Rotary valves/airlocks (rotary valves) are devices with close-fitting, revolving blades/vanes installed inside industrial equipment to control the flow of materials through a process (see Figure 1). Rotary valves are used in many industries and functions. A common example (Figure 2) is an airlock used in a pneumatic conveying system to dispense material while maintaining system pressurization. The moving blades present a significant amputation hazard hidden within the housing around the rotary valves. Often, openings at the inlet and exit of the valve housing are wide enough for workers’ hands to enter (e.g. while cleaning, troubleshooting, or maintaining), allowing contact with moving blades and resulting in amputations.
From 2015 to 2020, there were 117 amputation and laceration injuries involving rotary valves nationwide. To prevent these injuries, it is important for employers and workers to understand rotary valves’ functions, hazards, and safe use. This Safety and Health Information Bulletin (SHIB) highlights five amputation cases from a single OSHA Area Office involving rotary valves and methods to prevent worker exposure to rotary valve hazards.
Rotary valves are commonly found in industries such as agriculture, food processing, aggregate processing, construction, foundries and steel mills, pharmaceutical plants, textiles, plastics, wood, and recycling. They are configured with close-fitting blades or vanes fixed to a rotating axle, inside a valve housing to control material flow. During operation, material enters the valve through an inlet and falls into the space between vanes. As the axel rotates, the material is conveyed and discharged to the next portion of the process. The two most common rotary valve functions are metering and airlock:
- Metering rotary valves transfer materials at precise flow rates or measurements. These are commonly used to ensure proper process speed or material quantities
- Airlock rotary valves move materials between two spaces with different pressures (e.g., from a gravity-fed system to a pneumatic system). The blades form a constant seal between the inlet (see top in Figure 2) and the outlet to prevent air loss and continuously move material with constant air pressure.
Rotary Valve Hazards and Case Patterns
Amputations and lacerations are the most common injuries associated with rotary valves and occur when workers physically contact the moving vanes. In many cases, workers are unaware of the moving vanes because the vanes are inside of the machine housing, not readily visible, or not labeled. Many rotary valve accidents have similar causes. During one year, an OSHA Area Office investigated the following five rotary valve accidents:
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