What is a Positive Displacement Blowers

Positive displacement blowers are a type of air compressor that works by trapping a specific volume of air between two meshing lobes, or rotors, and then compressing and releasing that air as the rotors rotate. These blowers are used to generate high-pressure air or gas flow for a variety of applications in industries such as wastewater treatment, chemical processing, and pneumatic conveying.

positive displacement blowers

Positive displacement blowers are classified as a type of positive displacement pump, which means they move a fixed volume of fluid with each cycle. Unlike centrifugal pumps, which rely on the kinetic energy of impellers to move fluids, positive displacement pumps use mechanical means to move fluids. In the case of positive displacement blowers, the lobes rotate within a casing, trapping air between the lobes and casing, which is then compressed and discharged.

Positive displacement blowers are known for their high efficiency and reliability, making them a popular choice for applications that require consistent and reliable compressed air or gas. They are also relatively low maintenance and have a long service life, which makes them a cost-effective choice for many industrial applications.

positive displacement blowers of types

Two main types of positive displacement blowers:

  1. Roots blowers: These are also known as rotary lobe blowers, and they use two symmetrical lobes that rotate in opposite directions within a casing to compress and discharge air. Roots blowers are known for their high volumetric efficiency and can handle a wide range of air flow rates.
  2. Screw blowers: These use two intermeshing screws or rotors that rotate within a casing to compress and discharge air. Screw blowers are known for their high efficiency and low noise levels, making them a popular choice for applications that require quiet operation.

Both types of positive displacement blowers have their own advantages and disadvantages, and the choice between them depends on the specific application requirements. For example, Roots blowers are often preferred for high-pressure applications, while screw blowers are better suited for low-pressure applications that require high flow rates. Additionally, the choice between these types of blowers depends on factors such as the desired operating pressure, flow rate, and budget.

Twin Lobe vs. Tri-Lobe

typically utilize a straight lobe rotor design with two or three lobes and are characterized as twin lobe rotary air blowers and tri-lobe rotary air blowers. A twin lobe blower contains two figure 8 shaped lobes while a tri-lobe blower consists of three lobes shaped like a boat propeller.

positive displacement blowers of types

positive displacement blowers working principle

The working principle of positive displacement blowers involves the movement of air between two rotating lobes, which compresses and discharges the air.

Here are the steps involved in the working principle of positive displacement blowers:

  1. The blower consists of two rotating lobes or rotors, which are typically made of cast iron or other durable materials. These rotors are designed to mesh with each other and rotate in opposite directions within a casing.

  2. As the lobes rotate, they create a space between them that draws in air from the intake side of the blower.

  3. The air is trapped between the lobes and the casing as the rotors continue to rotate, and it is compressed as the space between the lobes decreases.

  4. When the lobes reach the discharge side of the blower, the compressed air is forced out of the blower and into the discharge line.

  5. The cycle is repeated as the lobes continue to rotate, with air being drawn in from the intake side and discharged from the discharge side.

Positive displacement blowers are typically designed to operate at a constant speed and deliver a consistent volume of air or gas, making them ideal for applications that require a steady flow of compressed air or gas. The working principle of positive displacement blowers allows them to generate high-pressure airflow without the need for complex valves or other components, making them a simple and reliable choice for many industrial applications.

applications

  1. Wastewater treatment: wastewater treatment plants to provide the compressed air needed for aeration processes. They are used to supply air to diffusers that release bubbles into the wastewater, which promotes the growth of bacteria that break down organic matter.
  2. Pneumatic conveying: They are used to transport powders, granules, and other materials through pipelines in pneumatic conveying systems. The blower provides the compressed air needed to move the material through the pipeline.
  3. Chemical processing: They are used in chemical processing plants to supply compressed air or gas for various processes, such as mixing, agitating, and drying.
  4. Food processing: They are used in the food processing industry to supply compressed air for various processes, such as conveying and packaging.
  5. Vacuum systems: They are used in vacuum systems to create suction for various applications, such as holding parts in place during machining or lifting heavy objects.
  6. Power generation: They are used in power generation to provide the compressed air needed to control turbine blades and other components.

question and answer

A positive displacement blower is a machine that uses rotating lobes, screws, or vanes to trap air or gas and move it from the inlet to the outlet. It is a type of compressor that delivers a constant volume of air or gas at a fixed pressure.

Positive displacement blowers are used in a wide range of applications, including wastewater treatment, pneumatic conveying, vacuum cleaning, food processing, and chemical processing. They are also used in the oil and gas industry for vapor recovery, gas boosting, and flare gas recovery.

