SLURRY GLOSSARY
Slurry Pump and Dredging Terms, Explained
Plain-English definitions of 90 terms engineers, operators and buyers use when selecting, running and maintaining slurry pumps and dredging equipment. Written by the team that has built them in the USA since 1984.
Abrasion
The gradual wearing away of pump and pipe surfaces by hard, sharp or coarse solids such as sand, rock and ore. Abrasion is the main driver of wear in slurry service and a key factor when choosing pump materials.
Acre
A unit of land area equal to 4,840 square yards (43,560 square feet). Lagoon, reservoir and pond cleanups are often scoped by surface acres.
Affinity Laws
Relationships that predict how a centrifugal pump’s flow, head and power change when speed or impeller diameter changes. Flow varies with speed, head with speed squared, and power with speed cubed.
Atmospheric Pressure
The pressure exerted by the weight of the atmosphere. At sea level it averages 101,325 pascals, or about 14.7 psi. It limits how high a pump can lift liquid by suction.
Auger Dredge
A dredge with an Archimedean screw (auger) set at a right angle to the suction pipe. The auger works like a wide, low-turbidity cutterhead, breaking up the target material and feeding it to the pump.
Autonomous Dredge
A dredge that operates independently using predefined inputs, with operators supervising remotely instead of driving it from on board.
Beach Restoration
Replacing sand and sediment lost to erosion with material gathered by dredging, then pumped onto the shoreline.
Best Efficiency Point (BEP)
The point on a pump curve where the pump runs at its highest efficiency for a given speed and impeller diameter. Operating close to BEP reduces wear, vibration and energy use.
Booster Pump
A pump added in line with a pipeline to restore pressure and extend how far slurry can be moved. Booster pumps let a dredge or process pump reach long discharge distances.
Brake Horsepower (BHP)
The actual power a pump draws from its driver (engine, electric motor or hydraulic motor) at the shaft. It is higher than hydraulic horsepower because no pump is 100% efficient, and it is used to size the drive.
Cavitation
The formation and collapse of vapor bubbles in a pump when pressure at the suction drops below the liquid’s vapor pressure. It causes noise, vibration, lost performance and damage to the impeller and casing.
Centrifugal Pump
A pump that uses a rotating impeller to add velocity to the fluid, which the casing converts into pressure. Most slurry and dredge pumps are heavy-duty centrifugal designs.
Close Coupled
A pump in which the impeller mounts directly on the drive shaft of the motor or engine. This keeps the unit compact and removes the need for a separate pump shaft and coupling alignment.
Construction Dredging
Dredging used to cut trenches and prepare the ground for tunnels, pipelines, foundations and other structures.
Critical Velocity
The minimum flow velocity at which solids stay suspended in a pipeline. Below it, solids settle on the bottom of the pipe and can plug the line; well above it, friction loss and wear climb, so lines are run just over critical velocity.
Cubic Meter (m³)
A unit of volume equal to a cube one meter on each side. To convert cubic yards to cubic meters, multiply by 0.7646.
Cubic Yard (yd³)
A unit of volume equal to a cube one yard on each side. Cubic yards = length (ft) × width (ft) × depth (ft) ÷ 27. To convert cubic meters to cubic yards, multiply by 1.308.
Cutter Hydraulic Pump Temperature
The case temperature of the hydraulic pump that drives the cutterhead. Watching it helps operators catch overload or cooling problems early.
Cutter Pressure
The hydraulic pressure at the cutterhead drive. A sudden rise can mean the cutter is overloaded or jammed in dense material.
Cutterhead
A rotating cutting tool at the suction end of a dredge that loosens compacted or hard material so the pump can pick it up. Equipped with cutting teeth for clay, hard-packed sediment and soft rock.
Density
Mass per unit volume, usually expressed in pounds per gallon. A gallon of water weighs more than a gallon of gasoline. Slurry density rises with solids content and directly affects pump power and friction loss.
Dewatering
Removing or displacing groundwater, surface water or process water from a worksite or from solids, most often by pumping or gravity. With dredged material it also means separating water from solids using settling ponds, geotextile tubes or mechanical presses.
