Reliable for Over One Million Mechanical Cycles

The design considerations of the ring gear to survive high cycle fatigue and wear

As described elsewhere, Clarke Valve™ engineers identified a highly efficient means to provide precision process control and tight shutoff for the Shutter Valve™, through the use of a ring gear and control arms to drive the 3 petals and compress the proprietary interlocking seals of the valve mechanism.

Challenge
The centralized flow stream and other design features of the Shutter Valve significantly reduce cavitation, turbulence, and other forces that can lead to fluid erosion of the valve body and downstream connections.

To fully capitalize on this potential for longer operational life, the Shutter Valve requires the ring gear itself to be sufficiently durable to complete hundreds of thousands (or even millions) of mechanical cycles without binding or otherwise breaking down.

Solution
Ring gears are well known to be rugged and dependable. Although Clarke Valve can manufacture the ring gear using different alloys to meet customer specifications, we most commonly form the ring gear out of 17-4 stainless steel. This is due to its inherent resistance to corrosion, its machinability, and the high levels of hardness that can be achieved with heat treating. Similar considerations led us to choose 316 stainless steel as the standard material for the Shutter Valve body and bonnet, with other alloys available to suit the customer’s application.

The configuration and the tolerances of the gearing in the Shutter Valve are so precise and well designed that the mechanism essentially runs dry, with little or no lubrication required for sustained operation. Clarke Valve works closely with our partners at Tracey Gear to optimize the efficiency of the ring gear and pinion gear. The beveled teeth of both gears and the precisely calculated mounting distances enable the two gears to mesh and operate for millions of cycles with minimal wear.

Shutter Valve ring gear teeth close up
Figure 1: The gearing of the Shutter Valve has been the focus of much testing and analysis. Here, the current design of the ring gear teeth shows the precise dimensions that Clarke Valve has identified for maximum efficiency and durability of our quarter-turn control valve.

Over time, all of the components of the Shutter Valve have evolved, including the design of the control arms and the design of the ring gear itself. The original ring gear was more of a true ring, with a thin circumference wall, and little or no material providing support within the interior of the ring. Although this design had the benefit of lighter weight, we observed that the considerable amount of machining required to create such a ring created a high amount of stress in the metal, and the ring was consequently prone to deformation. For a time, we machined support brackets with Teflon inserts into the valve body, to help the ring gear maintain its circumference.

Ring gear design evolution
Figure 2: This example of the Shutter Valve shows an earlier design of the ring gear. The gear itself is a true ring, with a hollow inner circumference. Three white PTFE “pills” sit in brackets to guide and stabilize the movement of the ring gear. The linkage arms shown in this model of the Shutter Valve have been replaced by the integral control arms that are now used. This design update has reduced the number of parts in the valve mechanism from 22 parts to 7 parts, simplifying assembly and increasing durability.

 

Eventually, we identified the “hub” design, employed in all of our new Shutter Valve iterations, as a solution to the problem of stress relief. The more robust hub design reduces the amount of machining required, when compared to the earlier design, and confers greater rigidity on the ring gear mechanism. Through testing, the hub design itself has also gone through some iterations. Below, left, is a version that has a slight ridge around the top interior of the ring gear circumference, with insertion points for the pins that drive the control arms. On the right side of the image below, you can see that we have made the interior ridge wider, and moved it to the bottom of the interior circumference, i.e. the surface that rides on a bearing in the valve body.

Ring gear design updates
Figure 3: Two more examples of the ring gear design evolution. The design on the left shows insertion points for control arms on the top of the ring; i.e., on the same side of the ring as the gear teeth. The design on the right is more current, with a thicker interior ridge and the insertion points moving to the bottom side of the gear; i.e., the opposite side of the gear teeth.

By placing the insertion points for the control arms on the bottom of the ring gear/hub, this allows for increased ease of initial assembly and rebuilding:

  • The hub drops into the appropriate groove in the valve body
  • The integral arms drop into the hub
  • The petals drop onto the arms

The hub glides on a bearing in the valve body, and is machined to fit into a precise groove around the central aperture of the valve, adding yet another level of stability and durability to the mechanism.

Results
In testing, the ring and pinion gear have successfully completed over one million cycles without binding or freezing. To date, we have also not had any reported failures of the ring gear in our installed base.

As the evolution of the hub design shows, we are continuously refining every aspect of the Shutter Valve. By using bench testing and finite element analysis, Clarke Valve will constantly work to extract still more value from the already dependable Shutter Valve design, for the benefit of our customers.