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Rotary valve capacity, power

Q: How does one determine the capacity of a rotary valve and the power needed by a rotary valve for a given capacity?

A: The capacity of a rotary valve is the revolutions/minutes times the effective volume of the pockets. The volume of the pockets is the volume of each pocket times the number of pockets (usually 6 or 8). The effective volume is the effective fill of these pockets and is limited by the amount of aeration, speed or any restrictions to the flow path of the solids, and the diameter of the valve (because of the angle of repose of the solids). A good estimate is between 50-67% of the actual volume at low speeds and 40-50% at high speeds.

The power is not much different with or without solids as long as the gap is properly set to avoid pinching of the solids. Cohesive solids or solids that smear may require substantially higher power, but will ultimately result in failure of the valve (wear or binding). This later condition must be avoided. Dump valves or screws may need to be used. Most manufactures provide enough power to the valve to turn the rotor with a reasonable amount of friction (usually with a gap of 1-3 mm) and a safety factor of about 5 times the rotor friction. This will allow a valve to overcome most short term restrictions. Shear pins protect the valve from excessive loads due to cohesive materials or other foreign objects.

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