Discharge Head
The head on the outlet side of a pump. It is made up of the discharge velocity head, the discharge friction head and the discharge static lift.
Discharge Pressure
The pressure in the discharge line, measured in pounds per square inch (psi). As discharge pressure changes, discharge head changes with it, so it is a quick indicator of what is happening in the line.
Dredge Advance
The forward movement of the dredge along the cut as material is removed.
Dredge Pump
Equipment that moves slurry from the dredging area into the pipeline by suction through turning impellers. Dredge pumps handle sand, gravel, high solids concentrations and debris. The EDDY Pump uses a large open rotor designed to move high solids and rocks.
Dredging
Removing sediment and debris from the bottom of water bodies. The material is disposed of at another location or reused, and is often pumped to a beach or marsh for restoration projects.
Dredging Depth
The total vertical distance between the water surface and the target material.
Effective Particle Diameter
The single or average particle size of a slurry containing a mix of particle sizes. It is used to calculate pump system requirements and overall pump performance.
Elevation
The rise of the discharge pipeline, usually measured from the water level to the highest point on the line. Steeper or higher elevation increases friction on the material and reduces velocity.
Environmental Dredging
Using a dredge to remove contaminated sediment from a body of water so the water can be restored and its capacity recovered.
Flooded Suction
A setup where the pump chamber is full of liquid because the pump sits below the liquid level, so liquid flows into it by gravity and no priming is needed. Common in tank, sump and process-plant arrangements.
Flow Rate
The volume of fluid a pump moves in a given time, usually in gallons per minute (GPM) or cubic meters per hour (m³/h). In slurry systems flow must stay high enough to keep solids suspended.
Friction Loss
The loss of pressure or head as slurry moves through pipe, hose and fittings, caused by the fluid’s viscosity near the pipe wall. It rises with flow velocity, pipe length and slurry density, and is a major part of total dynamic head.
Gear Temperature
The operating temperature of the gearbox. Peak operating temperature should be 160°F; higher temperatures can lead to premature wear and part failures.
Geotextile Tube
A large, permeable fabric tube filled with dredged slurry. Water drains through the fabric while the solids stay contained, which dewaters and stores the material.
GPM
Gallons per minute, the standard unit for flow rate in dredging and pumping applications.
Head
The height at which a pump can raise liquid, or more precisely the energy of a liquid relative to a reference point, expressed per unit weight. Head lets pump performance be described independently of liquid density.
Hydraulic Dredging
Removing sediment by mixing it with water and pumping the slurry through a pipeline to a disposal or processing area. Hydraulic dredges use suction, jetting, cutterheads or augers to bring material to the pump.
Hydraulic Motor
A motor driven by pressurized hydraulic oil that turns the pump shaft. Hydraulic motors deliver high torque in a compact package, and speed is adjusted by controlling oil flow.
Hydraulic Oil Temperature
The measured temperature of the hydraulic oil. Maximum oil temperature should be set between 160°F and 180°F, and minimum oil temperature at 70°F.
Hydraulic Power Unit (HPU)
The main driving component of a hydraulic system, made up of a motor, a hydraulic pump and a reservoir. It supplies pressurized oil to the hydraulic motor that drives the pump, so the pump can run remotely, such as on a dredge or underwater.
Hydraulic Pump Charge Pressure
The hydraulic charge pump supplies coolant to the system and keeps positive pressure in the main loop. The normal operating range is 350 to 380 psi.
Impeller
The rotating part of a centrifugal pump that transfers energy to the fluid, raising its pressure and flow. Slurry impellers use wide passages and thick, wear-resistant vanes. The recessed impeller on the EDDY Pump is what lets it excel at moving solids and slurry.
Jetting Ring
A ring of water jets near the suction inlet that agitates and loosens settled sediment so it can be drawn into the pump.
Ladder
The boom that extends from the front of a dredge. It is lowered below the water to reach the target material and carries the suction pipe and cutting device.
Lake and Lagoon Dredging
Removing the sediment and sludge that build up on the bottom of lakes and lagoons. It restores water volume, reduces odor and brings the basin back to its original capacity.
