Category Archive: News

The Importance of Differential Pressure in Cleanrooms


At Liberty Industries, we serve as a one-stop source for all cleanroom needs. For over six decades, we have supplied superior cleanroom and contamination control supplies to customers across the globe. Equipped with extensive industry experience, our team has the knowledge and skills to design and develop a standard or custom cleanroom solution suitable for any critical environment.

In the following article, we provide an overview of one of the key operating principles of cleanrooms—differential pressure. We outline what it is, how we measure it, and how it affects other conditions in a cleanroom.

Differential Pressure in Cleanrooms

Differential pressure refers to the difference in air pressure from one location to another within a system. In cleanrooms, maintaining the right amount of differential pressure—either positive or negative—is essential to preventing contamination.

  • In positive differential pressure cleanrooms, the internal pressure is greater than the external pressure to prevent the ingress of any contaminants through any opening—whether intended or accidental—in the cleanroom.
  • In negative differential pressure cleanrooms, the external pressure is greater than the internal pressure to prevent the egress of any potentially harmful compounds contained within the cleanroom.

Combined with appropriate temperature, humidity, and airflow level, proper differential pressure levels ensure both cleanroom designs work as intended. As such, it is essential to carefully measure and monitor pressure inside and outside of the cleanroom to confirm the differential remains within the acceptable range.

Industry professionals often employ visual gauges or meters to facilitate the identification of current pressure levels inside and outside of cleanrooms. The devices are designed to automatically calculate and output the difference between two pressure points in the cleanroom (typically two inlet points), eliminating the need for operators to manually monitor separate gauges and calculate the difference between the results. More advanced measuring instruments may offer additional capabilities for monitoring temperature, humidity, and other cleanroom parameters.

At Liberty Industries, we offer Magnehelic gauges for these applications. They provide accurate measurement of pressure, pressure differential, and vacuum to 2% of full scale. In addition to cleanrooms, typical use cases include automatic valves, control equipment, and gas-air ratio controls.

Cleanroom Standards

The level of cleanliness required from a cleanroom depends on the industry and industrial application. For this reason, cleanrooms are available in numerous classifications, each of which denotes a specific level attainable based on the number and size of contaminants with the given space.

The International Organization for Standardization (ISO) categorizes cleanrooms from ISO 1 to ISO 9, with ISO 1 having the fewest contaminants per square meter. In addition to the number of particulates, the size of particulates also plays a crucial role in ISO classification. Contaminants are measured in microns, from 1μm to 5μm, with different cleanrooms offering different filtration capacities for each size. For example, cleanrooms with HEPA filters remove particulates as small as 0.3μm with 99.99% efficiency rates, while cleanrooms with ultra-low particulate filters remove particulates as small as 0.12μm with an efficiency rate of 99.999%.

The effectiveness of the mechanisms that facilitate cleanroom operations—including the filters—depend on many factors remaining within tolerable levels. These factors include pressure, temperature, humidity, and airflow, all of which can help or hinder the attainment and maintenance of proper cleanliness levels.

Quality Cleanroom Solutions From Liberty Industries

Cleanrooms play a critical role in many sensitive industries and industrial applications. For these instruments to work correctly, maintaining proper differential pressures (among other factors) is essential. To learn more about cleanrooms and the role differential pressure plays in their operation, contact us today. For assistance selecting and sourcing a cleanroom solution for your facility, request a quote.

5 Facts You Should Know About Cleanroom Filtration


Since 1953, Liberty Industries has been creating high quality cleanrooms, cleanroom filtration systems, and contamination control supplies. We have more than 65 years of experience designing and building customized cleanrooms for use in a diverse range of industries by customers around the world.

The filtration system is a critical component of any cleanroom. Well-designed cleanrooms require air filters that control air flow, remove particles from the room, and keep external pollutants out to prevent contamination of manufacturing processes, critical research or other projects.

The Facts About Cleanroom Filtration

Understanding the basics about cleanroom filtration can help to avoid contamination and ensure that the cleanroom is functioning at an optimal level. Here are five important facts:

1. There are three types of air filters.

  • Pre-filters. These filters pre-remove larger particles from the air before the it reaches more comprehensive HEPA or ULPA filters, extending the lifespan of the more expensive filters.
  • HEPA filters. High-Efficiency Particulate Air (HEPA) filters are the most commonly used filter, with capabilities to filter particles of 0.3µm or larger. Depending on the application, HEPA filters can last more than seven years before replacement is required in many applications. Based on specific cleanroom protocol, filters may have to be changed more often.
  • ULPA filters. Ultra Low Particulate Air (ULPA) filters are similar to HEPA filters, though they are capable of removing 99.999% of contaminants larger than 0.12µm. This capability to remove smaller particles makes ULPA filters the most expensive filter type.

2. Particles may be filtered in numerous ways due to a filter’s design

Depending on the design of the filter, there are four different ways particles may be filtered.

  • Straining/sieving. This filtering method catches any particles that are larger than the clearance between the fibers of the filter.
  • Inertial/impaction. The inertia of the particles forces them out of the airstream, where they get stuck to adhesive fibers.
  • Interception. Smaller particles get caught in the airstream and are carried towards the filter fiber, which then intercepts them before they can be released back into the air.
  • Diffusion. Perfect for very small particles, diffusion bombards contaminant particles with air molecules until they go into vibration mode. This vibration makes it much easier for filter fibers to catch even the smallest particles, although it has little impact on larger ones.

