Protecting Your Equipment, Protecting Your Environment
Published in Blower & Vacuum Best Practices: September 2020
In a world increasingly reliant on vacuum technology, the consequences of not protecting a vacuum system or its surrounding environment can be costly. For decades, vacuum pumps have enabled new technologies and processes to evolve in rapidly advancing industries such as food processing, pharmaceuticals, electronics, solar, semiconductor, and many more. These processes generate various contaminants that can cause catastrophic vacuum pump failure when ingested. Furthermore, toxic process contaminants must not be exhausted into the surrounding atmosphere due to health and safety concerns. When operating a vacuum system, careful consideration to inlet and exhaust filtration is critical in protecting both your equipment and your environment.
In this article, we discuss both vacuum pump inlet and exhaust filtration and explore how protecting your vacuum pump can increase productivity and help businesses reach their sustainability objectives.
Vacuum Technology and Filtration
A vacuum pump is used to pull air from a process or closed system and will frequently encounter contamination from the process. As the pump pulls air out of the system, it exhausts that same volume of air to atmosphere. Vacuum principles show that as process vacuum level increases, mass flow through the pump decreases.
Process flow rate, vacuum level, temperature, and vapor pressure, all interact to pose a tremendous challenge when developing vacuum filtration solutions. Vacuum level can also affect the physical properties of a contaminant such as boiling point. A change in boiling point can cause a phase transition from liquid to vapor further increasing complexity with the filtration and separation selection process. Understanding the critical interactions between all variables is essential to the success or failure of a filter or separator.
There are two competing priorities when designing an effective vacuum system. The first is adequately protecting the vacuum pump from the process. The second is optimizing system performance over an extended time period. When designing a vacuum system, filtration should be at the forefront of the design process so field issues can be minimized. Properly identifying the contaminant type and load up front ensures the proper filtration technology is deployed. This is critical to ensuring system optimization.
Vacuum Pump Inlet Filtration
Vacuum filtration and separation is an art just as much as it is a science. The concept of filtration and separation is quite simple: remove any contaminant from an air or gas flow before the contaminant can enter a piece of equipment. However, contaminant removal becomes extremely complex when vacuum conditions and multiple process variables exist.
Ultimately, the purpose of an inlet vacuum filter is to protect the pump from the process. A typical particulate filter consists of a media, like paper, that air must pass through to be cleaned. Many types of particulate removal media exist, all of which have varying micron ratings and removal rate efficiencies. They have different physical and chemical properties which make them suitable for different operating conditions and applications. Paper, polyester, polypropylene, HEPA, ULPA, and PTFE are commonly used filtration medias. Other media types can include adsorbents such as activated carbon and activated alumina or coalescing medias which usually contain fiberglass and are proprietary in nature.
It is worth restating that many vacuum processes are extremely complex. Involving a trained filtration expert early in the design and specification process can prevent costly mistakes caused by “self-selecting” a standard filtration product for a complex vacuum application.
Types of Contaminants
Anything other than clean air entering the inlet of a vacuum pump or exiting the exhaust can be harmful. There are three primary contaminant types that require meticulous review as each can react very differently under vacuum conditions.
Particulate is the most common contaminant that can damage a vacuum pump. Particulates can be abrasive and come in many solid forms with the most common being powder, dust, sand, or large mass. Most particulates are non-reactive and a standard vacuum filter is suitable for these applications. However, there are applications, such as chemical vapor deposition, metallurgy, and silicon crystal growing in which particles can be dangerously reactive if exposed to oxygen or other reactive agents. Under these circumstances, adding a standard vacuum inlet filter to the system may not offer the appropriate protection for the equipment or employees. When volatile particulates are present, specialty medias and features like oxidation ports, collection tanks, and specialty filtration media are necessary to ensure adequate protection for vacuum systems and the workers that interact with the equipment.
Liquid can be much more difficult to stop from entering a vacuum pump as it can be present in a variety of forms: slugs, droplets, or aerosols. (Not a vapor.) Effective liquid removal systems include different mechanisms such as baffles, demister pads, and low velocity expansion chambers, to effectively separate the liquids in these different forms. If a vacuum pump ingests enough liquid from a process, it will essentially flood the pump causing a catastrophic failure very quickly. Liquid contaminants include water, solvents, oils and various chemicals. Applications with extremely high volumes of liquids require constant maintenance of the liquid removal filter. In these circumstances, an automatic draining system can be integrated with the filter to minimize maintenance and maximize production runtime.
Vapor is the most elusive and difficult to capture of the three contaminants. As a process begins to operate at deeper vacuum conditions, liquids will transition into a vapor phase. To avoid ingestion by the pump, this vapor must be condensed back into a liquid state so there is a better chance of recovery. In order to condense vapors, a significant temperature reduction Delta (ΔT) must be introduced so vapor can transition back to a liquid state. The required ΔT is based on a liquid’s vapor pressure and system’s dew point. Effective separation can be accomplished by using multi-stage vapor condensing and filtration technology which provides “cold” surfaces for condensing to occur. For trace amounts of vapors coming from a process, adsorbent technologies can be deployed as effective alternatives to condensing technologies.
Vacuum Pump Exhaust Filtration
For complete optimization of a vacuum system to occur, the exhaust side of the vacuum pump must also be addressed up front to minimize field issues.
The purpose of an exhaust filter is to protect the environment from the equipment. Properly addressing contaminants at the inlet of the vacuum pump is the best strategy for minimizing issues at the discharge. However, there are applications that require additional care with discharge air quality such as food preparation/packaging, medical vacuum systems, electronics manufacturing and research facilities. These applications may require multiple stages of filtration to meet strict air quality requirements for the work environment.
An OEM’s wet technology vacuum pump package will generally offer adequate performance for light- to medium-duty applications that have low levels of oil carry over and odor. However, environments with zero tolerance for these issues, such as laboratories and hospitals, will need high-performance oil coalescing filters to keep the environment significantly cleaner and odor free.
Other instances where additional exhaust filtration would be appropriate include oil-sealed pump technologies with frequent cycling to atmosphere or pumps that run at higher temperatures. Under these circumstances, piping configuration and placement of the oil mist exhaust filter can have a significant impact on the vacuum system’s performance. Again, involving a trained filtration expert early in the design and specification process can prevent costly mistakes.
A Complete System
As innovative industries continue using vacuum technology to grow and evolve, reliable and complete vacuum systems are essential for continued success and sustainability. Filtration is often an afterthought, and when there is a problem, an emergency fix can be costly and stressful for those involved.
A vacuum pump system is incomplete without the proper filtration and separation protection. When considering all the process variables and potential filtration options, properly protecting a vacuum pump can be a challenge. Working with vacuum filtration experts in the early stages of design and specification will save money and prevent countless future hours of frustration for engineers and operators. Not only will the proper filtration and separation solution help users save on maintenance costs and energy consumption, it can help improve worker safety and morale with consistent process up-time and higher quality outputs. Whether protecting the pump or protecting the environment, implementing the right filtration and separation technologies will complete the system.
About the Authors
Clint Browning is Vice President of Sales & Marketing, Solberg Manufacturing, and Mike DeLisi is responsible for Vacuum Technology for the company. With their combined filtration experience of more than 35 years, they have helped some of the largest companies around the world select the right filtration and separation solutions.