Neles™ Q-Disc™ flow balancing trim for butterfly valves

Taking a closer look at dynamic torque

Dynamic torque is a challenge that all rotary valves, especially butterfly valves, face when in active flow control service. However, it is an aspect that is not as often taken into consideration when designing valve solutions and selecting the right configurations. While the requirements brought along by static torque are well addressed, we find that design considerations addressing dynamic torque are often an afterthought. For Valmet's flow control business line, it was a consideration that was at the core of the design process.

Dynamic torque is the flow-induced pressure torque placed on the valve in service. It is a direct result of the operating environment in which a valve is placed. Depending on the flow direction, valve travel and valve design, dynamic torque may even cause the valve to open or close. Rotary valves in throttling service may experience high torques, especially on larger valve openings. Valmet is seeking patent protection for the innovations that the new Q-disc is bringing to the table when it comes to tackling the effects of dynamic torque in butterfly valve applications.

Selection and sizing for optimal performance

Dynamic torque is also a key factor that has an effect on actuator sizing as a part of the valve assembly. Actuators may easily end up being undersized if only taking static torque into consideration. Also, when playing with high safety margins, actuators may end up oversized. Our Neles Nelprof™ sizing software takes dynamic torque into consideration and recommends the correct actuator automatically. Nelprof has all the different actuator characteristics inside, so sizing is accurate for all actuator types.

By taking dynamic torque into careful consideration and making the correct valve-actuator configuration choices, process efficiency and performance can be optimized. The Q-disc as a part of the valve assembly can deliver potential cost reductions and improvements in efficiency. A stable flow with minimized restrictions to capacity means even output and quality as well as reduced mechanical stress on valves.

Designed to improve performance

The Q-disc can have a positive effect on the dynamic torque coefficient of a butterfly valve. When looking at and measuring dynamic torque, we need to look at differential pressure and the valve size, or in the case of butterfly valves the size of the valve disc in particular. As dynamic torque is a result of the pressures created by the flow of media through the valves, things like disc geometry and shaft offsets come into play. The effects of the Q-disc’s integrated flow balancing trim on a triple offset butterfly valve can clearly be seen in the curve shown here.

The modular design of our latest range of versatile butterfly valves means that the Q-disc can easily be incorporated into any and all valve configurations. They have been designed by pressure class and valve size to ensure you always find the perfect fit. Speaking of fit, the Q-disc fits neatly inside the valve, requiring no deviations in terms of regular installation or maintenance procedures.

The benefits of an integrated trim solution

There is no separate external trim plate and no fasteners between the trim and disc. The disc and trim form an integrated piece with a rigid connection. There is a patent pending on this innovation. This solution has been found to work particularly well with bigger opening ranges. The Q-disc has excellent relative flow capacity compared to traditional flow balancing trims, and flow characteristics that are very similar to standard discs.

The Q-disc has an excellent relative flow capacity compared to traditional flow balancing trims.

And much like the other perforated integrated trims that carry the Q-moniker in the Neles product brand range, the Q-disc also acts to lower noise and cavitation. It has a positive effect on the valve choking factor (FL) and can be particularly helpful in reducing aerodynamic noise to some extent. All in all, the Q-disc is an innovation that was born out of the need and desire to improve process stability and ensure long-lasting performance and reliability. It is literally helping take some of the pressure off the shoulders of the butterfly valve’s disc and shaft.

The Q-disc seamlessly integrates the perforated trim plate with the disc.

Simulation-driven development process

The key to a relatively fast journey from idea to market has been the efficient utilization of simulations in the design and proof of concept phases. As a part of the process, tens of initial designs were iterated and the final design was selected to best accommodate the modular design and overall performance. After considerable testing and verification, this winning design is now seeing the light of day as a part of the first pilot cases in full operation. 

So many factors had to be considered before we had a final prototype in hand; dynamic torque, flow capacity, cavitation, noise, compressible flow, etc. The computational fluid dynamics analysis shows that performance figures are as expected. The structural analysis shows the needed strength and reliability of performance.

The end result – an innovation that delivers value

For us data simulations are the backbones of efficient innovation and design processes. The final verification of performance obviously still comes from stringent testing and piloting procedures. We are happy and convinced with the new Q-disc we are bringing to market. It is bringing tangible performance- and reliability-related benefits to our customers in a package that is designed to be easy to assemble, install, service and maintain.  

Dynamic torque & dynamic torque coefficient
Valve dynamic torque (M_d), which tends to close or open the valve depending on the type of valve, is caused by asymmetric pressure distribution on the surface of the throttling element, in this case the disc. The dimensionless dynamic torque coefficient (C_d) is a value determined experimentally using laboratory measurements.

Read also our blog Q-disc™ – Born to perform under pressure here.