Extending Operational Life and Ensuring a Tight Seal

The 3-piece O-ring groove created by the valve petals in the closed position as a solution to survive high-cycle fatigue & wear

The Shutter Valve™ employs a valve mechanism unlike any other design currently used for process control. Unlike the plug and seat combination of the globe valve, or the disc and seat configuration of a butterfly valve, the Shutter Valve has 3 precisely machined, interlocking petals that are capable of ANSI Class IV, Class V, or Class VI bubble-tight shutoff, depending upon the application.

Challenge
The 3 petals that function as the throttling mechanism in the Shutter Valve are essentially high-strength, robust metal blades that pivot about a hinge pin, into (or away from) the central opening of the valve, similar to the motion of scissors. The petals are driven by a rugged and efficient ring gear, which enables the Shutter Valve to operate with minimal torque.

Clarke Valve™ engineers needed to devise a method for creating a tight seal on the upstream and downstream faces of the valve petals, while avoiding erosion, pitting, or tearing of any seals or gaskets during operation.

Solution
After extensive testing in Clarke Valve’s R&D facility, as well as with customers in the real world, our engineers identified a design solution that would protect the inner diameter O-ring seal surrounding the central aperture of the Shutter Valve from particle impacts or fluid erosion, while still achieving a tight shutoff.

Figure 1: This side-by-side view illustrates the placement of the interior diameter O-ring in the body of the Shutter Valve. In the left panel, the groove (red arrow) that is machined into each half of the valve body is visible, around the central port. In the right panel, the O-ring has been placed into the groove. There is a corresponding groove and O-ring on each of the two halves of the valve body, resulting in a tight seal during shutoff on the upstream and downstream sides of the valve petals.

 

The axial face of each of the 3 petals is precisely machined to incorporate a curved arc-circle geometry. This approach benefits the Shutter Valve in 2 ways:

  1. The arc-circle of the petal prevents a shearing motion across the face of the O-ring by avoiding any pinch points between 2 metal surfaces: the O-ring only comes into contact with any of the valve petals during the full closed position.
  2. The lip of the arc-circle on all 3 petals presses tightly against the O-ring in the fully closed position, compressing it against the edge of the valve port and the groove where the O-ring sits in the valve body and cover, effectively creating the second half of the O-ring groove.
Figure 2: This rendering shows the orientation of the 2 interior O-rings (shown here in red), relative to the 3 petals and ring gear of the Shutter Valve, as the petals move from open to closed. In the first image (left), the valve mechanism is dissected, showing the 2 O-rings which are seated in matching grooves on both halves of the valve body. The valve body has been removed for this illustration, and the flow of process fluids goes straight through the port in the center of these O-rings. In the second image (center), only 1 of the O-rings is completely visible. The O-ring on the posterior of the valve mechanism is mostly obscured by the 3 open petals of the valve. In the third image (right), the valve aperture is closed, illustrating the tight fit of the O-ring against the concave circle formed by the axial faces of the 3 petals.

 

Similar to the seals in the bonnet and valve body, Clarke Valve made a design decision to use standard, off-the-shelf sizes for the O-ring surrounding the valve port. While the arc-circle design helps the O-ring to survive high cycle fatigue and wear, the use of standard parts will ensure that any service or replacements of the soft goods in the Shutter Valve is cost-effective, and immediately available in case of emergency, for the customer.

Figure 3: Another view of the placement of the interior O-ring around the valve port is shown above. When the three petals of the valve are closed (see Figure 2), they press tightly against the O-ring, compressing it into the groove around the valve port where it is seated. The white, arc-shaped element visible is the PTFE bearing, which the ring gear glides over, as it rotates. Finally, between the machined interior of the valve body and the exterior bolt-holes you can observe the outer O-ring that forms the pressure boundary of the Shutter Valve, which will be discussed in a future blog post. Similar to the interior O-ring, Clarke Valve uses off-the-shelf O-rings to make maintenance convenient and cost-effective for the end user.

 

Results
By using the arc-circle design, Clarke Valve has extended the life of the interior diameter O-ring in each Shutter Valve, while ensuring a tight seal when the 3 petals are in the fully closed position. Clarke Valve engineers have conducted 360,000 test cycles on a valve to successfully demonstrate the extended life of the O-ring seal, while maintaining the tight shutoff that results from this design.

Customers therefore benefit from longer periods between maintenance and greater overall uptime, while having total confidence in tight closure at ANSI Class IV, Class V, and even Class VI bubble-tight leakage ratings.