Valve World Magazine November 2024 | Page 35

High-performance butterfly valves are common across a wide range of chemical and petrochemical processes . They may be manual or automated , but their favorable price point and significantly reduced footprint make them an excellent solution for equipment isolation applications . While there are many types of butterfly valves available , there are significant differences in their internal design , which directly impact their sealing performance and long-term reliability . This article focuses on the key design features to help users evaluate the best alternative for their critical on / off valve applications .

Applications suited for butterfly valves

While a high-performance butterfly valve may be used in a variety of situations , they are best suited for equipment isolation and on / off applications requiring bubble-tight , zeroleakage shutoff . These valves are generally less expensive than plug or ball valves , especially as line sizes get larger . They also take up far less space when installed , allowing them to fit in tight piping configurations , where space may be limited . While butterfly valves can be utilized for flow control , their control range is somewhat narrow , so the requirements of the application must be carefully evaluated before using these valves in throttling service . There are a multitude of high-performance butterfly valve body and sealing designs , but the overall performance and long-term reliability varies significantly among models . When choosing a valve , it is important to

BUTTERFLY VALVES

Choosing butterfly valves for complete shutoff

Advanced valve disc and seat designs allow some highperformance butterfly valves to maintain superior sealing over a significantly extended service life .

Karin Pharr , Emerson

understand the differences to select the right valve for a particular application and budget .

Valve sealing and packing design alternatives

When evaluating a high-performance butterfly valve , users should start with the disc and seat design . Some butterfly valves wedge the disc into a soft seat and rely on process pressure to provide reliable shutoff . Such valve designs only work with pressure on a particular side of the valve and will perform poorly in bi-directional applications . Other valves utilize seat designs that continuously wear as the valve moves , creating leakage after a short time in service , and eventually causing premature failure of the seat . Better valve designs utilize a double offset design that allows the disc to wedge tightly into the seat at the end of travel , yet lift quickly off the seat after only a few degrees of travel to limit wear ( see Figure 1 ). Such designs offer zero-leakage , bubble-tight sealing due to the double offset camming motion , and they can maintain that level of performance over an extended life since the seat is only engaged in the final degree of movement . The double cam design also operates independent of system pressure , so the valve provides zero leakage regardless of system pressure . It can also operate with pressure on either side of the disc , and it can even seal when installed on the end of a pipe with one side exposed to atmosphere . A double offset design does offer advantages , but the valve life is significantly increased when that design is combined with a self-adjusting seal composed of very long wear materials , backing

Double Offset

Seat backing ring

Seat wire

Seat retainer Seat ( see table below for materials ) ring

Seat retainer ring gasket

Figure 1 : Long life high-performance valves , like Emerson ’ s Keystone™ K-LOK ® Series 38 , utilize a double offset design paired with a heavy-duty polymer seat , backing rings , and internal wire wraps to allow the seal to adjust as the disc cams into it . π www . valve-world . net Valve World November 2024

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