Glossary
What do these rotary valve terms and material processing concepts mean?
Bulk material processing can be complicated — we know firsthand! Here are some common terms and definitions related to rotary valves, parts, NFPA compliance, material characteristics, and more.
A
Abrasiveness
Abrasiveness indicates how rough, coarse, or gritty your material is, which impacts how quickly it wears down your conveying equipment. More abrasive materials require coatings and options to protect your rotary valve.
Attrition or Friability
If your material is friable, its particles are less durable, meaning it’s easier to break down the material into smaller pieces. Valve options are available to help break down chunky material into pieces that are easier to convey.
B
Bearings
As the rotor moves material from one end of the valve to the other, bearings provide mechanical support. We recommend outboard bearings, which are placed outside the housing to prevent material buildup and possible contamination.
C
Coefficient of sliding friction
How much friction and adhesion occurs between a surface (your equipment) and a particle (your material)? That’s the coefficient of sliding friction. We use it to predict whether bulk materials tend to plug, abrade, or build up.
Cohesion
Like stickiness, cohesion measures how likely particles are to stick or cake together. If material is too cohesive, it could cause arching and ratholing in bins, silos, and hoppers. We have flow aids and coatings to help prevent material sticking.
Compressibility
How does your material react to changing pressure conditions? We call that compressibility. Options like the housing vent port help to prevent air or material blowback in the case of compressible materials.
Combustible Dust
According to the NFPA, combustible dust is a fine, solid particle that may present a flash fire or explosion hazard under one of two conditions: when the particle is suspended in air, or when it comes into contact with specific concentrations of oxidizing media.
Basically, if you combine it with an oxidizer and an ignition source, combustible dust can cause a deflagration or explosion in your plant.
Not sure if your material is classified as a combustible dust? There are independent labs that can assess this for you.
D
DHA
To understand the risk of fire and explosion created by combustible dusts in your plant, you should perform a Dust Hazard Analysis (DHA) regularly. The DHA helps you identify opportunities to manage risks and make your facility safer.
If your facility handles, generates, or stores combustible dusts, NFPA 652 requires you to perform a DHA every 5 years.
Deflagration
Deflagration fires spread quickly through a facility, moving down the conveying line as other hot materials ignite. They are dangerous and difficult for fire crews to handle, so it’s important to have NFPA-compliant rotary valves to help slow the spread of flames.
Deflagrations can happen when a heat source moves over cold materials or combustible dusts and ignites them.
Dust Explosion
When you take the three elements required to start a fire (fuel, ignition, and oxidizer) and add two additional requirements, confinement and dispersion, a dust explosion can occur.
That means you have ignition and an oxidizer as usual, but the fuel particles are dispersed in the air, and the confined space allows pressure to build as gases expand.
Dust Collection (Dust Collector)
Dust collection systems recapture loose particles from your material handling system, helping to prevent waste and maintain air quality in the plant. Rotary valves for dust collectors must maintain a tight seal and have special features for NFPA compliance.
E
Endplate
Most rotary valves have two endplates: one covering either side of the housing to keep it sealed while running. When it’s time to power down for maintenance or cleaning, you will need to remove one of the endplates to access the housing.
Explosibility
Dust explosions can happen when combustible dust, a potential fuel source, is dispersed in a confined space with oxygen and an ignition source. NFPA compliance features and a TEXP motor can help keep your workers and facility safe when your material is explosible.
F
Flowability
Flowability is another term for material flow. In essence, it indicates how well your bulk solid material flows through your rotary valve and conveying line.
Fuel Source
There are three key ingredients required to start a fire: fuel, ignition, and an oxidizer. Fuel could be any type of particle that contributes to this process, but the NFPA also has a list of combustible dusts with characteristics that increase the risk of fire, deflagration, or explosion.
H
Housing
The rotary valve’s inner chamber is called the housing. This is where the rotor conveys material from one end of the valve to the other. Sometimes the housing is coated to improve efficiency.
Heavy Plate Chrome
Truly heavy-duty applications use heavy plate chrome to coat the rotary valve housing and endplates. Cement is a common application, as the material wears down parts quickly unless they are properly protected.
Hard Chrome
For rotary valves that need a bit more abrasion and sticking resistance, hard chrome is a solid choice. It is used as a coating to prevent material from wearing down the internal housing and rotors too quickly.
I
Ignition
There are three key ingredients required to start a fire: fuel, ignition, and an oxidizer. If the ignition source creates enough heat or movement near a fuel source that is exposed to oxygen, it can ignite a fire.
