Valve and Airlock Selection for Mining and Mineral Plants

Abrasive minerals destroy valves, and they do it predictably. Silica sand, alumina, iron ore fines and crushed aggregate erode seats, blades and rotor tips within months, and the first symptom is not failure but leakage: a gate that no longer seals, a rotary valve whose clearance has grown until half the conveying air goes the wrong way.

The forces are also larger than catalogue selection suggests. A knife gate under a loaded bin has to cut through a column of material, not swing in clear air, and a blade selected on nominal capacity bends on the first full bin.

Oversize is the other recurring fault. A screen that passes a tramp particle, a lump that formed in a damp bin, or a bolt from upstream maintenance jams a blade that handled the nominal product without trouble, and the jam is what breaks the actuator.

A valve whose wear life is known rather than discovered, with wear concentrated in replaceable liners, blades and rotor tips, and with access that lets a change happen in a planned shutdown instead of an unplanned one.

A clearance or seal condition that is measured as a performance indicator, so the plant knows the valve is leaking before the conveying system tells it the hard way.

The same duty in a pet food plant is governed by fat on the seal face and by changeover count per shift, not by abrasion, and a hard-faced blade helps nothing there.

Selection starts with the particle size distribution including the top size, and with the honest version of it: what the screen passes when it is worn, not what it passes when it is new.

For bins and chutes, knife and roller gates with replaceable liners are the normal answer, specified with the blade treated as a scheduled change rather than a failure. Where the blade has to cut through material under a head, the actuator and the frame are sized for that, not for the free swinging case.

Where the valve is a pressure boundary, a rotary valve with a hardened or tipped rotor in a lined housing is used, and the tip clearance is logged. Clearance growth is the measurable form of wear, and a trend line gives weeks of warning.

Diverter valves in abrasive service wear at the junction, not at the actuator, so the liner at the point where the stream changes direction sets the interval. A diverter chosen for its actuator and lined as an afterthought wears through at the one place nobody specified.

• Top size and worn screen output used for sizing, not the nominal distribution.
• Wear concentrated in liners, blades and tips that are listed as consumables.
• Gate actuators and frames sized for cutting through a loaded column.
• Rotor tip clearance logged as a performance indicator with a trend.
• Diverter liners specified at the junction, which is where the stream turns.
• Spares held locally, with the change procedure written before it is needed.

• Abrasiveness and particle angularity, which decide liner material: hardened steel, ceramic tile, or a replaceable rubber depending on impact angle.
• Top particle size and credible tramp material, which decide the opening and the jam case.
• Head of material above a gate, which decides the closing force and the frame.
• Service access, because a valve that needs the chute cut to change a blade will be run past its life.
• Moisture content, since damp mineral builds up and turns a sliding surface into a sticking one.
• Pressure duty, which decides whether the valve has to seal at all or only has to stop flow.