Magnetically actuated pack-less valves go back 75 years, to Ralph Carlson’s work at Crane in the early 1940s. Yet despite the allure of a stemless valve operated solely by magnets, and the ideas being revisited in every decade since, magnetically actuated valves caught on only in a few niche applications, given the expense and delicate nature of suitable high-strength magnets prior to the late 90s/early 2000s. However, even since the advent of relatively inexpensive Neodymium Iron Boron magnets in the past 20 years, with applications from motors for electric cars to children’s toys, magnetic valves have not progressed as far as their proponents hoped.
While acknowledging that there have been several key reasons for this lack of progress, these problems are surmounted with a new technology that overcomes past hurdles like potential failure at high temperatures, stuck valve conditions, corrosion, demagnetization events, static service seals, and older port connections that negated many of the potential advantages of magnetic valves.
Neodymium Magnets.
Samrium Cobalt Magnets.
Troubleshooting Limitations of Previous Magnetic Valves
There has always been a tradeoff with magnets between magnetic strength, temperature performance, corrosion resistance, robustness, and cost. It was not a game of being able to choose any 4 out of 5, because all the available choices involved severe compromise. A patented approach has been developed to get the magnets out of the valve body so they do not fail on the inside, whether from temperature, corrosion, or fluctuating magnetic fields. Magnets now can be selected on the basis of what they must accomplish magnetically, independent of compatibility with working fluids or operating temperatures.
Anyone experienced with valves in real-world environments knows they get stuck. With a straight mechanical linkage, such as a traditional valve stem, one can force a valve to unstick, though this can be ill-advised. Magnetically actuated valves that have a specified operating torque designed not to be exceeded, may overcome the problem of the overzealous operator who otherwise could damage a delicate valve seat or expanding gate or bend the valve stem by going Neanderthal on it. On the other hand, a set torque limit can spell disaster when faced with a corroded valve handling a sticky fluid that’s been closed for several months. The practical magnetic valve must offer asymmetric torque into, versus out of, a seated state, in order to overcome stuck valve conditions, typically 20% over-torque as a minimum, with perhaps an optional set of cheater handle approaches where customer applications allow.
As corrosion and material compatibility are always considerations in industrial, petrochemical, steam, and marine valve applications, removing the magnets from the enclosed valve body goes a long way towards alleviating corrosion issues too. It is easier to mitigate, monitor, and control corrosion if it only occurs in the actuator external to the valve body. In the event that an anticorrosion coating or treatment is damaged, for example, it is much more evident when it occurs outside the sealed bonnet, where the external actuator can be repaired or replaced without disturbing the balance of the valve — often while the valve is still in operation and the bonnet remains sealed.
While demagnetization events may occur from a handful of causes, the most common involve exceeding the operating temperature of the magnets where degradation begins to occur (or worse, the Curie temperature where total demagnetization can happen), or because of coercivity issues, as for example, with AlNiCo magnets, whereby external magnetic fields degrade the magnet. Again, these situations can best be managed externally, and if they do occur, by repairing or replacing the actuator without impacting the rest of the system.
The three most likely candidate magnets for magnetic valves are Neodymium Iron Boron (the most powerful type of magnet currently available), Samarium Cobalt (a previous generation of rare earth magnet somewhat less powerful, and much more expensive, but with a higher operating temperature range), and AlNiCo magnets that can operate at extremely high temperatures, but have low coercivity and hence need special handling such as keeper bars to avoid demagnetization. All have their potential applications. But by getting the magnets out of the core, the most compelling value proposition will often be higher strength, lower cost for a given field strength, and a denser footprint of Neodymium magnets, provided one is careful to coat them against corrosion and locate them sufficiently far from very high temperature operating fluids / bonnets.
Finally, early generations of magnetic valves necessitated a static service seal to access the internal magnets, in case they suffered damage or corrosion. Their temperature limitations precluded hermetic sealing of the bonnet via welding or brazing, and also prevented welded, soldered or brazed port connections. These drawbacks negated many of the potential benefits of magnetic valves, since at a certain point, a collection of static seals might prove nearly as problematic as a single dynamic seal. With the inert valve core, magnetic valves can now be welded or soldered in place, and the bonnets hermetically sealed. There simply is no leakage path associated with the valve anymore. And by designing the network of valves in a probabilistic manner, one can virtually guarantee no leaks in a valve network over its entire operating life.
Installed Valve.
Removable Handle.
Path to a Breakthrough
Dr. Davis became interested in magnetic couplings after winning an STTR research contract with the US Navy in 2008, for an ocean wave energy harvesting machine to power small buoys. His original machine had a rotating seal very similar to the packing around a valve stem. After being immersed in sea water, baked in the sun on the deck of the
research vessel, ingesting sand and buffeted by waves — in short, all the rigors of ocean deployment — the rotating seals invariably developed leaks. Knowing there had to be a better way to seal the machines, he thought of the magnetic stirrers for laboratory hot plates, and ultimately built a wave energy machine containing a magnetic coupling.
