A blower is an equipment that works on principles similar to a fan in that it uses the displacement of air in a stream to perform some rotation.
In the manufacturing industries, industrial blowers are used. Industrial blowers are generally considered more versatile than traditional blowers because they can be used for various applications. The basic working of all industrial blowers is that they increase airflow by drawing in fresh air from outdoors. They accomplish this by passing a fan blade through a rotor, which opens and closes a set of blades. The blades, then, increase the air pressure as they pass through the air.
There are many types of industrial blowers in the market today, such as Northwest Flow Technologies PD blowers. This article will focus on discussing positive displacement blowers. You’ll learn what they are and how they work. Further down, the article will also provide some useful tips on choosing the most appropriate positive displacement blower for your needs.
What Is A Pneumatic Conveying System?
Before you can understand the function of a positive displacement blower, you need to learn more about how a pneumatic conveying system works. Pneumatic conveying systems are mechanical systems that enable the transfer of fluids in a sealed system through a fluid medium. It uses high-pressure or high-frequency vibrations to convey the fluid mass to a specific stream of compressed gas, and, then, employs air or pressure to mix the mass with the air stream.
A pneumatic conveying system provides a cost-effective way to handle or transfer bulk granular or fluid-like materials easily, with very minimal loss. It’s used in a wide range of industries, like food, cement, and chemical manufacturing industries.
For a pneumatic conveying system to work, it would require differential pressure to cause air movement. It also requires kinetic energy to help the gas push the solids, along with the pipe systems. It also requires air mass at velocity to overcome the frictional forces present in the piping system. That’s why a pneumatic conveying system needs a positive displacement blower to satisfy these requirements.
Positive Displacement Blower: How Does It Work?
To understand how a positive displacement blower works, you need to learn about its anatomy:
- Inlet Tube: This is where the air is introduced in the blower.
- Lobes: These are figure-eight gear that serves as the rotating parts of the blower.
- Discharge Tube: This is where pressurized air from the blower goes out.
- Motor: It’s responsible for the rotating power of the lobes.
When you open the blower, you’ll see these main parts. Some blowers may also have other features, like sound absorbers, air screens, and others that can help improve their efficiency. Once the blower starts, the motor will power up the lobes that’ll rotate.
As the lobes revolve, the air is pulled into the inlet tube of the blower. Then, the air is confined between the lobes and the blower casing. The revolving movement of the lobes helps create compression or increases the pressure of the air, as well as helps create air pockets. The air pocket is, then, moved around the lobes and blower casing, moving it to the outlet or discharge side. Once the rotors open to the discharge side, the line equalizes the pressure of the air, and it’s forced out of the blower.
In simple terms, the blower traps and releases the air through the discharge side. Due to the small clearance between the lobes, there’s no chance that air will cause backflow into the system. This will help the blower overcome any resisting pressure—that’s why it’s called positive displacement.
What Are The Types Of Positive Displacement Blowers?
There are two general types of positive displacement blowers. These are:
1. Roots Or Lobe-Style Blower
A root or lobe-style positive displacement blower generates a constant air volume by the displacement of rotating two or three lobes. The lobes are mounted on a parallel shaft within the casing, and they rotate in opposite directions. When the lobes open up to the discharge port, it allows some air to flow back into the casing, thus, creating pressure pulsations.
2. Rotary Screw Blower
A rotary screw positive displacement blower has a pair of rotors inside. The rotating motion decreases the available volume between them, and this causes the air to compress. As the air is continually compressed between the rotors, it’s pushed through the discharged outlet. Instead of pushing the air through pulsation, rotary screw blowers push the air directly to the discharge, making it more efficient for a wide variety of applications, including water treatment.
What Are The Advantages Of Using Positive Displacement Blowers?
The design of a positive displacement blower is straightforward, but it’s very effective in conveying materials in an industrial plant. It’s often overlooked that positive displacement blowers have many beneficial properties and are very popular with industrial users. Some of the advantages are:
Cost-Effective
Compared to other popular types of blowers, like centrifugal fans or blowers, positive displacement blowers are generally cheaper. They’re also cost-effective in terms of maintenance because they take little upkeep. When it comes to repairing, positive displacement blowers require only basic tools and general mechanical works. You won’t have to ask for highly trained technicians to check the system, unlike other types of blowers.
More Robust
Another advantage of positive displacement blowers is that they’re more robust and less sensitive. Compared to centrifugal blowers, they don’t need to be cleaned at all times because there’s less chance of dust and other particles going inside the system that can disrupt their efficiency.
Flexible
Compared to their centrifugal counterparts, positive displacement blowers offer more flexibility. Centrifugal blowers can’t tolerate liquid or gas in the stream. Positive displacement blowers, on the other hand, can be configured for liquid injection. By doing this, you can increase the overall performance and efficiency of the system.
Safer And More Efficient
Pressure and volume flow are independent variables used by positive displacement blowers while working at a constant speed. When the pressure increases, the flow rate of the air inside is unaffected. Translating this to an efficiency curve, the specific energy ratio of the machine is close to linear. This means that the efficiency of the equipment is the same across the operating range, whether the pressure is high or low.
Aside from that, positive displacement blowers will provide warnings before complete failure. A centrifugal blower, on the other hand, will depend on instrumentation. When instrumentation fails, the equipment is more likely to be beyond repair, and replacement of the unit is your only option.
How Do You Choose The Appropriate Blower For Your Needs?
The first step you should take when choosing a blower is determining the right size for your needs. When evaluating your needs, you should choose based on the following criteria:
- Throughput Rate
- Pressure
- Pumping Speed
- Vacuum
Positive displacement blowers are more effective when used for high volumes, low pressure, and vacuum applications. General measurements for choosing a blower are:
- Outlet displacement volume in cubic feet per minute
- Inlet cubic feet per minute volume of the gas entering the blower during a given period
- Throughput rate based on the product of the pumping speed and the inlet gas pressure
When you get the most appropriate size of the blower, you’ll get the greatest return on investment and cut losses.
Once you’ve determined the right size for your needs, there are other considerations you should make. First, you need to see if the blower will fit the requirements for your applications. The blower should depend on the type of gas and the conditions of the materials you’re trying to convey. It should also fit your equipment alignment, whether it’s horizontal or vertical.
Second, you should look at the blower’s energy efficiency. Choosing the right blower will maximize its productivity while using less power. An undersized blower that runs more than its capacity can cost more because it consumes more power. An idle blower that runs at 90% capacity can also cause you to spend too much on power.
Because robotics and artificial intelligence are already widely used in many manufacturing industries, many use automation when controlling the blower to ensure that it runs efficiently. Some of the industries run their blower at varying speeds to optimize their operation.
Lastly, you might want to consider noise reduction features when choosing the best positive displacement blower for your needs. This is an important factor, especially if the blower will be installed in an outside location. To protect the people working around the area and reduce noise pollution, you can choose blowers with noise-reduction features, like a one-piece cylinder or tri-lobe designs. Some blower packages contain custom silencers.
Summary
Many conveying systems in industrial plans require positive displacement of materials for them to move materials from one place to another. Positive displacement means that the system moves air in one direction and doesn’t change direction. This can be achieved by using positive displacement blowers.
The benefits of the positive displacement blowers include increased efficiency and lower maintenance costs. Both of these factors translate into more money saved over time. Since the units consume so little energy to operate, spending money on more power becomes unnecessary.
When choosing the most appropriate blower for your needs, you should always consider the size. The size of the blower will dictate if it’ll be efficient and provide you with the maximum return on investment.
