In the process industry, some pressure switch manufacturers point to agency listings as proof of their product quality, rather than the product design. Approvals and certificates are important, and while they do indicate suitability for use in specific application conditions, it is ultimately the product design that determines reliability. When it comes to mechanical pressure switches, that design belongs to SOR Measurement and Control, and this year marks 80 years since the company opened its doors.
Roy Dunlap started his machine shop in 1946 with $2,000 and one employee. Ten years later, while at a diner, Dunlap overheard oilfield workers complaining about their pressure switches. Existing switches used a moving O-ring seal, and that movement quickly wore down the sealing integrity, causing the switches to fail. Workers kept having to pull their pressure switches apart to fix or replace them. Dunlap took the problem to Ben Brown, a physics professor at the University of Kansas. The two set out to design a pressure switch that would solve this dilemma. Their design used a static O-ring instead of a moving one. A “static” O-ring is fixed in place, eliminating the wear and tear from friction during movement. That single change solved the primary issue that was causing most switch failures at the time.
The design worked so well that Dunlap renamed his company to Static-O-Ring after the technology, which he later shortened to SOR. The static O-ring design became the starting point for a pressure switch platform that SOR continues to manufacture to this day.
The Proof is in the Performance
The SOR Measurement and Control pressure switch is designed for lasting performance by minimizing the number of moving parts that could fail. A pressure switch failure can trigger a shutdown or a safety event. Fewer moving parts wearing down means fewer field replacements, resulting in fewer unplanned shutdowns. Industrial processes running around the clock depend on that degree of consistency.
Since its introduction into the Oil and Gas market, SOR has grown its pressure switch offering to meet the requirements of other industries. By adding options such as hermetically sealed switching elements, welded diaphragms, and configurations built for extreme temperatures and pressures, SOR expanded into chemical processing, power generation, and other process applications. However, the core design mechanism, a static O-ring seal, has remained the same throughout the company’s history.
Although the world of process instrumentation has continued to evolve, mechanical pressure switches still have an important role to play in measurement and control systems. The SOR mechanical pressure switch actuates using a diaphragm and piston assembly that responds directly to process pressure. It requires no electricity to sense the condition or trip the switch. A mechanical switch keeps monitoring process pressure even when a PLC, a DCS platform, or the power itself goes down. Plants often specify one as a standalone device or as a redundant backup alongside an electronic pressure transmitter.
SOR Mechanical Pressure Switch Types
The SOR story didn’t stop with the initial pressure switches, and their offering grew to include switches for vacuum, differential pressure, and temperature.
Pressure and Vacuum Switches monitor process pressure directly. They trigger an alarm or shutdown when the process pressure reaches a set threshold. SOR builds this type for primary and redundant pressure duty across a wide range of industries. Published applications include pump protection and compressor monitoring.
Differential Pressure Switches are analogous to their gauge and vacuum counterparts, but instead compare pressure at two points instead of one. Filter monitoring, pump alarms, and flow verification are some of the essential applications for DP switches. A binary on/off signal is enough to flag a clogged filter or confirm flow across a restriction or primary orifice.
Temperature Switches are similar to pressure switches but instead of actuating via process pressure, they use a vapor-pressure thermal system. Fluid contained in a sensing bulb expands or contracts with process temperature and actuates the switch at the set point. SOR temperature switches are used on heat exchangers, fired heaters, lubrication systems, and tanks. They support functions like high-temperature shutdown and lube oil overtemperature protection.
Most of these switch types are available as hermetically sealed, explosion-proof, or weatherproof. Pressure, differential pressure, and temperature switches are also available in nuclear-qualified versions.
Keeping Up with the Times
An SOR pressure switch installed on a process line today still operates using the same static O-ring design principle. That core design solved an oil tank overflow problem seven decades ago; the improvements since then have kept it as a viable solution for pressure measurement applications.
None of that history means the product line stands still. Despite the static o-ring being a revolutionary design mechanism in 1956, that does not guarantee survival to 2026. It survives because each decade of use revealed opportunities for design improvement, and over time any identified weaknesses got engineered out. SOR continues to expand options and configurations to meet demands the original 1956 switch never faced.
Frequently Asked Questions
Q. Can SOR build a custom switch for my application?
A. SOR offers Engineered-to-Order product solutions for unique process requirements and challenging applications. Submit your details through the Request a Quote form for help finding a suitable model number for your specific application.
Q. Where are SOR switches manufactured?
A. SOR Measurement and Control switches are engineered and manufactured at the company headquarters in Lenexa, Kansas.
Q. What is the difference between a hermetically sealed, explosion-proof, and weatherproof pressure switch?
- A hermetically sealed pressure switch utilizes a switching element in a welded capsule. Because the switching element is sealed, the electrical connections are isolated from the process media. This results in hermetically sealed pressure switches that are inherently explosion-proof while also permanently guarding the switching element against moisture and corrosive atmospheres.
- Explosion-proof pressure switches use housings designed to contain internal sparks or electrical arcing, preventing them from igniting gas or dust in the surrounding atmosphere.
- Weatherproof pressure switches use housings that protect against rain and general outdoor exposure. They are not suitable for use in hazardous locations.
- It is possible for a single pressure switch to have more than one of these ratings. For example, a hermetically sealed pressure switch can also be explosion-proof.
Next Steps
Check Out Our Application Notes: See how plants in your industry use SOR pressure switches to solve real process problems.
Request a Quote: Send your application details to our team. They will bring in an engineer when your application calls for it.
