How to Select a Ball Valve for Slurry Service | Solids, Full Bore, Seat Design

Specify the Slurry With Numbers

Do not send an RFQ that only says “slurry service.” At minimum, give the valve supplier these values:

• solids concentration in wt.% or vol.%
• D50
• D90
• maximum particle size
• particle material or mineral
• particle hardness if known
• particle density or specific gravity
• normal and maximum flow
• upstream and downstream pressure
• maximum differential pressure
• normal, design, startup, and shutdown temperature
• cycles per day or year
• longest shutdown period

These numbers tell the supplier whether the main risk is abrasion, particle trapping, settling, high torque, or chemical attack.

Use wt.% and vol.% Correctly

Weight concentration and volume concentration are not the same.

Assume 100 kg of slurry contains 20 kg of mineral solids with a specific gravity of 2.65 and 80 kg of water.

So “20% solids” is not enough information. The RFQ should say either 20 wt.% or 20 vol.%.

This is a calculation example only. Actual volume concentration changes with particle and liquid density.

Use D50, D90, and Maximum Particle Size Together

D50 is the size below which 50% of the stated cumulative particle distribution falls. D90 is the size below which 90% falls. The distribution may be based on mass, volume, or particle number, so the measurement basis should also be stated.^[1]

Laser diffraction is widely used for fine-particle sizing. ISO 13320 covers particle-size analysis by laser diffraction.^[2]

Useful conversions:

• 100 μm = 0.10 mm
• 500 μm = 0.50 mm
• 1,000 μm = 1.00 mm

Do not select a valve from D50 alone.

Both slurries have the same D50, but Slurry B contains much larger particles. A 2 mm particle creates a very different closing problem from a 0.3 mm particle because it has a greater chance of becoming trapped between the ball and seat.

Check Particle Hardness and Shape

Hard particles can damage polymer seats, metal seats, and the ball surface.

Common abrasive solids include:

• quartz
• silica
• sand
• ore particles
• ash
• metal oxides
• catalyst particles
• mineral tailings

Fine particles are not automatically easy service. Small hard particles can remain suspended and repeatedly enter the sealing area.

Angular particles usually cut a surface more aggressively than rounded particles of similar size.

ASTM G75 provides the Miller Number for comparing slurry abrasivity and the SAR Number for comparing how materials respond to a particular slurry.^[3]

Check What Happens When Flow Stops

For settling slurry, normal flowing conditions may not be the worst condition.

Check whether the solids:

• settle within minutes or hours
• remain loose after settling
• compact into a dense bed
• form scale
• crystallize
• harden when dry

Particle density, size, liquid viscosity, and particle shape all affect settling behavior.^[4]

Compare two valves carrying the same slurry:

• Valve A: operates every 4 hours.
• Valve B: may remain closed for 30 days.

Valve B may have fewer annual cycles but a harder first movement because solids have had much more time to settle, compact, or crystallize.

Keep Velocity Between Settling and Erosion

Slurry velocity has two opposite risks:

• too high: more erosion
• too low: more settling

There is no single correct velocity for every slurry. The acceptable range changes with particle size, particle density, solids concentration, pipe diameter, liquid properties, and how thick the slurry is.

High local wear is most likely where flow:

• passes through a smaller opening
• changes direction
• hits a seat edge
• passes a partly open valve
• expands after a restriction

A valve closing through a settled bed has a much higher chance of trapping solids than a valve closing through a well-suspended slurry.

Use Full Bore for Isolation

For on/off slurry isolation, full bore is usually preferred because it gives solids a larger and less restricted path.

The effect of bore reduction is larger than it first appears.

Reducing a circular bore from 100 mm to 80 mm cuts flow area by about 36%. At the same incompressible volumetric flow rate, velocity through the 80 mm opening is about 56% higher.

This does not mean every 80 mm bore will erode quickly. It shows why actual bore diameter matters in abrasive service.

Do not rely only on “full port” or “full bore.” For piggable or coarse-solids service, specify:

• DN or NPS
• pipe schedule
• actual pipe ID
• required minimum clear valve bore

The dimensional difference between full-bore and reduced-bore ball valves should be checked from the actual bore, not only nominal valve size.

Full bore does not stop solids from entering the seat pockets or body cavity.

Choose Polymer or Metal Seats by Wear Risk

Common polymer seat materials include PTFE, reinforced PTFE, PEEK, and other engineered polymers.

A hard particle trapped between a polymer seat and the ball can cut the seat, embed in it, or scratch the ball.

Do not assume reinforced PTFE or PEEK is automatically suitable for slurry. Check temperature, chemistry, particle hardness, pressure, and cycling.

The construction of a forged soft-seated ball valve can be compared with metal-seated construction when the slurry is mild enough for a polymer sealing surface.

