ROTARY VALVES AND VENTURI SYSTEMS - ROLES IN PNEUMATIC CONVEYING

Rotary valves and venturi systems are commonly used in pneumatic conveying systems. They play different roles though, and there are two major differences in how they are applied.

Understanding the role of rotary valves and venturi systems in pneumatic conveying

How do rotary valves work?

A rotary valve is a compact mechanical device using gravity flow for continuous transfer of bulk powders or granules. It is considered a simple machine because it has only one moving part. This is a multi-vane rotor that revolves in close contact with the rotary valve housing. The other non-moving parts include an inlet on top and an outlet at the bottom. Read more about the rotary valve.

Parts and operation of rotary valves

When are rotary valves used in industry?

A rotary valve is used for the following functions:

• Control and maintain a given product flow rate
• Maintain gas pressure differential between the inlet and outlet
• Act as an explosion barrier, flame barrier and process isolator

The industries that use rotary valves include:

• Agriculture, pharmaceuticals and pet food
• Biomass, power generation and waste to energy
• Coal, minerals and chemical, aggregates, asphalt and cement
• Food, grain, dairy, baking and milling
• Paper, paint, plastics and powder coating
• Steel mills, foundries, rubber, textile, tobacco and wood

Rotary valves have several major industrial applications.

Emptying of silos

Rotary valves are placed under silos, hoppers or other container systems. They are used to control bulk solid discharge from these units and to feed devices like heliflows, flexible screw conveying, pneumatic conveyors and mixers.

Discharging of cyclones

Rotary valves can also be placed under a cyclone. This applies a pressure seal between the storage and conveying systems so material flows uniformly from the outlet.

Dust collecting process

Dust collection systems utilise rotary valves to unload dust. They are used to transition material from one pressurised point, such as a dust collector, to an unpressurised point, such as a drum or bin. The valve seals a pressurised system against loss of air volume and air pressure. This allows dust from hoppers, bins or silos to be captured and returned to the material processing or conveying system.

Mixing and batching process

Rotary valves control the rotor speed of the airlock, which allows volumetric measurement of both powdered and granular bulk materials.

Feeding pneumatic conveying systems

Rotary valves are also used to feed pneumatic conveying lines from hopper, silo, cyclone and big bag discharge stations. This aids in preventing air leakage from the conveying line while maintaining constant feeding of powders or granules.

Air locking pneumatic conveyors

Rotary valves also aid pneumatic conveyors feeding from silos, hoppers and screw feeders by sending bulk materials into airlocks before being moved into another device. This enables their use as an airlock for pneumatic conveyors.

Read up more on the rotary valves we can supply rotary valve.

How do venturi systems work ?

A venturi system is a section of pipe with a cone-shaped constriction that transports materials, such as continuous edge trim, offcuts, roll ends, blow and injection moulded products and waste. With no moving parts, it is considered the simplest of machines.

Unlike rotary valves that rely on the properties of gravity flow, venturi systems rely on the properties of fluid flow. The mechanics explaining how a venturi system works are based on the conservation of energy in fluid flows, as given by the Bernoulli equation.

A venturi system has the following features:

• Converging conical inlet
• Cylindrical throat
• Diverging recovery cone

Venturi system in action showing airspeed and air pressure changes

See how Bernoulli principle explains how air entering a constriction in a tube will increase its speed but decrease its pressure

Bernoulli equation

Unlike rotary valves that rely on the properties of gravity flow, venturi systems rely on the properties of fluid flow. The mechanics explaining how a venturi system works are based on the conservation of energy in fluid flows, as given by the Bernoulli equation.

The Bernoulli equation states that the sum of all forms of energy in a fluid (including gases) flowing along an enclosed path is the same at any two points in that path. That is, energy within the fluid is conserved. As a consequence, fluid passing smoothly through a pipe with constrictions will be subject to various changes in speed and pressure in order to maintain energy conservation.

Bernoulli equation as applied to venturi systems

See how the Bernoulli equation is used to describe the movement of a fluid through a pressure difference. You can also watch on youtube too.

When is a venturi system used in industry?

A venturi system is typically used to transport suitable materials through a pipe using an air vacuum effect. It is used in transporting materials such as:

• Continuous paper edge trims
• Film and expanded polystyrene off cuts
• Guillotine off cuts and roll ends
• Blow moulded bottles and injection moulded products
• Blow and injection mould waste such as tops, tails and sprues

The industries that use venturi system include:

• • Paper and plastic manufacturers
  • Blow and inject mould factories
  • Printers, packaging, waste and recycling plants
  • Petrochemical and liquid chemical storage facilities

Transport of materials

Transport of low density granules (EPS and EPP), blow moulded items, continuous cut trim in medium speed productions and shredded material from small shredders using suction. The controlled airspeed is used to minimise the impact on the conveyed items.

Separation process

Different types of material being transported in an air flow can be separated through pipe diverters and changes in air pressure. This includes situations like removing flash and rejects from blow moulding machines.

Exhausting process

A venturi system is used in applications that require the removal of gases on a continuous basis while maintaining pressure at a stable pressure level. Examples of this include removing smoke from machining or welding areas.

Evacuation process

Venturi systems with jet pumps can be used for the evacuation of gases from tanks or vessels. Gas is steadily pulled from the tank or vessel until a desired lower pressure is achieved. The lowering of pressure in the tank or vessel can be used to purge detrimental gases.

Kongskilde inline venturi system

Kongskilde has unrivalled expertise in the handling of process waste produced in various industries. This includes their various inline venturi systems.

Why choose the Kongskilde inline venturi system?

Despite there being many manufacturers of venturi systems, Kongskilde leads the competition. Its use of high quality materials, precision construction and having no moving parts means there is almost zero maintenance.

It has the following features:

• Improved suction allows materials to enter directly into pipes
• Allowing materials to pass freely through the venturi makes for efficient conveying
• Suitable for low density, continuous lengths and odd-shaped materials
• Connects seamlessly with Kongskilde blowers and pipes

We supply Kongskilde inline venturi systems

Rotary valves and venturi systems: what to use?

We now come to the big question: what system should I use for my pneumatic conveying system?

When the pneumatically conveyed materials are low density, continuous lengths and odd shapes made of paper or plastics that need to be transported, a venturi system is needed. Such materials include continuous edge trim, offcuts, roll ends, blow moulded and injection moulded products and waste.

When, however, materials to be pneumatically conveyed are bulk powders and granules that need to discharge in a continuous and controlled fashion, then rotary valves are required.

Need advice on rotary valves and venturi systems

Do you need help figuring out the best system to use for your factory and plant? We are happy to help you. Feel free to send us a message from the Pneuvay website contact page or our Facebook page.