Zero emissions stemless valve: A leak-free solution

Actuation Lab has developed an innovative stemless valve that Uses a magnetic coupling and torque amplification to eliminate emissions while maintaining high performance. This breakthrough could prevent millions of tons of greenhouse gas emissions and is ideal for hydrogen, toxic chemical and cryogenic applications.

By Dr Michael Dicker, CEng – CTO and Co-founder, Actuation Lab

A stemless valve is one which has no operating shaft passing through the valve body. This means stemless valves do not contain dynamic seals to atmosphere (e.g. packing), which are prone to wear and/or damage from eroded or corroded shafts, leading to fugitive emissions.

Why do we care about stem leakage?

Stemless valves are key to the safe operation of valves handling very aggressive or toxic fluids (e.g. chlorine), and are also used extensively for cryogenic applications where extremely low temperatures present a challenge to the effectiveness of stem seals.

Increasingly, stemless Valves are also being employed to provide a zero-emission solution where stem leakage has a global warming impact. Methane, the main component in natural gas, has 28 times the planet warming impact of carbon dioxide when it escapes to atmosphere. Even hydrogen, a clean burning fuel of the future, has an indirect impact 11 times worse than the equivalent amount of carbon dioxide. With hydrogen’s small molecular size resulting in it leaking much faster than natural gas, the climate impact of leaking valve stems will remain even if we phase out natural gas. Actuation Lab has performed studies that indicate around 93 million tons of carbon dioxide equivalent warming gas (methane) is emitted from leaking valve stems every year. Solving this stem leakage problem would have the same climate impact as removing all the cars and trucks from UK roads!

Leakage of gases like hydrogen, with its wide explosive limits (4-75%) is also a great motivator for the use of inherently leak free stemless valves. With many developers of hydrogen systems exploring containerised solutions, it takes only a small leak to trigger gas alarms in these confined spaces, leading to costly shutdowns (Figure 1). Additional financial benefits to adopting stemless valves include eliminating or reducing the cost of lost product, leakage detection and repair.

With these benefits, we might ask the question…

Why aren’t all valves stemless?

When we actually think about it, a lot of valves are stemless, for example the ubiquitous solenoid valve, which imparts force electromagnetically through the wall of the valve to operate. However, like all stemless valves, there are compromises. For solenoid valves there is a limit to the size/pressure this solution can handle, and/or a reliance on pilot pressure to operate.

For larger valves, replacing the dynamic stem seals with a metallic flexible bellows presents a solution. However, bellows are large and cycle fatigue life limited (particularly at higher pressures). In addition, they are predominantly applied to linear operating valves, designs that have just a fraction of the flow capacity of other equivalently sized valves.

Stemless axial flow designs also exist. These are pressure balanced, and actuated either hydraulically, electromagnetically (solenoid style) or with an electric motor embedded within the pressure boundary. While these designs improve the flow capacity compared to a bellows valves, flow still falls far short of something like a ball valve. In addition, concerns persist about the maintainability of solutions that embed actuators in the heart of the valve.

For uncompromised flow capacity, magnetically actuated ball valves have been developed. However, to allow the magnets to economically operate the valve, their input torque must be amplified through a gearbox placed inside the pressure envelope of the valve. As well as concerns this raises around maintainability, this can inhibit operating speed and the ability to implement spring-based failsafe actuation.

Ultimately, these existing solutions all contain weaknesses that increase their costs and severely limit their applicability. Is there a solution without compromise?

The Dragonfly valve by Actuation Lab

The Dragonfly valve is a stemless quarter-turn actuated non-contact (eccentric) ball valve, operated by a magnetic coupling. The concept of operating valves with magnetic couplings, like those commonly employed on pumps, is not new. In fact, the first patents for magnetically operated valves date back to the 1940s, yet magnetically actuated valves have had limited impact to date. One reason for this is that despite magnet strength increasing ten-fold since these first magnetic valve investigations, magnetic couplings still lack the torque to directly operate all but the smallest low-pressure valves, without the use of impractically large and expensive magnets. This is where the Dragonfly valve mechanism comes in. The patented Dragonfly valve mechanism amplifies the input torque from the magnetic coupling to open the valve. However, unlike using gears to amplify torque, the Dragonfly torque amplification is not constant (Figure 2).

The mechanism only produces the greatest amplification (10x) when the valve is near closed, corresponding to where there is the greatest torque demand from ball to seat friction and differential pressure. Once the valve cracks open, differential pressure reduces and the eccentric, non-contact ball cams out of the seat, reducing the operating torque demand at the same time as the amplification from the mechanism begins to drop. As the valve moves towards open, this amplification drops further, even falling below one and amplifying motion instead. This allows the valve to be opened quickly with just 90 degrees of input rotation, making the valve compatible with all quarter-turn actuators, including those that are spring return. The Dragonfly can also be supplied with our ‘Dragon Whisperer’ flow trims, to make it suitable for modulating control applications.

How do we achieve this non-linear torque amplification?

Our aim for the Dragonfly valve was to achieve the torque performance required to make magnets work, with the simplest, cheapest and most robust mechanism possible. The Dragonfly mechanism adds only a single additional moving component into the valve, compared to a traditional eccentric ball valve, a part we call the Dragonfly “tail”. Torque is input to the ball through the tail, rather than the trunnions (Figure 3).

Is it really without compromise?

As we know, there is no one valve that is right, or the best fit, for all applications. Equally, stem leakage isn’t a big problem on valves like manual isolation valves that only operate a handful of times in their life. The Dragonfly valve is a single-seated valve, and we are not targeting it at these types of applications. Instead, we are focusing on valves that operate regularly, either control valves or automated on-off valves, in applications where stem leaks cannot be tolerated. Although the mechanism is designed to be robust, we are initially looking to deploy into relatively clean service. These are compromises, but ones we think are acceptable.

Perhaps the biggest compromise that you might be expecting with the Dragonfly valve is price. While we can make some strong arguments for the total cost of ownership improvements a stemless valve can provide, purchase price is ultimately still a big driving factor in valve selection. A magnetic coupling is more expensive than a mechanical stem, but when considering the Dragonfly valve as an actuated package or as a ball valve that can replace a much larger globe valve, the Dragonfly valve can be very competitive.

Dragonfly mechanism not only enables the use of magnetic couplings, but also means the actuator can be 10x smaller. This can represent a significant cost saving or allow electrification where previously a costly pneumatic supply system would be required. For example, a lower torque, fast electric actuator can now be used, where previously a pneumatic actuator would be required for a control application. Similarly, the high flow capacity of the Dragonfly valve’s eccentric ball design means that a much smaller valve can be used to meet the same flow requirements. For example, where previously a larger globe valve would have been used because of the need to employ a bellows seal, ensuring toxic chemicals stay in the pipe, a smaller and thus cheaper Dragonfly valve can now be employed.

Dragonfly valve – State of development

The Dragonfly valve has been in development for the last 2 years, with a focus on development for gaseous hydrogen applications, with funding from the UK Department for Energy Security and Net Zero. A range of valve sizes have been produced from 3/8 NPS (DN 10) to 4 NPS (DN 100), and pressures up to class 2500 (PN 400). Valves have undergone witnessed testing with Score Group and LRQA. The valve is actively being trialled with hydrogen (Figure 4) and ammonia, with natural gas trials to begin in 2025. A cryogenic version of the Dragonfly valve is also in development.

The Dragonfly valve is officially launching at Valve World Düsseldorf 2024, come and find us in Hall 1, Stand E32 (next to the BVAA stand).