Pressure switches fail when moisture gets inside. This happens in offshore platforms, chemical plants, and other harsh environments where standard weatherproof enclosures cannot keep water out. Hermetically sealed switches solve this problem through fusion welding that creates permanent barriers against moisture, extending switch life 5 to 10 times compared to gasket-sealed alternatives.
What Hermetic Sealing Means
Understanding the definition helps explain why hermetic sealing outperforms alternatives.
The National Electrical Code Section 500.2 defines hermetically sealed as equipment sealed against the external atmosphere where the seal is made by fusion, such as soldering, brazing, welding, or glass-to-metal fusion.
Two methods create hermetic seals:
- Metal-to-Metal Fusion Welding seals the switching element inside a stainless-steel capsule through precision welding. The weld creates a continuous, gas-tight seal with no gaskets or mechanical fasteners. The fusion weld forms a molecular bond that eliminates leak paths.
- Glass-to-Metal Seals provide electrical isolation and hermetic protection where connections pass through the barrier. These seals use controlled heating to fuse borosilicate glass to metal conductors and housings at temperatures exceeding 1000°C. Matched seals and compression seals each offer different temperature capabilities and application benefits.
Why Hermetic Sealing Beats Gasket Protection
The Gasket Problem
Gaskets degrade over time. Temperature cycling, vibration, and chemical exposure all compromise seal integrity. Field data from offshore installations shows gasket-sealed enclosures experience moisture intrusion within 18-36 months despite intact external appearance.
Complete Environmental Isolation
The fusion-welded metal capsules create permanent barriers. The industrial hermetic seals allow less than one gram of water vapor per year to pass through. Whereas gasket-sealed enclosures allow tens or hundreds of grams annually.
Metal-to-metal and glass-to-metal fusion seals do not degrade from temperature cycling, vibration, chemical exposure, or UV radiation. Accelerated life testing shows zero performance degradation after thousands of temperature cycles that destroy gasket seals.
Wider Operating Ranges
Gasket materials limit operating temperature. Different gasket compounds work at different ranges, but all have limits. Hermetic seals operate across much wider temperature ranges, eliminating temperature-related failures. They also withstand extreme differential pressures because the fusion weld distributes stress across the entire capsule. These technical advantages translate to specific industry benefits.
Where Hermetically Sealed Switches Work Best
Offshore Oil and Gas
Salt spray, high humidity, temperature cycling, and continuous vibration attack standard switches. Hermetically sealed switches provide the reliability offshore installations require. Compact designs save valuable space on crowded skids while combining hermetic protection with explosion-proof ratings.
Field experience from North Sea platforms shows hermetically sealed switches average 12-18 years of service with low failure rates. Gasket-sealed switches in the same locations average 18-24 months with much higher failure rates.
Chemical Processing
Chemical plants contain corrosive gases that attack electrical contacts through gasket-sealed enclosures. Hermetically sealed switches completely isolate contacts from these atmospheres. Material selection matches specific corrosive compounds. Therefore, temperature switches with hermetic protection handle high-temperature processes while protecting electrical contacts from corrosive vapors.
Marine Vessels
Marine vessels operate in saltwater environments with constant humidity. Hermetically sealed switches resist seawater corrosion for the life of the vessel. Classification societies require hermetic sealing for emergency and safety-critical systems. The switches eliminate maintenance calls and extend drydock intervals.
Power Generation
Power plants need switches that handle extreme temperatures and provide decades of reliable service. Nuclear facilities require special qualifications. Fossil fuel plants use hermetically sealed switches in outdoor switchyards, cooling towers, and fuel handling systems, where they resist weather exposure and corrosive flue gas condensate.
Wastewater Treatment
Wastewater facilities expose switches to hydrogen sulfide and other corrosive gases. Outdoor installations face weather exposure combined with corrosive atmospheres. Hermetically sealed switches provide decades of service in digester areas where standard switches fail within months. Maintenance cost reduction reaches 70-80% compared to gasket-sealed alternatives.
Material Selection for Your Environment
Standard stainless-steel capsules resist corrosion in most industrial environments. Different grades provide different protection levels. Offshore and marine environments typically require higher grades for long-term reliability.
Some environments exceed standard stainless-steel capabilities. High-nickel alloys resist strong acids and high-temperature corrosive gases. Nickel-copper alloys resist specific acids and seawater. Titanium provides exceptional strength at low weight while resisting chlorides. Advanced stainless-steel grades offer higher strength and better chloride stress corrosion cracking resistance.
Making the Right Choice
Choosing the correct hermetically sealed switch requires matching capabilities to application requirements. Start with operating pressure and temperature ranges. Consider both normal conditions and potential overpressure events.
Evaluate environmental severity. Salt spray and high humidity require different protection than indoor environments. Corrosive gases require material selection based on specific compounds and concentrations.
Match electrical ratings to control circuit requirements. Consider voltage, current, and whether the load is resistive or inductive. Different contact materials handle different signal levels and current ranges.
Determine hazardous area classification. Explosion-proof ratings allow installation where explosive atmospheres exist. Hermetically sealed switches with maximum ratings work in most hazardous locations.
Safety instrumented systems require proven reliability metrics. SIL certification verifies switches meet requirements for safety applications. Hermetically sealed switches typically carry SIL 2 certification for non-redundant use.
The Total Cost Picture
Hermetically sealed switches cost more than gasket-sealed alternatives upfront. The value comes from extended service life and reduced maintenance.
Total cost analysis includes multiple factors. Consider replacement frequency, maintenance labor, downtime costs, and safety incident risk. Each replacement requires scaffolding or access equipment, labor, process shutdown, and recommissioning. In addition, production deferment during unplanned shutdowns often exceeds all other costs.
A switch that costs more initially but lasts three times longer with minimal maintenance provides significant savings over its lifetime.
Selecting hermetically sealed switches requires understanding your specific environment, operating conditions, and reliability requirements. Manufacturers with decades of field experience in harsh environments provide the engineering support needed to match switch capabilities to your application.
SOR Hermetically Sealed Switch Solutions
SOR Controls Group has manufactured hermetically sealed switches for over 50 years. Our Mini-Hermet and Big Hermet product lines work in the world’s harshest environments, from offshore platforms in the North Sea to chemical plants processing corrosive materials.
SOR pioneered the Static O-ring pressure-sensing technology, allowing compact hermetically sealed designs. Hermetically sealed capsules come in stainless steel or exotic alloys matched to specific corrosive environments. Explosion-proof ratings combine with hermetic protection in single packages.
Custom configuration matches exact application requirements. We have maintained our ISO 9001 certified manufacturing since 1993, representing our consistent quality. Three-year warranties back hermetically sealed products. Our global manufacturer representative network provides local support and application support.
Explore SOR Hermetically Sealed Switch Options:
- Hermetically Sealed Pressure Switches
- Hermetically Sealed Differential Pressure Switches
- Hermetically Sealed Temperature Switches
Ready to discuss hermetically sealed switches for your application? Contact your local SOR manufacturer representative.