Ignition can happen when temperatures rise too high on your conveying line; when machinery moves too fast and creates enough friction to spark; or when there is too much air entering your positive-pressure conveying system.
Isolation Device
In a fire safety context, isolation devices help stop fires from spreading further. As long as it is well-maintained and NFPA compliant, a rotary airlock valve can act as an isolation device, stopping the spread of flames along your conveying line.
L
Lectrofluor
FDA and USDA compliant, Lectrofluor is a polymer-based coating for rotary valve rotors. It provides corrosion resistance and prevents sticking for lighter materials with less moisture content, such as powdered sugar.
M
Material Bulk Density (PCF)
Material bulk density is measured in pounds per cubic feet (PCF). Density is part of the equation we use to determine the ideal sizing for a rotary airlock valve.
N
NFPA
The National Fire Protection Association (NFPA) publishes more than 300 consensus codes and standards used to minimize the risk of fire and its effects, as well as any related risks. Your processing facility should follow these codes to keep workers and assets safe.
O
Oxidizer
There are three key ingredients required to start a fire: fuel, ignition, and an oxidizer (or simply oxygen). Oxygen is more likely to be a hazard when there is a leak in your system, causing a high concentration of oxygen, or when your ventilation system is not working properly.
P
Particle Size, Distribution and Shape
The size, distribution, and shape of particles in your material all contribute to material flow in various ways. Options are available to promote flowability in different types of material.
Permeability
Does gas or air flow easily through your material, or is there resistance? This is permeability in a nutshell. Depending on the permeability, you may need flow aids to keep material aerated.
Pneumatic Conveying (Pneumatic Conveyor)
Pneumatic conveying systems use pressurized air to either push material down a line (pressure conveying) or draw it towards the end point (vacuum conveying). Rotary valves for pneumatic conveying should provide consistent metering by maintaining the right pressure differential at all times.
R
Rotary Valve (airlock, valve, rotary airlock, rotary airlock valve, rotary feeder, rotary airlock feeder)
A rotary valve is a critical piece of conveying equipment in any material handling system. It serves as a link or transfer point between two areas, whether it’s between two containers (like bins, hoppers, or silos), or from a container to a conveyor.
A valve may act as a pressurized seal between each point (airlock), control the flow of material (feeder), or both (rotary airlock feeder).
These terms are sometimes used interchangeably, but “rotary valve” is the standard umbrella term.
Rotor
Often designed with 6, 8, or 10 vanes, a rotor rotates inside the valve’s housing and moves material through at the desired efficiency. Material enters the valve through the inlet, fills the rotor vanes or pockets, and leaves at the outlet. As it moves, empty vanes return to the top to be refilled.
RotorRail (Rail System)
A rail system is an alternate style of rotary valve design. For example, any valve with a Quick-Clean RotorRail allows operators to access the housing by pulling it out on a sliding rail system. This makes it faster and easier to clean or maintain, making it ideal for sanitary applications.
Rotor-to-Housing Tolerance
The rotor-to-housing tolerance, or clearance, is a measure of the distance between the rotor and the valve housing. It needs to be measured often to ensure it stays under the NFPA-compliant standard of 0.0079’’. Precise tolerances are needed to keep the valve running smoothly as an airlock, preventing potential issues like material buildup, blowby, leakage, and contamination.
If the tolerance rises above that number, the rotor should be replaced.
S
Shaft Seal
Each rotary valve endplate comes equipped with a shaft seal, which is responsible for sealing air inside the valve. It should be replaced regularly to prevent air leakage and contamination.
Stainless-Steel
Stainless-steel is commonly used in a rotary valve’s construction. Sometimes rotors or entire valves are made of stainless-steel, while other times it is used to improve sanitation and material flow for food-grade applications.
T
Tungsten
For the toughest customers, we coat rotary valves with tungsten, a type of metal known for its high melting point and heavy abrasion resistance. It’s like a suit of armor for your housing, endplates, and rotor.
V
Valve Rotation Speed (RPM)
Valve rotation speed is measured in rotations per minute (RPM). Speed is part of the equation we use to determine the ideal sizing for a rotary airlock valve.
X
XTR-Coat
Sometimes materials are both corrosive and prone to build-up, which is the perfect case for XTR-Coat. This FDA and USDA-approved coating is used to help highly corrosive materials like salt, or sticky materials like granulated sugar and flour, to flow through a rotary valve with ease.