Rotary Valve Capacity Calculation Example

Rotary valve capacity is usually estimated from rotor pocket volume, rotor speed, filling efficiency and material bulk density. The final selection should also consider material flow behavior, pressure difference, leakage, temperature and installation conditions.

This page gives a simple explanation for buyers who want to understand the basic calculation logic before requesting model selection support.

Basic capacity factors

• Rotor pocket volume

• Rotor speed

• Filling efficiency

• Material bulk density

• Leakage and pressure condition

• Material flow behavior

Simple calculation logic

Theoretical volume capacity is related to pocket volume and rotation speed. Actual capacity is usually lower than theoretical capacity because the pockets may not fill completely, especially when the material has poor flowability.

For weight capacity, the volume capacity is combined with bulk density.

Worked example with assumed values

This is an illustrative calculation, not a FUWEI model rating, test result or performance guarantee. Assume a total rotor displacement of 10 litres per revolution, a rotor speed of 20 revolutions per minute, a filling fraction of 0.60 and a loose bulk density of 500 kg/m3. The displacement is the total for one complete rotor revolution, not the volume of a single pocket.

1. Convert displacement: 10 litres per revolution = 0.010 m3 per revolution.

2. Theoretical volume rate at full filling: 0.010 x 20 x 60 = 12 m3/h.

3. Estimated volume rate at the assumed filling fraction: 12 x 0.60 = 7.2 m3/h.

4. Estimated mass rate: 7.2 x 500 = 3,600 kg/h, or 3.6 tonnes per hour.

In this simplified estimate, volume rate (m3/h) = total displacement (m3/revolution) x speed (revolutions/minute) x 60 x filling fraction. Mass rate (kg/h) = volume rate (m3/h) x bulk density (kg/m3).

What changes if filling is lower?

Keeping the other assumed values unchanged, a filling fraction of 0.40 gives 4.8 m3/h and 2,400 kg/h. Neither 0.40 nor 0.60 is a recommended default. Filling depends on the material and operating conditions; increasing speed does not guarantee a proportional increase in output.

Use the valve's documented displacement and material-specific operating data for selection. Do not use solid particle density in place of loose bulk density. This estimate does not calculate air leakage, drive power, allowable pressure or safe operating limits.

Send your material, bulk density, required throughput, temperature and pressure difference to FUWEI for selection support.

Why filling efficiency matters

Fine powder, sticky material, irregular particles and poor inlet feeding can reduce filling efficiency. This is why two materials with the same bulk density may still need different selection recommendations.

Why capacity calculation is only one part of selection

Capacity calculation helps narrow the size range, but it does not replace full selection. A rotary airlock valve used under pressure difference must also consider sealing performance, air leakage, rotor clearance, wear resistance and drive configuration.

Information to send for support

• Material name

• Bulk density

• Required capacity

• Particle size

• Temperature

• Pressure difference

• Inlet and outlet size

• Application: silo discharge, batching, pneumatic conveying or other use

Related guides

rotary valve capacity calculation guide | rotary airlock valve sizing guide | rotary valve selection parameters | rotary airlock valve products