Metal seats are often considered when abrasion or temperature makes polymer seats unsuitable. A forged metal-seated ball valve may use hardened or coated ball and seat surfaces for more severe service.

“Metal seated” is not a complete specification. Check:

• ball material
• seat material
• coating or hard-facing
• coating thickness
• surface finish
• seat loading
• required leakage rate
• maximum differential pressure

Metal seat does not automatically mean zero leakage. The purchase specification should define the test method, test pressure, test medium, pressure direction, and allowable leakage.

Keep Solids Out From Behind the Seat

A seat may still be in good condition on its front sealing face while solids behind it stop it from moving correctly.

Check whether particles can reach:

• seat springs
• secondary seals
• seat carrier clearances
• pressure-responsive seat areas

If those areas fill with solids, the seat may stick and lose correct contact with the ball.

Ask the supplier one direct question:

Can slurry get behind the seat, and how does the design deal with it?

Use Scraping Only When It Solves a Real Problem

Scraping or wiping seats can remove deposits from the ball as it rotates.

They can be useful for:

• sticky slurry
• scale-forming media
• pigments
• pulp
• mineral deposits

The scraping edge is itself a wear surface. More contact also means more friction.

Check scraping geometry together with:

• maximum particle size
• ball coating
• seat coating
• cycle frequency
• actuator torque

Protect the Whole Wear Path

Do not protect only the ball.

In abrasive slurry, wear may occur at:

• ball surface
• seat edge
• port edge
• body transition
• downstream body wall
• downstream reducer

Possible hard-facing systems include:

• tungsten-carbide-based coatings
• chromium-carbide-based coatings
• cobalt-alloy hardfacing
• ceramic surfaces

Do not select a coating from hardness alone. Check:

• coating material
• application process
• thickness
• bond to the base material
• finished surface
• chemical compatibility

A coating can fail by gradual wear, chipping, or corrosion underneath it. A harder coating does not fix poor adhesion or chemical attack under the coating.

Control Solids in the Body Cavity

Slurry can move around the outside of the ball and settle in:

• the bottom of the body
• seat pockets
• trunnion areas
• bearing areas
• drains and vents

Review the valve cross-section and identify where solids can remain after the liquid stops moving.

Cavity fillers can reduce open volume around the ball in some services, but the filler must still tolerate pressure, temperature, chemistry, and abrasion.

Solids buildup and cavity overpressure are different problems. Some closed ball valves can trap liquid between their seats. If that liquid heats up, cavity pressure can rise. The seat arrangement must provide the correct pressure-relief path.

The mechanism is explained in more detail in this article on ball valve cavity pressure and thermal expansion.

If flushing is used, specify:

• flush fluid
• available pressure
• connection size
• flow direction
• flush timing

A flush port that plugs or cannot move the settled solids has little practical value.

Choose Floating or Trunnion by Load and Internal Design

In a floating ball valve, differential pressure moves the ball slightly toward the downstream seat.

In a trunnion-mounted valve, the ball is mechanically supported and the seats are commonly spring- and pressure-loaded.

Trunnion construction becomes more common as size, pressure, ball weight, and seat load increase.

It does not automatically make the valve suitable for slurry.

Check whether solids can reach:

• seat pockets
• bearings
• lower trunnion areas
• springs
• secondary seals

A metal-seated trunnion ball valve should therefore be judged by its internal solids-handling design, not only by the trunnion label.

Size the Actuator From Worst-Case Torque

Do not size a slurry-valve actuator from clean-service torque alone.

Check torque with:

• maximum differential pressure
• dirty seats
• settled solids
• scale
• packing friction
• temperature extremes
• long idle periods

A quarter-turn valve does not require the same torque through the full 90° stroke.

• Breakaway torque: torque needed to start movement.
• Running torque: torque during travel.
• Reseating torque: torque near full closure.

The valve torque curve should be compared with actuator output through the complete stroke.

For a pneumatic actuator, use minimum guaranteed air pressure at the actuator rather than normal plant-air pressure.

A larger actuator is not a cure for a blocked valve. Maximum actuator output should also stay below the stem and drive-train limits. Check operating torque against maximum allowable stem torque.

Do Not Throttle Slurry With an Isolation Ball Valve

A standard isolation ball valve should normally operate fully open or fully closed.

When it stays partly open, the small opening creates a high-velocity slurry jet that can attack:

• ball edge
• seat edge
• body
• downstream pipe

Valve damage from operation outside the intended throttling range can include high-velocity erosion, cavitation, and vibration.^[5]

If the process needs continuous control, evaluate a purpose-designed V-port, segmented-ball, or other severe-service control valve.

