Understanding Rotary Valve Design

What is a Rotary Airlock Feeder?

Rotary Valves are often referred to by various names (Airlocks, Feeders, Star Valves, etc.).  Depending on the application, its function often dictates what it is called. (See blog article “What is a rotary valve?”)

Let’s take a look at definitions of “rotary” and “valve” from Webster’s:

Rotary -Having an important part that turns on an axis

Valve - Mechanical devices by which the flow of liquid, gas, or loose material in bulk may be started, stopped, or regulated by a movable part that opens, shuts, or partially obstructs one or more ports or passageways

In industry, a rotary valve is used to regulate the flow of a product, usually to reduce the flow rate to a level more suitable to the process being undertaken. Often, applications do so between areas where gas pressures are different on the different sides of the valve.

• Function as a Feeder:

Meters material into or out of something based on an assumed volume.

• Function as an Airlock:

Serves as a seal between a hopper, bin, conveying line or other area of differential pressure while still allowing material to pass through it.

Basis of Design:

Housing & End-plates

Rotary valves are made up of 4 main parts; cylinder (or housing), end-plates, rotor, and drive package. Magnum Systems’ rotary valves are made from cast gray iron, stainless steel and or Hard Chrome. The reason the housings are made out of a cast mold is the strength it adds to the design that is not possible if just fabricated.  Rotary valves are  often installed into very harsh environments and need to withstand abrasive products.

The Rotor

The internal rotor serves as the metering device on the airlock. Rotors, both open and closed end, are constructed by welding 3/8” thick vanes onto a pre-machined shaft. The closed end rotor then has a shroud welded on each end of the assembly. Rotor shafts have large diameters to minimize material deflection under load. The use of steel rather than cast iron for the rotors prevents vanes from breaking off when a foreign object becomes lodged between the rotor and housing.

Rotors can be coated to help product flow.  Types of coatings include: Hard Chrome, Teflon, Stellite, Nedox®, and Tungsten Carbide all applied based on the material the valve is handling, its flow properties, and level of abrasiveness. For more information on rotor options read this blog: “What you need to know about Rotors in Your Airlock”

Bearings, Seals and Drive Package

Outboard bearings: The outboard bearings allow smooth rotation of the rotor with minimal deflection. The bearings are outboard to the end plate. They are kept clean and free from foreign matter by factory deign. They are not exposed to product or heat with this design and are factory lubricated for the life of bearing.

Seals and Rope Packing: U-Cup seals and or rope packing are used to create an air tight seal around the shaft of the rotor. This prevents material from escaping around the shaft while it rotates.  The application the rotary valve is used in determines the seal (or packing) needed. Moly Impregnated Urethane U-Cups seals are used in applications up to 230° F, Teflon impregnated high temperature rope packing is used in applications up to 500° F, and FDA approved rope packing is used in  both standard and high temperature applications for food.

Chain and Drive Assembly: A rotary valve drive package consists of a motor, gearbox, chain, sprockets and a guard. The drive package provides constant power to the rotor.  They are sized to match torque and overhung load requirements for each size rotary valve. Rotor speeds are controlled primarily by sprocket size to maximize range of rotor RPM.  Variable speed drives are also available to more easily change speeds when needed.

Final Remarks

The rotary valve, at its core, is a simple device. Its impact on a material handling system can be huge to a facilities output when processing dry bulk solids. When functioning as an airlock, the need for tight clearances to be maintained and resist widening due to wear is paramount.  Our rotary valve designs are built to withstand the harshest environments. Whether you are purchasing a pneumatic conveying system or just a standalone replacement rotary valve you want to know it will last.  Magnum Systems’ provides valves that can let you rest easy knowing your valve is built to do so.