A hermetically sealed power supply uses airtight enclosures (typically welded metal, glass, or ceramic) to completely prevent gas, moisture, or contaminant ingress. In contrast, environmental sealing uses gaskets or seals to provide protection against dust and water but is not airtight. Understanding how to properly define hermetically sealed systems versus environmentally sealed systems is crucial for selecting the right protection level for your power supply application.
If a power supply needs protection from its environment, it’s important to use either environmental or hermetic sealing. In applications in which protection from dust or water particles is necessary, environmental sealing is sufficient. However, in applications in which air or gas tightness is required, hermetic sealing is the stronger option. It’s essential to understand the difference between environmental and hermetic sealing, as well as the applications and benefits of each, to make the right selection for your purposes.
Quick Navigation:
Hermetically sealed is an enclosure with zero permeability to gases and liquids over an extended period of time. The term hermetic originates from Hermes Trismegistus, the legendary alchemist who was said to have sealed vessels so perfectly that their contents remained unchanged indefinitely.
When engineers define hermetically sealed systems, they refer to enclosures that achieve airtight and gastight barriers through:
Hermetic Sealing Materials:
The key difference when you define hermetically sealed versus environmentally sealed:
An environmental seal, usually composed of rubber (such as silicone or EPDM gaskets), acts as a barrier between the power supply and its environment. Environmental sealing helps prevent contaminants from breaching the power supply. This seal maintains the equipment’s electrical performance and is necessary for effective, safe equipment operation in many settings. An environmental seal is adequate when dust or water particles are a concern, but airtightness is not required.
Environmental Sealing Standards:
Unlike hermetically sealed enclosures, environmentally sealed units use mechanical compression of gasket materials rather than permanent bonds. This allows for field servicing but does not provide the complete isolation achieved by hermetic sealing.
For such machinery to operate in an effective, safe manner, you must prevent infiltration of contaminants within electrical components. Dust, dirt, water, and other similar particles could damage the internal system, causing malfunction. Such malfunction could render the equipment unusable and present a safety hazard or require maintenance and repairs. Environmental seals keep this from happening.
Environmental sealing has critical benefits for the above applications. An environmental seal:
The term hermeticity refers to the state of being airtight or gastight, meaning air and gas cannot escape the system. Hermetically sealed products, usually composed of glass, ceramic, epoxy or fluoropolymers, can withstand the highest pressures. Based on the definition of hermetically sealed, a system is hermetically sealed if contents cannot leak in or out over an extended period of time.
Hermetic sealing is important for vacuum processing, pressure vessels, and underwater-immersed devices. The most appropriate material depends on the application. For example, some applications require the least possible added weight, which would make an epoxy seal more appropriate than a heavier glass seal.
It’s possible to calculate a hermetic seal’s effectiveness as a leakage rate value, which refers to the amount of gas flowing through the seal per second. The more contents can leak through the barrier, the less effective it is. You can quantify leak ratings with the unit mbar L/s (millibar liters per second) for liquids or atm cc/s (atmosphere cubic centimeters per second) for gases.
Hermetic sealing is important for:
The most appropriate hermetic sealing material depends on the application. For example, some applications require the least possible added weight, which would make an epoxy seal more appropriate than a heavier glass seal. Military avionics often use welded aluminum or stainless steel hermetic enclosures to minimize weight while achieving complete hermeticity.
It’s possible to calculate a hermetic seal’s effectiveness as a leakage rate value, which refers to the amount of gas flowing through the seal per second. The more contents can leak through the barrier, the less effective it is. You can quantify leak ratings with:
Hermetic seals are tested using helium leak detection methods per MIL-STD-883 (for microelectronics) and MIL-STD-202 (for component testing). These stringent tests verify the seal will maintain hermeticity over the product’s entire service life.
Because they can withstand such high pressure and provide complete environmental isolation, hermetic seals are well-suited for a wide range of critical applications. Any application requiring air- and gas-tightness benefits from hermetic sealing. It can help protect equipment in the toughest settings or preserve goods, extending a product’s lifespan in storage.
