The interlocking seal and rib combination as a safeguard against seat leakage, high cycle fatigue, and wear

The Shutter Valve™ is a unique and innovative control valve design that signals a distinct departure from the globe, ball, butterfly, eccentric plug, and other variations used for shutoff and process control over the last 100 years.

The closest comparison to the Shutter Valve is the iris valve, which has seen limited market penetration as a control valve due to a few key flaws. 1) The angular elements of the iris are in constant contact with each other, even when the valve is fully open. This high amount of metal-to-metal component contact leads to high cycle fatigue and wear for the iris valve. 2) The sealing capability of the iris is limited, with limited leakage control along the adjacent boundaries of each component. 3) There is always a small opening at the center of the iris – even when the components of the iris are machined to very tight tolerances, gas or liquid at high pressure will leak through this pinhole opening, and prevent the iris valve from achieving Class IV, Class V, or Class VI leakage ratings.

Figure 1: Several examples of iris valve designs. In addition to the segmented aperture design shown here (typically constructed with metal) there is also a “diaphragm iris” valve which uses a single, dilating piece of pliable material to open and close the valve aperture.

 

Challenge
Clarke Valve™ set out to capitalize on the positive elements of an iris design—central flow stream, and a dynamically variable orifice—while addressing the seat leakage, high cycle fatigue, and wear that cannot be prevented for the iris valve, due to its inherent design flaws.

Solution
To address the wear and leakage of the iris valve, Clarke Valve has developed a control valve aperture comprised of 3 curved, interlocking petals.

 

Figure 2: The aperture of the Shutter Valve, comprised of 3 interlocking petals that pivot on a ring gear within the valve body. Here, one half of the valve body has been removed, and the Shutter Valve is in the fully open position.

 

First, we addressed the challenge of friction and wear by designing the Shutter Valve to prevent contact between the 3 petals during operation: the petals of the Shutter Valve are only in contact with each other when the valve is fully closed. As soon as the valve begins to open, the petals are moving away from each other to create a central aperture, without any of the sliding contact of the iris valve.

Animation of Shutter Valve opening and closing
Figure 3: This animation demonstrates the quarter-turn progression from open to throttling to closed for the Shutter Valve. The only time the three interlocking petals are in contact is at the point of full closure. As soon as the valve begins to open, the petals are separated, and pivot away from each other.

Next, we addressed the potential for leakage by designing each petal to feature a cavity along its top/outer surface that aligns with a protruding rib on the lower/inner surface of the adjacent petal. The result is that each valve has a male and female sealing component, which are machined to high precision. Extensive testing has enabled us to identify the optimal design ratio of rib height to width, and the corresponding dimensions for the sealing cavity for each valve trim and size. These design specifications address not only performance, but also manufacturability: we find the ideal seal-to-rib combination to achieve the highest working pressure class (ANSI 1500), while ensuring that each petal can be machined with maximum efficiency and minimal material waste.

The seal between these interlocking surfaces is further enhanced by the addition of soft material to the cavity on each petal, which can conform more tightly to the metal on the adjacent rib than a metal-to-metal connection would. For many applications, elastomer is used, which provides more flexibility and therefore, greater sealing ability, when compressed against the metal sealing rib on the adjacent petal. Through testing, we have found that a durometer between 60 and 80 is most effective, depending upon the application and the liquid or gases being handled by the valve.

Figure 4: The 3 petals of the Shutter Valve are shown in a throttling position (left), illustrating the manner in which the valve aperture is controlled by the petals pivoting in unison. On the right, 1 petal has been removed, providing a direct view of the interlocking seat-and-rib mechanism between the 2 remaining petals. The metal rib/male component on the inner curve of each petal fits precisely into the seat/female component (fitted with a PTFE seal, here) on the back of its neighboring petal. The removal of this petal also exposes 1 of the 2 black elastomer O-rings, which form a seal between the central valve port and the 3 petals, on both sides of the valve mechanism.

When a more durable material is required—for high velocity fluids with greater erosion potential, or corrosive fluids—we can equip the sealing surfaces of each petal with PTFE. In all cases, the elastomer or PTFE seals are designed to be recessed within the interlocking cavity, with minimal exposure to the fluids being controlled.

Figure 5: Individual valve petals shown from multiple angles, and with 2 types of sealing material. The left image illustrates the inner sealing surface of a petal, with the rib/male feature seen straight on. The seat/female feature in this petal is equipped with a white PTFE seal. Another angle (center) of the same petal shows the full length of the seat/female feature and white PTFE seal, as well as the arc-circle concavity on the petal’s face, which compresses the interior O-ring. A third view (right) shows a petal equipped with a black elastomer seal. The hole at the narrow end of each petal is for the stationary hinge pin, while the hole at the wide part of the petal is for the pivoting control arm.

The other leakage point of the iris valve—the central meeting point of the valve elements, which is never completely sealed—is addressed by the design of the interlocking notch at the end of each Shutter Valve petal. In a forthcoming post, we will outline the design of this critical feature of the valve.

Finally, as we will describe in greater detail elsewhere, there are 2 interior diameter O-rings that ensure a tight seal between the 3 petals and the ports on either side of the aperture. The O-ring sits in a groove that is machined into the valve body around the circumference of each port. The face of each petal is also machined to include an arc-circle concavity that compresses the O-ring when fully closed.

Results
The combination of all these elements allows the Shutter Valve to seal as tightly as any comparable control valve, and deliver a centralized flow stream, while minimizing the high cycle fatigue and wear that occur with designs like the iris valve. When appropriate torque is applied, the Shutter Valve can achieve ANSI Class V and Class VI bubble-tight shutoff using elastomer seals. For applications that require PTFE, we can achieve Class IV shutoff.

Furthermore, the deployment of 3 identically machined petals as the control and sealing mechanism also provides economies of scale, allowing Clarke Valve to reduce the cost of each Shutter Valve sold.