Valve and Airlock Selection for Pet Food Plants

The difficult material in a pet food plant is not the meal; it is the finished kibble after coating. Fat and palatant make it adhesive, and every sliding surface, seal face and pocket collects a layer. The layer builds until a gate blade no longer seats, and the symptom is not a mechanical alarm but recipe carryover.

Carryover matters here more than people outside the industry expect. A poultry free diet, a prescription product or a single protein line has claims on the bag, and the valve that leaked between recipes is where those claims fail.

At the same time the product is fragile. Extruded kibble breaks under shear, and broken kibble is screened out as fines. A rotary valve with a tight clearance turns a percentage of good product into a by product, and on a line running tonnes an hour that percentage is money.

Meal handling upstream brings its own version of the problem: fine, fibrous and often containing fat already, so the same build up appears in the dosing valves at the mixer.

Valves that stay closed when the product is fatty, with sealing surfaces that wipe rather than collect, and with inspection points that make the state of the seal visible without dismantling.

Gentle handling of finished product, with gates preferred to rotating clearances wherever no air boundary is required.

Cleaning that fits the number of changeovers the plant actually runs, which is usually more than the specification assumed.

For pharmaceutical powder handling the deciding document is measured containment data for that valve size, and a valve chosen on cleanability alone will not produce it.

The duties are separated first. In the meal and premix area the valve is a dosing or shut off device under a bin; after the coater it is a transfer device handling finished product; under filters it is a dust discharge. Those three want different hardware, and plants that buy one type for all of them get build up in the first, breakage in the second and over specification in the third.

For finished product the preference is to avoid shear entirely. Slide gates, chutes and drag conveyors move kibble without a rotating clearance, and a rotary valve is used only where a genuine pressure boundary exists. Where one is needed, a large slow valve with bevelled tips passes kibble with far less damage than a correctly sized small one.

Build up is addressed with geometry and access. A blade that wipes its seat on every stroke keeps itself clean; a seal that can be inspected through a hatch gets inspected. Both are cheaper than discovering carryover in a finished goods test.

Changeover is then counted honestly. A line running six recipes a shift needs quick release end plates and tool free seal removal, because anything slower will be skipped.

• Duties separated: meal dosing, finished product transfer and filter discharge.
• Rotating clearances avoided in finished product unless a pressure boundary requires one.
• Large slow valves with bevelled tips where an airlock is unavoidable.
• Sealing surfaces designed to wipe, with inspection access to see their condition.
• Cleaning concept matched to the real number of changeovers per shift.
• Recipe carryover treated as a product claim risk, with the valve named in the changeover procedure.

• Fat and palatant content of the stream, which decides the sealing geometry and the inspection interval.
• Kibble fragility, measured on the actual product, since breakage goes straight to the fines screen.
• Changeover count per shift and the time allowed for each.
• Claim sensitivity of the recipes sharing the line, including single protein and prescription diets.
• Pressure duty, which is the only justification for a rotating clearance in finished product.
• Cleaning method, dry or wet, and whether the valve survives it.