Venting--Protect telecom equipment enclosures from pressure buildup and contamination

Rugged environments can wreak havoc on telecommunications infrastructure equipment. This includes switching infrastructure components, terabit routers, cooling filters, base station cabinets, high speed cables for broadband signaling, and EMI shielding solutions that isolate RF and digital circuits.

A rugged environment is any environment that can potentially damage electronics. This can be outdoors, where the equipment is exposed to changing weather patterns and fluctuations in temperature.  It can also be indoors where high-pressure sprays are used to clean equipment, risking exposure to harsh chemicals, surfactants or liquids. It can also be inside the manufacturing facility or in the internal environment of the device itself, where a significant level of heat is generated during operation.

To protect the sophisticated electronics, most engineers design sealed enclosures with robust housing materials, durable seals, and strong bolts to ensure a tight seal. The enclosure is effectively airtight and waterproof, particularly if it must past Ingress Protection (IP) or National Electrical Manufacturers Association (NEMA) standards. Once the enclosure is installed in the field, however, it may begin to show evidence of water and particulates inside the housing. Watertight enclosures do not necessarily guarantee long-lasting protection and reliable performance because pressure differentials inside the housing put stress on the seals, which over time damages the seals and compromises the structural integrity of the housing.

It is crucial that network infrastructure nodes survive environmental exposure and maintain operational integrity.

Fig. 1 -- Rain, humidity, snow, ice and wind increase the likelihood that contaminants will enter an enclosure, leading to compromised performance or premature failure.

The Danger of Pressure Differentials

Even though designers and manufacturers may enclose the equipment in a rugged housing, incorporate gaskets, and seal all ports and connectors, there is still the "hidden" design challenge of pressure differentials.

The stress placed on seals and connection points is due to pressure differentials that occur again and again over time. This repeated expanding and contracting causes seals to fail. What causes pressure differentials? Temperature changes are the most common cause of failures due to pressure. The temperature change can be internal, external, or both. The electronics inside the housing generate a significant amount of heat, which can result in problems if the heat cannot dissipate. Externally, temperature changes can be dramatic – e.g., the temperature can differ by approximately 50° F (10º C) over the course of an average day in the desert.

Fig. 2 – Pressure differentials can cause pressure fluctuation,

pressure buildup, stress on seals, compromised seals and, ultimately, equipment failure, such as the contamination shown here.

Fig. 3 – Where do seals fail?

As shown in Fig. 3, failure due to pressure can erode component performance in numerous areas in a typical outdoor cabinet.  Design engineers usually think of openings as the weak points, so they install gaskets to improve the seals; however, other areas like those around screw heads, indicator lights, and wire conduits are also sources of potential leaks. Figure 3 shows the various seal locations and connection points where water and contaminants can enter a tower-mounted amplifier when a vacuum occurs.

Pressure must be equalized. Increasing the durability of the seal is easy to implement but provides no pressure equalization and increases costs.   Hermetically sealing the vents is expensive and labor-intensive as to be unrealistic.

The better solution is installing a vent that allows air and gases to flow freely in and out of equipment housings and that can virtually eliminate the stress and damage on housing seals.

The ideal solution is vents with a membranous construction and a microporous structure that allow gas molecules to pass through the membrane to equalize pressure while, at the same time, repel liquids and particles that can cause corrosion and contamination. Vents made with an expanded polytetrafluoroethylene (ePTFE) membrane allow continuous pressure equalization while still maintaining an environmental seal. Expanded PTFE is a unique, microporous membrane that is inherently waterproof, with a unique node-and-fibril microstructure that permits gas molecules and vapors to pass through it easily, but with openings so small that liquid and other particulates are repelled.  The result is pressure equalization without contamination.

Fig. 4 – ePTFE membrane

The benefits of this type of venting include improved reliability, reduced manufacturing costs, relief from condensation, minimal maintenance and the flexibility to easily seal to a variety of housings.

Fig. 5 –The rugged, single-body-design of the screw-in vent shown here (left) incorporates a chemically inert, UV-resistant ePTFE membrane that withstands operating temperatures ranging from -40°C to 125°C. It is engineered with a robust plastic that prevents damage from mechanical impact and other environmental factors and is available in various sizes and thread types.

About the Author

Jason Zambotti has worked with W. L. Gore & Associates’ Protective Venting business for more than eight years, most recently as the global leader of the telecommunication venting team. Jason consults with customers to solve some of the most challenging design issues of ruggedized telecommunications equipment. Jason holds a B.S. in mechanical engineering from Pennsylvania State University and is currently pursuing an MBA at the University of Delaware.