Settling Velocity Calculation
Stokes’ Law and Particle Capture
A particle is captured when its settling velocity exceeds the surface loading rate. Stokes’ law gives the settling velocity for discrete particles.
Settling Velocity Calculation
For discrete, non-flocculating particles in the laminar regime, Stokes’ law relates settling velocity to particle diameter, the density difference between particle and water, gravity and water viscosity.
The design rule is simple: set the surface loading rate below the settling velocity of the smallest particle you must remove, and it will be captured on a plate.
Real wastewater solids often flocculate, settling faster than Stokes predicts — which is why coagulation/flocculation upstream is so effective and why pilot data or R+F experience refines the design.
v_s = g (ρ_p − ρ_w) d² / (18 μ)Stokes’ settling velocity; d = particle diameter, μ = dynamic viscosity, ρ = densities.
Capture if v_s > SLRParticles settling faster than the surface loading rate are removed.
Basis
Free Sizing Check
Try the interactive Plate Settler Sizing Calculator, or send us your flow and water-quality data for a preliminary sizing at no cost.
Key Considerations
Flocculation
Larger flocs settle much faster — condition solids to raise settling velocity.
Temperature
Cold water is more viscous, slowing settling — derate accordingly.
Design Link
Choose SLR from the target particle’s settling velocity.
Request an Engineering Assessment
Our engineers will review your application, flow rates, and water quality data to recommend the optimal plate settler configuration.