Rotary valve feed rate: reliable decisions depend on stated operating conditions, material evidence and equipment limits. Rotary-valve capacity is often estimated from pocket volume, number of pockets and rotor speed. That geometric result is useful for preliminary comparison, but it is not a guaranteed material feed rate. Real pockets may be partly filled, partly emptied or occupied by aerated product with a lower bulk density than the laboratory value.
Theoretical Versus Actual Capacity
Theoretical displacement assumes that every pocket fills completely at the inlet, retains the same material density and empties completely at the outlet. Production conditions rarely meet all three assumptions.
Actual output depends on:
- Product supply and hopper geometry.
- Bulk-density and moisture range.
- Rotor pocket shape and surface condition.
- Inlet opening and shear edge.
- Rotor speed and available filling time.
- Pipeline pressure and gas leakage.
- Pocket discharge and entrainment behavior.
The ratio between actual and geometric capacity is commonly described as filling efficiency, but it is not one permanent valve constant.
Effect of Rotor Speed
Increasing speed creates more pocket cycles per minute. At first, material rate may rise approximately with speed. At higher speed, pockets have less time to fill and discharge, so output can deviate from a straight-line prediction.
Very low speed can create large intervals between solids pulses, especially in a small conveying line. These pulses may cause fluctuating pressure or uneven receiver load. The usable control range should therefore be demonstrated with the actual material.
Bulk Density and Material Condition
The same pocket volume carries different mass when the product is aerated, consolidated or wet. Leakage gas entering the hopper can fluidize material and lower apparent bulk density. Long storage may increase density but reduce flowability.
Feed-rate calculations should use a measured production range, not a single catalogue density. Where mass accuracy matters, a downstream weigh system can trim the feeder speed or verify batch delivery.
Hopper Level and Inlet Flow
High material head can improve pocket filling for some free-flowing products, while low hopper level can starve the valve. Cohesive powder may bridge regardless of level. Flow aids must be selected carefully because excessive aeration can increase gas displacement and reduce mass per pocket.
The inlet should allow material to enter without excessive shearing or dead zones. Large granules require clearance and geometry that prevent jamming as rotor blades pass the edge.
Pipeline Pressure and Pocket Emptying
Pressure-driven gas moves toward the hopper through clearances and pockets. If this leakage is not vented, it can resist incoming material. At the outlet, cohesive product may remain in a pocket unless gravity, geometry or a suitable blow-through arrangement releases it.
The feeder test should therefore reproduce the expected pipeline pressure, not only run the valve into an open container.
Commissioning the Material Rate
A practical test records mass delivered over a defined period at several rotor speeds, hopper levels and line pressures. The test material should represent the production particle-size, moisture and bulk-density range. Product degradation and valve temperature should also be checked.
The resulting calibration curve belongs to that material, valve and operating condition. After wear or a major product change, the relationship should be verified again.
Glossary
Calibration curve: Measured relationship between feeder setting and actual material output under stated conditions.
Filling efficiency: Fraction of theoretical feeder pocket capacity occupied and successfully discharged as useful material.
Hopper head: Material depth or load acting above a feeder inlet.
Mass throughput: Mass of material transferred per unit time.
Pocket filling: Entry and retention of bulk material within a rotor cavity before discharge.
Solids pulse: Short-duration concentration of material entering the line as a feeder pocket empties.
Starved feeding: Condition in which insufficient material reaches the feeder inlet to fill available capacity.