The valve under a silo or hopper is one of the most consequential specifications on a bulk solids plant. It controls the entire discharge, it is difficult to access, and if it is wrong the symptoms — bridging, flooding, erratic flow, rapid wear — appear immediately and are expensive to correct. Yet it is often chosen last, from a catalogue, on bore size alone.

Before any valve is discussed, four material properties decide whether the outlet will work at all:

A cohesive material that arches will do so regardless of which valve is fitted. Replacing the valve does not fix a hopper that cannot discharge.

Every material has a critical arching dimension: the span it can bridge across and support itself. The outlet must be larger than that, with margin. This is a hopper design question, but it constrains the valve: a valve that restricts the outlet below the critical dimension will cause bridging even though the hopper itself is adequate.

This is one argument for valve types that present a full circular bore when open, and against designs whose mechanism occupies part of the flow area.

This is the question that most often goes unasked. A valve can do one of three jobs, and the type that does one well usually does the others badly:

Using the wrong category creates the classic failures: a butterfly valve throttled to control flow destroys its seat; a rotary valve asked to give precise control delivers erratic output and wears fast.

If the material arches, the answer may be vibration, aeration, or an activated hopper — not a valve. Where a discharge aid is used, the valve must tolerate it: vibration loosens flange bolts and fatigues a sleeve, and aeration changes the material's behaviour at the valve seat.

A discharge valve sits in an awkward place and will need attention. Two practical requirements: the wearing element must be replaceable in place without dismantling the hopper, and there must be a spare of that element on site. For a pinch valve that is the sleeve; for a butterfly valve it is the seat. Both are consumables — our valves carry a 12-month warranty on the valve body, with elastomer wear parts excluded.

Answer those and the valve type usually selects itself. Read the bulk solids valve selection guide, review bulk solids handling valves, or browse the full range. Tell us the material and the outlet and we will recommend a valve.