Liner
A replaceable wear layer, such as rubber or hardened metal, fitted inside a pump casing or pipe to absorb abrasion and extend service life.
Mechanical Dredging
Removing compacted material or debris with a physical tool, commonly a bucket or clamshell deployed from a crane or an excavator boom.
Mechanical Seal
A sealing assembly at the shaft that keeps pumped fluid from leaking along the rotating shaft. In slurry service seals face abrasive solids, so cooling and flush support are important.
Mining Dredging
Using dredging equipment to excavate gravel, sand, coal and mine tailings.
Non-Clog Pump
A pump with open passages so stringy material, debris and large solids pass through without blocking the impeller or casing.
NPSH
Net Positive Suction Head. NPSH available is the absolute pressure at the pump suction above vapor pressure; NPSH required is the minimum the pump needs to avoid cavitating. Available must exceed required.
Percent Solids (Concentration by Volume)
The share of a slurry made up of solids. Concentration by volume (Cv) is the volume of solids divided by the total volume of the mixture. Always check whether a figure is by weight or by volume, because the two are not interchangeable.
PLC (Programmable Logic Controller)
A ruggedized computer used for pump control. The PLC reads connected sensors and input devices, processes the data and triggers outputs based on pre-programmed parameters.
Positive Displacement Pump
A pump that moves a fixed volume of fluid per cycle, such as diaphragm, piston and progressive cavity types. They can build high pressure but are more sensitive to solids and wear than centrifugal designs.
Pressure
The force a liquid exerts on the walls of a tank or pipe. In the USA it is measured in pounds per square inch (psi); the metric system uses bar, where one bar is about one standard atmosphere.
Pressure Drop
A decrease in pressure along a pipe or through a component, caused by friction and flow disturbance, which turns potential energy into heat.
Priming
Removing air from the pump volute and suction line by filling them with liquid so the pump can move fluid. A standard centrifugal pump cannot pump air, so it must be primed before it starts.
Pump Curve
A graph (also called a pump performance curve) showing a pump’s head, efficiency, power and NPSH required across a range of flows at a given speed. It is used to find the head a pump delivers at a given flow rate.
Pump Speed
How fast the impeller turns, which is the motor RPM. Speed must be increased to hold slurry velocity as discharge distance grows. Some electric motors run at fixed RPM; others can be adjusted with a VFD.
Radial Flow
Flow in which a centrifugal pump discharges fluid radially, at right angles to the pump shaft.
Recreational Dredging
Maintaining, deepening and expanding lakes and other waters used for swimming and boating. Without maintenance dredging, accumulated sediment makes the water shallower and disrupts boat travel.
Sediment
Fragmented, naturally occurring material such as silt, sand and gravel found settled at the bottom of a body of water or other liquid.
Self-Priming Pump
A centrifugal pump with a built-in priming unit that removes air from the pipeline and volute, so it can start and restart without manual priming. Useful for trailer-mounted, standby and sump work.
Service Water Pressure
The pressure of the service (flush) water supplied to the pump, measured in psi. It must be kept above the dredge discharge pressure.
Sludge
A thick, semi-solid mixture left over from treatment, settling or industrial processes. Sludge has high solids content and often high viscosity, which makes it hard to pump.
Slurry
A mixture of liquid, usually water or oil, and solid particles such as sand, cement or coal ash that can be pumped. Slurries vary widely in particle size, density, abrasiveness and viscosity.
Slurry Transport
Moving solids through a pipeline as slurry, from hydraulic conveying and conventional lean slurry to high-concentration slurry disposal.
Smart Pump
A pump that connects to other devices so it can be operated remotely and can send diagnostic information about its performance.
Soft Start
A device used with electric motors to temporarily reduce load, torque and the electrical current surge at start-up, which helps extend motor life.
Solids Handling Pump
A pump engineered to pass solids, from fine particles to large debris, without clogging or wearing out quickly. The term covers non-clog, vortex and heavy-duty slurry designs.
Specific Gravity
The ratio of a fluid’s density to the density of water. Water is 1.0, so a slurry with a specific gravity of 1.5 is 50% heavier than water. Higher specific gravity raises the power a pump needs.
Static Lift
The vertical distance between the point of discharge and the surface of the water being pumped (also called terminal elevation).