These magnetic couplings led to other applications for the Navy, such as magnetic gear trains for sonar systems, fiber optic rotary joints, and in 2010, a contract with the Navy for a previous generation of a magnetically actuated valve.
These earlier generations of magnetic valves exhibited all the unfortunate operational constraints described above that prevented their catching on for broader applications. They contained magnets on both sides of the magnetic coupling, hence on both sides of
the sealed interface, which is problematic for a number of reasons: Modern neodymium magnets have fairly low operating and Curie temperature limits, beyond which they lose their magnetism, meaning that internal magnets typically preclude usage in higher temperature applications and steam handling systems. Neodymium magnets, in particular, often expand, flake, and disintegrate as they corrode, potentially causing a stuck valve position without prior visual warning (since one set of magnets is enclosed in the bonnet).
Worse yet, a valve containing internal magnets still requires a static seal on the bonnet, because the magnets themselves will not tolerate the heat from the valve being soldered or welded to pipes, making for the likelihood of at least 3 statically sealed connections associated with each valve. AlNiCo magnets can operate at a higher temperature, but are not as strong as neodymium magnets, are temperamental in handling and storage (often requiring a keeper bar to preserve their magnetism when not in use), and thus not practical for most applications out in the field. Either type of magnet needs to be coated for use inside the valve / fluid compatibility and is subject to internal corrosion (often severe) if the coating were to deteriorate or fail.
Magnetic chucks for machine tools do not really mind how hot the work piece gets during machining. The magnets are enclosed deep within the chuck and the clamping force is switched on and off like a circuit. Similarly, instrument and optical mounts contain the magnets — whereas the table they attach to does not, and these systems are quite strong. The completed magnetic circuits develop tremendous forces, and those forces can be released just by turning a dial and disconnecting the magnetic flux path.”
Dr. Davis built an initial actuator prototype using a modified C-clamp and a couple of magnets and the initial prototype worked. US Patent Number 9,797,521, for a Rotary Magnetic Coupling Actuated Valve with External Magnets and Internal Magnetic Flux Path, was issued to Dr. Davis on October 24, 2017.
Evolution of Magnetic Valve Prototypes.
Prototypes from 8 Years of Magnetic Valve Research.
The Invention
The new magnetic valve actuator works by keeping magnets outside the sealed valve enclosure and providing a magnetic flux path that completes a magnetic circuit through the inside of the valve enclosure. It can operate at far higher temperatures than previous approaches without employing AlNiCo magnets, the valve bonnet can be sealed (hermetically if desired), no internal valve maintenance is required (all internal components are inert), there is no more potential for corrosion of magnets inside the valve, no special handling of the magnets is required, the valve can be soldered or welded to the surrounding system, the actuator or its magnets are easy to replace without taking the valve out of service, and the external portion of the actuator can even function like a key and disconnect from the valve body when not in use.
Applications
Potential applications are innumerable. At the forefront today, we think of the complete elimination of fugitive emissions – zero – zero ppm – where not even a static seal is required anymore, if one isn’t wanted. This valve and the systems that employ it can be hermetically sealed. Lethal Service valves will be another critical application of the technology, and life-threatening leaks can be completely eliminated because the new type of hermetically sealed magnetic valve has no leakage paths.
Steam valves are another obvious application, as this new technology can support high temperatures and steam leaks are notoriously dangerous and wasteful. The valve can enable arbitrarily high levels of reliability in an overall valve system or network of valves – higher reliability than any other approach out there, including bellows, whose welded seam fatigues over time.
Pressure Testing.
AlNiCo Magnet.
Corroded Neodymium Magnets from Wave Energy Machine.
Long-term applications likely include semiconductor manufacturing and nuclear power. Marine and other harsh environments, or environments sensitive to contamination, such as food / pharmaceutical processing and medical systems are also strong potential applications. The valves can survive being run through an autoclave, in fact. Water, wastewater and even residential applications may well emerge, due to the lowered maintenance and zero leakage. Oil and gas pipelines stand to benefit twofold from the technology because it is both leakproof and tamper-resistant.
The actuator can be removed once the valve is set, and only authorized personnel will be able to access it, like a key. Two pipelines in the same right-of-way could be keyed differently to avoid confusion / mistaken actuation.
About the Author
Ned Davis is the Chief Innovation Officer at Plexis Engineering and holds a PhD, MS, BS in Mechanical Engineering & Masters in Electrical Engineering all from Johns Hopkins University. With 20+ years of engineering and engineering management experience, he has been working on Magnetic Valves in particular for 7 years. He started at Westinghouse and then Northrop Grumman, which provided him with extensive experience with naval & marine machinery, and avionics, harsh operating environments, etc. His hobbies include woodworking, metal-working, cooking, and swimming in the ocean.