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UNDERSTANDING THE ROLE OF ROTARY VALVES AND VENTURI SYSTEMS IN PNEUMATIC CONVEYING

 

Wednesday, February 15, 2017


Rotary valves and inline venturi systems are commonly used in pneumatic conveying systems. However, these two have major differences. Thus it is used distinguishingly in various applications.

Uses of rotary valve in industry
Uses of venturi system in industry


How does a rotary valve work?


A Rotary valve is a compact mechanical device used for continuously charging bulk powders or granules under gravity flow. It is considered the simplest of machines because it only has one moving part and a multi-vane rotor revolving in close contact in the housing. Other parts include an inlet on top and an outlet at the bottom as seen in the image below. 

Rotary valve movement and parts
Read more about Pneuvay Engineering's rotary valve


When is a rotary valve 


used in industry?


A rotary valve is used for the following functions:
  • Control product flow rate (as required)
  • Maintain a gas pressure differential between the inlet and outlet
  • Act as an explosion barrier, flame barrier and process isolator
Its specific function includes:


Emptying of silos 


Rotary valves are placed under silos, hoppers or other container systems. It is used to control bulk solid discharge from these units and feed devices like screw feeders, conveyors and mixers.


Discharging of cyclones 


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


Dust collecting process


Dust collection systems also utilises rotary valves to unload dust. It is used to transition material from one pressurised point, such as a dust collector, to another unpressurized point, such as a drum or bin. The valve seals a pressurized system against loss of air and pressure. This makes it to control the flow of material from hoppers, bins, or silos into processing or conveying systems. 


Mixing and batching process


Rotary valves control the rotor speed of airlock, which allows volumetric measurement to be possible for both powdered and granule type bulk materials. 


Pneumatic conveying systems 

with airlock requirements

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. 


Feeding and discharging of conveyors 

and screw feeders


Rotary valves also aid conveyors feeding from silos, hoppers and screw feeders by sending bulk materials into airlocks before it gets moved into another device. 

Visit our dedicated page for rotary valves to learn more about it.


What is a venturi system?


A venturi system is considered as one of the most accurate flow-sensing element, if and only if, it is accurately calibrated. Thus it is important to choose a pneumatic conveying company who has long years of experience in this field. 

It is consists of the following:
  • Converging conical inlet
  • Cylindrical throat
  • Diverging recovery cone


How does a venturi system work?


Unlike rotary valves that relies on gravity flow, Venturi systems follow the Bernoulli equation. 

The Bernoulli Equation


Under this principle, it states that the sum of all forms of energy in a fluid (including gas) flowing along an enclosed path is the same at any two points in that path. 


As a consequence of this principle, fluid passing through smoothly with varying constrictions can be subject to various changes in velocity and pressure. Just take a look at the below illustration:

Change of pressure in a venturi system

A venturi system speeds the flow of the fluid by constricting it in a cone shape tube. By doing so, it forces the system to have increased velocity application while reducing pressure. This creates a partial vacuum within it. 

Kongskilde Inline Venturi System
Kongskilde Inline Venturi System

As the fluid leaves the constriction, increased pressure is released back to the pipe level as shown in this short clip:


When is a venturi system 

used in industry?


A venturi system is typically used in processes that require a pumped force to flow through a tube as it increases and decreases the speed of the fluid within the tube. It is used for:


Exhausting process


A Venturi system is used in applications that require the removal of gases at a continuous rate while maintaining pressure at a stable level such as removing smoke from a machining or welding area. 


Evacuation process


A Venturi system pumps tank down from a starting pressure to a final lower pressure, which is a requirement often used in the evacuation process. This reduces the pressure in a reaction vessel so it can be purged of detrimental gases. 

The evacuation process requires pulling gases, with the use of jet pumps, from a defined volume by pumping the tank down from a starting pressure to a final lower pressure. It is often used to reduce the pressure in a reaction vessel to purge it of detrimental gases. 

The Kongskilde Inline 

Venturi System


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

It is used in various industries including:
  • Continuous edge trim from paper
  • Film manufacturing
  • Processing
  • Expanded polystyrene (E.P.S)
  • Guillotine off cuts
  • Roll ends
  • Blow moulded bottles
  • Injection moulded products
  • Blow/injection mould waste such as top, tails and sprues


Why choose the Kongskilde Inline Venturi System?


With many manufacturers of venturi systems, Kongskilde leads the competition due to the following reasons:
  • Improved suction allowing materials to enter directly into the pipes
  • Efficient conveying of product by allowing it to pass freely through the Venturi 
  • With no moving parts, the Inline Venturi System requires very low maintenance
  • Suitable even to low density, continuous lengths and odd shaped materials
  • Easily connects with other Kongskilde blowers and pipes 


Rotary valves or venturi system: 

what to use?


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

A pneumatic conveying system that requires suction and varying pressure applications within the pipeline is better off with a venturi system. However, for industries requiring the continuous charging of bulk powders such as the following, it may be better to use rotary valves. 

  • Agriculture and pet food
  • Aggregates, asphalt and cement
  • Dairy, baking and milling
  • Coal, minerals and chemical
  • Biomass, energy and power
  • Food, foundries and grain
  • Paper and paint
  • Plastics and powder coating
  • Pharmaceuticals
  • Steel Mills, rubber and textile
  • Tobacco and wood
  • Waste to Energy

Do you need help figuring out the best system to use for your factories and plants? We are happy to help you. Contact us online so we can schedule an appointment with you. 


 
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