Zero-Leak Valve Design
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 quarterturn 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 ,
Figure
2 : Torque amplification of the Dragonfly mechanism as a function of actuator input angle , 0 degrees corresponds to valve closed position .
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 ).
Figure 3 : Cross section of Dragonfly valve in open position
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
38 Valve World December 2024 www . valve-world . net