Submersible Pump
A pump, with its motor or hydraulic drive, that operates underwater. Submersible slurry pumps work in sumps, ponds and lagoons without needing to be primed.
Suction Head
The resistance to slurry flow on the suction side of the system, expressed in feet of water.
Suction Lift
The vertical distance from the liquid surface down to the pump centerline when the pump sits above the liquid. Practical suction lift is limited by atmospheric pressure and NPSH.
Surface Feet Per Minute
The speed of a point on a surface, such as the outside diameter or eye of the impeller, expressed in feet per minute.
Tailings
Waste material left after valuable minerals are extracted from ore, usually pumped as slurry to a tailings dam or storage facility.
Ton
A unit of weight. A US (short) ton equals 2,000 pounds. Dredge production is often quoted in tons of material per hour.
Total Dynamic Head (TDH)
The total head a pump must overcome: the sum of discharge head, suction head and friction loss. TDH is the key number for choosing a pump from its curve.
Turbulence
Disturbed, swirling flow produced by velocity and friction in the pipeline. Some turbulence helps keep material suspended so it travels efficiently through the line.
Vacuum
A pressure below atmospheric, measured in inches of mercury. It is commonly used to describe the pressure at the pump’s suction.
Variable Frequency Drive (VFD)
An electronic controller that adjusts an electric motor’s speed by varying the frequency of its power supply, so pump flow and head can be matched to demand with soft starts.
Viscosity
A fluid’s resistance to flow, or the “thickness” of the medium. Thick fluids such as sludge, paste and black liquor need more power and pump designs built for high viscosity.
Volute
The spiral-shaped casing of a centrifugal pump that collects fluid thrown off the impeller and slows it down, converting velocity into pressure.
Vortex Pump
A pump with a recessed impeller that creates a swirling vortex in the casing, so most solids pass without touching the impeller. Used for stringy or fragile solids.
Water Hammer
A pressure surge caused when moving fluid suddenly changes direction or stops, for example when a valve closes quickly. It can damage pipes, fittings and pumps.
Well Point
A shallow dewatering system of small-diameter pipes driven into the ground and connected to a header and suction pump to lower the groundwater level around an excavation.
PUT THE TERMS TO WORK
Free engineering calculators
Use the numbers behind the terms. Each tool is free to use on eddypump.com.
Total Dynamic Head Calculator
Work out the head your system demands so you can size a pump from its curve.
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NPSH Available Calculator
Check your suction margin and avoid cavitation before it damages the pump.
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Slurry Density Calculator
Convert between percent solids, specific gravity and slurry density.
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Related equipment
See the equipment behind the terms.
Slurry Pumps
Non-clog slurry pumps for abrasive, high-solids pumping.
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Dredging Equipment
Dredge pumps, cutterheads, sleds and complete dredging systems.
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Hydraulic Power Units
USA-made HPUs to drive dredge and slurry pumps.
Learn more →
Booster Pumps
Extend your discharge distance with in-line boosters.
Learn more →
Frequently Asked Questions
What is a slurry?
A slurry is a mixture of liquid, usually water, and solid particles that can be pumped. Sand, mine tailings, drilling cuttings, sludge and dredged sediment are all common examples.
How is a slurry pump different from a water pump?
A slurry pump is built to handle solids and abrasion. It uses larger passages, thicker wear parts and stronger materials than a clean-water pump, which would clog or wear out quickly in slurry service.
Why does specific gravity matter when choosing a pump?
Heavier slurries need more power to move and create more friction in the pipeline. Knowing the specific gravity and percent solids lets you size the pump and drive correctly.
What is TDH and how do I calculate it?
Total dynamic head is the sum of the discharge head, suction head and friction loss. Our TDH calculator walks you through each input.
What is the difference between suction head and discharge head?
Suction head is the resistance to flow on the suction side of the pump. Discharge head is the head on the outlet side, made up of discharge velocity head, discharge friction head and static lift.
What happens if NPSH available is too low?
The pump cavitates. Vapor bubbles form and collapse inside the pump, causing noise, vibration, reduced flow and damage to the impeller and casing.