Check Corrosion and Temperature Separately From Abrasion

A material can resist corrosion and still wear quickly in abrasive slurry.

Check:

• pH
• chlorides
• acids
• alkalis
• process additives
• particle hardness
• flow velocity
• temperature

Abrasive particles can remove protective surface films from corrosion-resistant metals, repeatedly exposing fresh metal.

Temperature can also change:

• polymer-seat strength
• packing friction
• metal clearances
• coating stress
• slurry viscosity
• scaling or crystallization

A hot slurry that flows freely during production may become thick or hard after cooling. Check startup and shutdown temperature, not only normal operating temperature.

Separate Pressure Class From Differential Pressure

Pressure class does not tell you the pressure difference across the valve.

ASME B16.34 uses pressure-temperature ratings. Class 300 or Class 600 is not one fixed allowable pressure for every material and temperature.^[6]

The same pressure-class valve can therefore see very different seat loads and operating torque.

Give the supplier:

• normal upstream pressure
• normal downstream pressure
• maximum differential pressure
• differential pressure during opening
• differential pressure during closing

Count Both Cycles and Idle Time

These are calendar examples, not service-life limits.

A valve operating 50 times per day moves across the sealing interface about 18,250 times per year. A valve operating only twice per day sees about 730 cycles.

But low cycle count can still be difficult if the valve remains stationary long enough for slurry to settle or harden.

Always specify both:

• cycles per day or year
• longest expected idle period

Compare Valve Types by the Main Failure Risk

Use the Failure Pattern to Find the Problem

Inspect the valve before increasing actuator size.

Check the Installation Before Ordering

Review:

• pipe slope
• low points
• dead legs
• valve orientation
• drainage
• flush access
• maintenance space

Use the valve cross-section and the expected settling direction to identify where solids will collect.

Also plan commissioning. New piping may contain weld debris, rust, mill scale, sand, or other material larger than the normal process solids. That debris can damage a new seat before normal production starts.

Send This Data in the RFQ

A complete inquiry could look like this:

These are example values, not recommended limits.

Ask the supplier to return:

• seat cross-section
• ball and seat materials
• coating specification
• minimum clear bore
• valve torque curve
• actuator output curve
• cavity and seat-pocket details
• cavity-pressure relief method
• flush arrangement
• expected wear parts

Use These Supplier Questions

1. How does the seat handle our maximum particle size?
2. Can particles get behind the seat?
3. Where can solids collect inside the valve?
4. Which surfaces are protected from abrasion?
5. How was dirty-service torque calculated or tested?
6. What happens after the valve remains idle for our maximum shutdown period?
7. Which part normally wears first?
8. Can that part be repaired or replaced?
9. What similar slurry has used the same seat and coating design?
10. What maintenance interval was achieved in that service?

Use Standards for Qualification, Not Slurry Life

ASME B16.34 covers pressure-temperature ratings, materials, dimensions, testing, marking, and related requirements for applicable industrial valves. ASME currently lists B16.34-2025.^[6]

For pipeline and piping valves used in petroleum and natural-gas service, API Specification 6D may apply. API identifies the 25th edition and later addenda.^[7]

API lists API 608 Seventh Edition, published April 2, 2025, for metal ball valves and API 598 Eleventh Edition, published February 8, 2023, for valve inspection and testing.^[8]

ISO 5208 covers pressure testing of metallic industrial valves and closure-tightness verification.^[9]

A valve can pass its specified shell and seat tests and still fail early in slurry. Standard factory tests do not reproduce months of particle abrasion, settled solids, repeated slurry cycling, or long shutdowns.

Plan the Wear Parts and Life-Cycle Cost

For severe slurry, identify which part is expected to wear first.

Possible wear parts include:

• seats
• ball coating
• scraper edges
• liners
• sleeves
• packing

Check whether the part can be replaced in the field, whether the ball can be recoated, and whether matched ball-and-seat sets are required.

For metal-seated valves, a defined seat, coating, leakage-test, and repair plan is more useful than assuming the valve will run indefinitely without wear.

Compare total cost, not only purchase price:

• valve
• actuator
• wear parts
• recoating
• maintenance labor
• flushing
• valve removal
• production downtime

Finally

Approve a slurry ball valve only after the actual process numbers are known. Record wt.% or vol.% solids, D50, D90, maximum particle size, particle density, maximum ΔP, temperature, cycle count, and longest shutdown. A 100 mm bore reduced to 80 mm cuts flow area by about 36% and raises local velocity about 56% at the same flow rate, so bore size can materially change erosion risk. Then verify seat-pocket protection, cavity buildup, dirty-service torque, minimum actuator supply pressure, stem torque limit, flushing method, expected wear parts, and service history from a similar slurry.