3. HEPA filters are the most commonly employed filter in cleanrooms.

HEPA filters were first invented in 1941 to protect scientists from Alpha particles created as they developed the atomic bomb. They are made from pleated layers of media paper, in which particles then get trapped. Filters must remove a minimum of 99.97% of particles before they can be designated as HEPA.

4. Filter maintenance should be performed regularly depending on the filter.

Since filters for cleanrooms can be used 24/7, they may deteriorate faster than other types of equipment. On average, pre-filters should be replaced six times a year and HEPA filters should be replaced every three years. However, factors such as cleanroom location, nearby construction, and air pollution can impact these maintenance schedules.

5. People are the biggest risk to proper cleanroom filtration.

While filters keep air filtered, humans pose the biggest risk to cleanroom filtration. It is the responsibility of the employee to reduce the risk of contamination and ensure that the air is being properly filtered. Proper clothing such as gowns, coveralls, gloves, face masks, and goggles can help prevent contamination from employees. Cleanrooms may also incorporate sinks, showers, and other disinfection equipment in entry and/or exit areas for applications with very high cleanliness standards.

Filtration Products Available at Liberty Industries

We offer a wide range of quality filtration products to suit every need. Some of our most popular products include:

  • HEPA/ULPA filters. Our filters are engineered to meet ISO 14644-1.
  • Pre-filters. These non-woven, fine-fibered media pre-filters allow you to upgrade preexisting systems easily.
  • Charcoal filters. Charcoal filters used primarily for odor reduction.

Work With Liberty Industries

Implementing a high-quality filtration system is vital to the functionality of any cleanroom. To learn more about how our experts can help you design or optimize your cleanroom, contact us or request a quote today.


Positive Air Pressure Cleanrooms vs. Negative Air Pressure Cleanrooms


As a manufacturer and distributor of top-of-the-line cleanrooms and contamination control products, Liberty Industries, Inc. serves as a one-stop shop for all cleanroom needs. Our expert team assists in every aspect of cleanroom creation—from design to construction and assembly—to provide custom-tailored solutions to a wide range of industries. Whether a customer requires a standard or highly specialized area; a positive air pressure cleanroom or negative air pressure cleanroom, we can meet their needs.

Positive Pressure vs. Negative Pressure Cleanrooms: Similarities and Differences

When planning or preparing for a cleanroom installation, one of the most significant design considerations is whether it features a positive air pressure or a negative air pressure configuration. This factor relies heavily on the specifications of the intended application.

Positive Air Pressure Cleanrooms

A positive air pressure cleanroom has an air pressure level that is greater than that of the surrounding environment. This is achieved through the use of an HVAC system, which pumps clean, filtered air into the structure. When the door of the cleanroom is opened or if the cleanroom experiences a structural breach, the pressure disparity forces the clean air out rather than allowing unfiltered, potentially contaminated air in.

Positive air pressure cleanrooms are most commonly used in applications where keeping contaminants—such as dirt or debris—away from the contents of the cleanroom is critical. For example, it can be used to protect immunocompromised patients in hospitals or sensitive products such as microchips during the manufacturing process.

Negative Air Pressure Cleanrooms

In contrast to a positive air pressure cleanroom, a negative air pressure cleanroom maintains an air pressure level that is lower than that of the surrounding room. This condition is achieved through the use of an HVAC system that continuously filters air out of the room, pumping clean air into the room near the floor and sucking it back out near the ceiling.

Negative air pressure cleanrooms are used to keep contaminants contained within the enclosed work environment. If opened or breached, the pressure disparity forces air into the cleanroom, preventing contaminants from escaping. For the room to function properly, all windows and doors must be fully sealed and outtake filters must be installed.

This type of cleanroom commonly finds application in the biochemical, pharmaceutical, or medical industries. Industry professionals use it as an isolation chamber when testing or working with potentially harmful compounds and separating contagious patients to help prevent the spread of illness.

Similarities Between Positive Pressure and Negative Pressure Cleanrooms

Although the functions of positive pressure and negative pressure cleanrooms are quite different, they are some similarities between the two. For example, both types require the use of:

  • Powerful HEPA filters, which, along with the other HVAC system parts, need careful maintenance
  • Self-closing doors and properly sealed windows, walls, ceilings, and floors to facilitate the maintenance of appropriate air pressure levels
  • Multiple air changes per hour to ensure proper air quality and pressure conditions
  • Ante-rooms for employees to change into the required protective clothing and deliver the necessary materials and equipment
  • In-line pressure monitoring systems

Leave it to the Experts at Liberty Industries to Design & Construct Your Cleanroom!

Whether you need a positive air pressure or negative air pressure cleanroom, an experienced cleanroom manufacturer and distributor, such as Liberty industries, can ensure the design, development, and delivery of a solution that meets your needs. At Liberty Industries, our experts have full working knowledge of the entire cleanroom design and construction process, from cleanroom materials and best practices to the HVAC equipment needed for different types of applications. We also offer a variety of cleanroom accessories and equipment, including shoe brush machines, Tacky Mats ® and air showers.

No matter what type of cleanroom you need, we’re your one-stop shop to getting the perfect solution. For additional information about our cleanroom capabilities or to discuss your cleanroom specifications with one of our experts, contact us or request a quote today.