The Dragonfly Valve – A New Stemless Alternative to Bellows Sealed Valves

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 the atmosphere (e.g. packing), which are prone to wear and/or damage from eroded or corroded shafts, leading to 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.

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. Additional financial benefits to adopting stemless valves include eliminating or reducing the cost of lost product, leakage detection and repair.

The use of metallic flexible bellows is a common solution where stem leakage cannot be tolerated. 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.

The Dragonfly Valve provides stemless operation without these compromises. The Dragonfly Valve is a high-flow capacity non-contact (eccentric) ball valve, operated by a magnetic coupling. Magnetic couplings, like those commonly applied on pumps, eliminate the opportunity for external leakage, no matter how many cycles the valve undergoes. The use of magnetic couplings is enabled by the Dragonfly Valve’s extremely low operating torque, just 1/10th of an equivalently sized ball valve. This 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.

The valve can be opened quickly with just 90 degrees of input rotation, making it compatible with all quarterturn actuators, including those that are spring return. The Dragonfly Valve can also be supplied with our ‘Dragon Whisperer’ flow trims, to make it suitable for modulating control applications.

The Dragonfly Valve has been in development for the last two years, with a focus on gaseous hydrogen applications, with funding from the UK’s 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). The valve is currently in industrial trials in the UK and mainland Europe, handling both hydrogen and ammonia. If you work in chemical processing, industrial gas, or related sectors and are dealing with fugitive emissions, sealing issues, or frequent valve servicing challenges, we’d love to help. Please get in touch to discuss how the Dragonfly Valve can support your plant’s performance or to arrange a trial.

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

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