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By Jake Sanders and Ashley Merrill, Donaldson Integrated Venting Solutions
Incorporation of proper venting consistently emerges as a critical design consideration in the development of new products and enclosures. The need to prevent liquid and solid contaminants from entering enclosures, while still allowing gases to pass freely through these areas, means venting plays a key role in proper equipment operation. Well-designed enclosure protection vents (EPVs) guard sensitive devices and can also aid in extending the life of gaskets and seals used in enclosures.
Proper specification of venting solutions generally depends on three factors: ingress protection, airflow, and attachment method. All three are important, but any one of the three may become more important, depending on application, operating conditions, and other factors. To arrive at the best venting solution, a clear understanding of each factor is necessary, along with an integrated approach to determine the relative importance of each. An integrated venting solution (IVS) balances these factors to identify the optimum solution for each situation.
In evaluating venting solutions, one of the key parameters to consider is the ingress protection (IP) rating. Defined by International Electrotechnical Commission (IEC) Standard 60529, the IP rating is a two-digit number that indicates the effectiveness of sealing enclosures against intrusion from foreign bodies and moisture. The first number indicates protection from foreign bodies, such as moving parts, debris, and dust. The second number indicates protection level from moisture, such as drips, sprays, and submersions. Higher numbers indicate higher levels of protection.
For example, an enclosure that provides only protection from objects the size of a human hand and vertically falling water would have an IP rating of 11. An enclosure that provides full protection from dust and high-temperature, high-pressure water sprays would have an IP rating of 69k. Table 1 shows the various levels of IP ratings.
|IP||First Digit (Ingress of Solid Objects)||Second Digit (Moisture Protection)|
|0||No protection||No protection|
|1||Objects over 50mm (e.g., hands, large tools)||Vertically falling drops of water or condensation|
|2||Objects over 12.5mm (e.g., fingers, smaller tools)||Falling drops of water, if the case is tilted up to 15 degrees from vertical|
|3||Objects over 2.5mm (e.g., wire)||Sprays of water from any direction, even if the case is tilted up to 60 degrees from vertical|
|4||Objects over 1mm (e.g., fine wires)||Splash water from any direction|
|5||Limited protection against dust ingress (no harmful deposit)||Low pressure water jets from any direction; limited ingress permitted|
|6||Totally protected against dust ingress||High pressure water jets from any direction; limited ingress permitted|
|7||N/A||Short periods of immersion in water|
|8||N/A||Long, durable periods of immersion in water|
|9k||N/A||Close-range, high pressure, high temperature spray downs|
IP ratings provide a useful tool in matching venting characteristics with product needs. For example, the automotive lighting system shown in Figure 1 might be exposed to both dust and moisture, but not necessarily submersion in water, and merit an IP of 55 or 66. A consumer electronics device unlikely to be exposed to dust and water might merit an IP of 44. If an electronic device were intended to withstand more exposure to dust and possible submersion in water, the IP rating might be elevated to 67 or 68.
Various IP combinations can be made, based on operating conditions and cost factors. Diverse applications such as automotive, medical, packaging, and consumer electronics present unique environments that must be considered in the IP requirements. Also, a higher IP does not always provide the best solution; higher water protection can compromise airflow.
Along with IP rating, airflow requirements are critical in the vent selection process. Vents are typically designed to equalize the pressure inside and outside an enclosure. Higher airflow allows faster equalization and lower maximum pressure differentials. As pressure builds in a system, the weakest point will be found, so a properly designed vent takes the pressure off sensitive components and maintains proper airflow. Devices such as sensors in automobiles rely heavily on venting systems to equalize pressure for proper operation.
Factors to consider when determining airflow requirements include the total time to evacuate an enclosure and the operating pressures inside the enclosure. Proper ventilation helps minimize pressure differentials inside and outside an enclosure, with higher airflow vents reducing evacuation time and pressure differentials experienced by a system.
The rate of pressure change should also be considered. Pressure changes are often driven by temperature changes inside the enclosure due to changes in the environmental temperature, sunlight, heat generated by electronics, or moisture exposure. In some applications, pressure can be changed directly by compression of the enclosure, altitude change, submersion, chemical reactions within the enclosure, and other factors. As the rate of pressure change increases, higher airflow should be provided. Higher airflow can also provide other benefits, such as improving response time of electronic sensors inside enclosures.
While airflow requirements can be critical, they need to be balanced with ingress protection. As ingress protection is increased, airflow can be compromised, and vice versa. Proper venting solutions find the “sweet spot” of optimized airflow and moisture protection, as illustrated schematically in Figure 2.
Figure 3 shows how filter sizes and media affect pressure response. Two different vents of two different sizes, each placed on an enclosure experiencing an exponential 20-degree temperature change, exhibit different pressure differential over time. Generally, media with higher permeability provide greater airflow and lower pressure differential.
Another critical factor to consider in venting is the attachment method. Even with an appropriate IP rating and airflow specification, if the venting is not properly attached, the venting effectiveness can be compromised. Common enclosure protection vent attachment options include: Screw-Fit, Snap-Fit, Press-Fit and Weld-Fit (using either heat or ultrasonic techniques). A sampling of these options is shown in Figure 4.
Each attachment method has its merits in certain situations. Threaded EPVs can often be integrated into existing equipment such as protective cases, lighting enclosures, appliances, and other enclosures where protective venting is required and protection of the vent is necessary.
Snap-Fit EPVs can also be integrated into existing equipment and are useful when quick assembly is required. Certain Press-Fit EPVs, often used in electronic devices where space is limited, consist of a filtration membrane and a pressure-sensitive adhesive ring for securing the filter to the device.
In some cases, Weld-Fit enclosure protection vents can be incorporated directly into an enclosure in a vent assembly, as shown in Figure 5. This approach is often used in devices where adhesives are not appropriate, where chemical incompatibilities or extreme temperatures exist, or physical protection of the filter path is needed. This approach can also simplify assembly into the device. Weld-Fit combined with direct bonding injection molding are often used to attach venting materials in these situations.
Factors to consider when evaluating attachment methods include the composition of the material to which the vent is being attached, chemical compatibility, operating conditions such as temperature and pressure, and assembly conditions. Regardless of the attachment method, an integrated approach often provides the most efficient solution. If a vent supplier can provide an integrated venting solution, rather than a discrete vent that needs to be installed separately, designers and manufacturers can focus on the needs of their product and not the attachment method. Long-term cost and efficiency benefits can be realized if vents are properly attached and remain in service longer.
When evaluating the three key factors of venting, product designers and manufacturers need to consider all factors and identify which are most important for particular situations. IP rating, airflow, and attachment method may all play a part, with one or more factors carrying more weight in certain situations.
Filtration materials and characteristics may also figure into the equation. Specialized characteristics may include:
With the various factors to consider, an integrated approach is key to successful specification of a venting solution. Venting is not a one-size-fits-all process, and the factors may play different roles on different projects. The sooner the selection process can be undertaken in system design and the key factors evaluated, the more options will be available and the greater likelihood of success.
Ashley Merrill is the Global Product Marketing Manager for the Integrated Venting Solutions team at Donaldson Company. She has a BSBA from Drake University and an MBA from the University of Iowa. Ashley’s career includes 14 years of experience in the heavy-duty vehicle, automotive and chemical industries.