Examples include aerospace applications, as well as military and deep offshore applications. Hermetic seals are also necessary for some types of packaging, such as pharmaceutical and food preservation packaging, using vacuum compression or canning. In addition, passive houses and zero-energy building techniques often incorporate hermetic seals to create more energy-efficient structures. Hermetic sealing is also used to preserve artifacts, such as the United States Constitution in Washington, D.C.
A hermetic seal has many benefits for its relevant applications thanks to its airtight and gastight quality as well as its durability. When you define hermetically sealed enclosures for power supplies, these benefits become critical for mission success in extreme environments. Here are some of the reasons an application might require a hermetic seal.
The two ways gas can permeate a barrier are through leakage or diffusion. Leaks require material defects, such as a crack in the barrier. Such imperfections can cause the device’s failure. Diffusion is a natural process resulting from pressure difference. Gas can migrate through solids, regardless of existing defects. Off-gassing, or desorption, is the release of gas from a solid material. You may have heard of off-gassing in reference to volatile organic compounds (VOCs) escaping from household furniture.
The rate of leaking, diffusion and off-gassing depend on the size of the gas molecules in question. Smaller gas molecules are likelier to penetrate a surface. For instance, rates of penetration are higher for tiny helium molecules than larger nitrogen molecules. A hermetic seal can help reduce rates of both diffusion and off-gassing. The seal’s material is the main influencing factor, while rubber and plastic often allow for high levels of diffusion, stronger materials are more limiting. In many cases, a fluoropolymer, glass or epoxy hermetic seal is appropriate.
A virtual leak occurs when a gas becomes trapped between the assembled components of a system. The gas could get caught between bores, screws, blind holes, or other working parts, posing a risk of system deterioration or contamination of the internal atmosphere. Virtual leaks are particularly problematic in vacuum systems and hermetically sealed packages. Hermetic seals minimize the risk of virtual leaks in addition to other types of leaks through proper design practices:
Many of the applications in which hermetic sealing is necessary involve extremes in pressure and altitude. For instance, avionic and related equipment require operation at high altitudes (up to 80,000 feet) with extremely low external pressure. Similarly, deep offshore equipment must withstand some of the most extreme high-pressure environments on Earth (>10,000 psi in deep-sea applications). Hermetic seals are designed for such applications. They can withstand the lowest and highest pressures and altitudes.
Pressure/Altitude Protection:
Stabilizing pressure on both sides of the system through pressure-compensated designs or maintaining internal pressure helps to minimize diffusion and mechanical stress on the hermetic seal.
Such relevant environments are often home to extreme temperatures. Both deep-sea and atmospheric conditions involve extremely low temperatures (down to -55°C or lower). Meanwhile, rapid-moving equipment and aerospace systems must withstand extremely high temperatures (up to +125°C or higher for avionics, +200°C or higher for downhole oil/gas equipment).
Hermetically sealed power supplies at ACT are designed to meet MIL-STD-810 temperature requirements:
The hermetic seal materials (welded metal, glass, ceramic) maintain their integrity across these temperature extremes, unlike elastomer gaskets which can harden, crack, or lose compression set.
While environmental seals are appropriate for everyday applications, hermetic seals can protect equipment in Earth’s harshest environments. Whether related to extreme temperature, extreme pressure or extreme altitude, a harsh environment necessitates a hermetic seal.
Both environmental and hermetic sealing help protect a system from damaging particles, but understanding when to define hermetically sealed requirements versus environmental sealing requirements is critical for system reliability. Advanced Conversion Technology (ACT) frequently uses environmental sealing to achieve IP67 ingress protection rating on its commercial and industrial products, while our military-grade power supplies can be designed with hermetic sealing for the most demanding applications.
ACT Sealing Capabilities
Power supplies of any application may require one of these sealing technologies. While environmental seals are sufficient for many applications, hermetic seals provide necessary protection in the most extreme, harsh environments. A hermetic seal is also used for high-voltage power supplies (voltages typically greater than 10 kilovolts (kV) and currents in the microamp range) to limit arcing as well as environmental impacts.
If you’d like to learn more about environmental and hermetic sealing for your power supply, contact us at Advanced Conversion Technology. At ACT, we offer military-grade, flexible and customizable power supply solutions, and we’ll help determine what would suit your needs.
Explore our sealed power supply solutions: