottom shaker are correctly installed [S5].
Track two operating signals after commissioning: differential pressure across the cyclone bank and the solids concentration or underflow consistency from the separator. Rising differential pressure can indicate plugging or slurry-condition changes, while changing underflow consistency indicates that the selected cut point no longer matches the actual solids load. Either signal calls for sampling the particle-size distribution before changing cone diameter or adding capacity.