A positive displacement blower works by trapping air or gas between rotating lobes, screws, or vanes and the chamber housing. As the rotor turns, the volume of air or gas trapped between the lobes or vanes is reduced, causing compression. The compressed air or gas is then discharged through the outlet.

Positive displacement blowers are efficient, reliable, and can handle a wide range of operating conditions. They are also low maintenance and have a long service life. They are ideal for applications that require a constant volume of air or gas at a fixed pressure.

The most common types of positive displacement blowers are Roots blowers, screw blowers, and vane blowers. Roots blowers use two or three interlocking lobes to trap and move air or gas. Screw blowers use two or three rotating screws to compress air or gas. Vane blowers use sliding vanes that are forced against the housing to compress air or gas.

The right positive displacement blower for an application depends on several factors, including the required flow rate, pressure, and temperature, as well as the type of gas or air being moved. Other factors to consider include the installation space available, the electrical supply available, and the level of noise or vibration that can be tolerated.

Positive displacement blowers require regular maintenance to ensure optimal performance and longevity. This includes regular oil changes, an inspection of the belts and pulleys, and checking for any leaks or unusual noises. It is also important to clean the intake filter and lubricate the bearings and gears as needed.

The main difference between a positive displacement blower and a centrifugal blower is the method of compression. Positive displacement blowers use rotating lobes, screws, or vanes to trap and compress air or gas, while centrifugal blowers use a high-speed impeller to generate a flow of air or gas. Centrifugal blowers are better suited for applications that require high pressure and low flow rates, while positive displacement blowers are better suited for applications that require low pressure and high flow rates.

Yes, positive displacement blowers can be used as vacuum pumps by reversing the direction of flow. Instead of compressing air or gas, the blower will draw in air or gas and create a vacuum.

The maximum pressure that a positive displacement blower can produce depends on the type of blower and its design. Roots blowers typically produce pressures up to 15 psi, while screw and vane blowers can produce pressures up to 30 psi.

Yes, positive displacement blowers can be used to compress a wide range of gases, including nitrogen, methane, hydrogen, and others. However, it is important to ensure that the blower is designed to handle the specific gas being compressed and that all safety precautions are taken.

The maximum flow rate that a positive displacement blower can handle depends on the type of blower, its size, and its design. Smaller blowers may have flow rates of a few cubic feet per minute, while larger blowers can handle hundreds or thousands of cubic feet per minute.

A single-stage positive displacement blower uses a single set of lobes, screws, or vanes to compress air or gas, while a two-stage blower uses two sets of lobes, screws, or vanes to provide additional compression. Two-stage blowers can produce higher pressures and greater flow rates than single-stage blowers.

A discharge silencer is used in positive displacement blower systems to reduce the noise produced during operation. It is typically located at the outlet of the blower and consists of a series of baffles or chambers that absorb sound waves.

Common problems that can occur with positive displacement blowers include leaks, wear on the lobes, vanes, or screws, damaged bearings or gears, and clogged filters. It is important to perform regular maintenance and inspections to identify and address any potential issues.

The lifespan of a positive displacement blower depends on several factors, including the type of blower, its design, the operating conditions, and the level of maintenance. With proper maintenance and care, positive displacement blowers can last for many years.

Positive displacement blowers and centrifugal blowers are both used for air and gas handling, but they operate differently. Positive displacement blowers use lobes, screws, or vanes to compress air or gas, while centrifugal blowers use a rotating impeller to impart kinetic energy to the air or gas, which is then converted to pressure. Positive displacement blowers are better suited for low-pressure, high-volume applications, while centrifugal blowers are better suited for high-pressure, low-volume applications.

The efficiency of a positive displacement blower is typically lower than that of other types of compressors, such as screw compressors or centrifugal compressors. However, positive displacement blowers are well suited for low-pressure, high-volume applications where efficiency is not the primary concern.

Yes, positive displacement blowers can be designed and certified for use in hazardous or explosive environments. They can be made from materials that are resistant to corrosion and abrasion and can be equipped with explosion-proof motors and other safety features to prevent ignition of flammable gases or dust.

While blowers and compressors are both used for compressing air or gas, they operate differently. Blowers typically provide low to moderate-pressure ratios and high flow rates, while compressors provide high-pressure ratios and lower flow rates. In addition, blowers are typically designed for continuous duty and lower speeds, while compressors may operate intermittently and at higher speeds.

When selecting a positive displacement blower for a specific application, several factors should be considered, including the required flow rate and pressure, the type of gas being compressed, the temperature and humidity of the