When it comes to pumping and transporting slurries, one of the most important distinctions is whether you’re dealing with a settling or non-settling slurry. This difference can drastically impact your equipment selection, pipe design, and overall system efficiency.
But what exactly does it mean—and why does it matter?
What Is a Slurry?
A slurry is a mixture of solid particles suspended in a liquid, typically water. They’re common in industries like mining, wastewater, food processing, and chemical manufacturing.
The behavior of a slurry depends heavily on the type, size, and concentration of the solid particles—and that brings us to two key types:
1. Settling Slurries
Definition:
Settling slurries contain coarse, heavy particles that tend to fall out of suspension if the flow slows down or stops.
Key Characteristics:
- Contains larger particles (often > 100 microns)
- Particles tend to settle at the bottom of the pipe
- Requires higher flow velocities to keep solids in suspension
- Common in mining, sand pumping, and dredging applications
Challenges:
- Risk of pipeline blockages or sediment buildup
- Requires careful velocity control and system design
- Abrasive wear on pumps and pipes
Example:
A mixture of water and crushed rock from a mineral processing plant
2. Non-Settling Slurries
Definition:
Non-settling slurries contain fine, often colloidal particles that stay suspended in the liquid due to Brownian motion or viscosity.
Key Characteristics:
- Fine particles (often < 50 microns)
- Appears more like a thick, consistent fluid
- Minimal settling, even at low flow velocities
- Often behaves like a Newtonian or slightly non-Newtonian fluid
Challenges:
- May have higher viscosity
- May require positive displacement pumps
- Can be difficult to dewater or separate
Example:
A slurry of clay particles in water or lime milk in wastewater treatment
Why the Difference Matters
Choosing the right pump, pipe diameter, and flow rate all depends on whether the slurry settles or not:
| Factor | Settling Slurry | Non-Settling Slurry |
|---|---|---|
| Pipe Velocity Needed | High (to prevent settling) | Lower (solids remain suspended) |
| Pump Type | Centrifugal or slurry pumps | Peristaltic, diaphragm, PC pumps |
| Wear & Abrasion | High | Moderate to low |
| Flow Behavior | Two-phase (solids + liquid separate) | Homogeneous or pseudo-homogeneous |
| Maintenance Risk | Blockages possible | Less likely |
How to Tell What You’re Dealing With
- Visual inspection: Settling slurries often separate in a container after standing still
- Particle size analysis: Use d50/d85 data to estimate settling potential
- Lab tests: Rheology tests and settling rate measurements can confirm slurry behavior
Understanding whether your slurry is settling or non-settling is critical for designing an efficient and reliable pumping system. It influences everything from pump choice to flow velocity to pipeline wear.
Need help identifying your slurry type or selecting the right pump? Our team of pump experts is here to help.
