07 Dec How to Select Parts for Rubber Seated Butterfly Valve
For the last several decades, butterfly valve technology has become increasingly common. Butterfly valves are now used in the processes of virtually every chemical plant. What started off as an ideal quarter-turn function for water applications became a versatile valve made from various materials that are appropriate for most kinds of fluids and media.
Rubber seated butterfly valves boast a tight shut-off and are tested to meet specific industry standards. With testing, we can be sure that they will serve reliably for safe and smooth operation.
For quality control and planning purposes, it’s useful to understand all the parts involved with a rubber seated butterfly valve. In this guide, we’ll go over what is included with a butterfly valve installed and the role each part has.
What is a Rubber Seated Butterfly Valve?
A butterfly valve regulates fluid movement with a rotating disc that securely closes off the flow. This valve is like a ball valve with its quick shut-off functionality. What differentiates this valve from a ball valve is that its disc is always present in the flow to induce a pressure drop.
Rotation turns the disc either perpendicular or parallel to the media flow. The advantage of butterfly valves compared to ball valves is that they are less expensive, and because they are lighter weight they require less support.
Butterfly valve design varies from zero-offset valves to triple offset (high performance) valves. A zero-offset valve is known by a few names: “concentric,” “resilient seated butterfly valve”, or “rubber seated butterfly valve.”
AWWA valves are an example of how rubber seated butterfly valves are ideal in function. AWWA parts have to meet specific standards and rubber seated butterfly valves work well because they are leak-proof, corrosion-resistant, and low-maintenance.
Choosing Rubber Seated Butterfly Valve Components
Each part serves a significant purpose in the unique design of a rubber seated valve. The butterfly valve dimensions must be precisely suited for various industry standards and functions. Sound operation and reliable sealing are needed for applications in the following scenarios:
- Pharmaceutical industry
- Chemical processes
- Food industry
- Water and wastewater
- Fire protection systems
- Gas supply likes
- Low-pressure steam
The centric-design of the standard zero-offset butterfly valve has all the pieces in the center. The valve body has no offset, nor is there a stem packing adjustment. The disc rotates a full 360º around the central axis with a secure seal made between the disc edge and the rubber seat at the stem.
The rubber seat that covers the body prohibits the valve from coming into contact with the materials that flow through the pipe. The following parts work together to ensure that the media remains untouched.
- Dust Seal (Packing)
- Bushings or Bearings
To better understand how each part is involved, we’ll go over the different components of the rubber seated valve anatomy.
Butterfly Valve Body
You’ll find the valve body between the pipe flanges as it holds the valve components in place. The valve body material is metal and made from either carbon steel, stainless steel, titanium alloy, nickel alloy, or aluminum bronze. All but carbon stell are appropriate for corrosive environments.
The body for a butterfly control valve is typically either a lug type, a wafer type, or double flanged.
- Protruding lugs that have boltholes to match with those in the pipe flange.
- Allows dead-end service or downstream piping removal.
- Threaded bolts around the entire area make it a safer option.
- Offers end-of-line service.
- Weaker threads mean lower torque ratings
- Without protruding lugs and instead is sandwiched between the pipe flanges with flange bolts surrounding the body. Features two or more centering holes to help with installation.
- Does not transfer the weight of the piping system through the valve body directly.
- Lighter and cheaper.
- Wafer designs do not transfer the weight of the piping system directly through the valve body.
- Cannot be used as a pipe end.
- Double flanged
- Complete flanges on both ends to connect with the pipe flanges (flange face on both sides of the valve).
- Popular for large size valves.
Butterfly Valve Disc
The valve disc serves as the gate to start and stop fluid flow. It’s analogous to a ball in a ball valve. Discs are made from metals but can be coated with other materials (such as nylon or nickel). Such metals used are ductile iron, aluminum, or stainless steel.
The disk rotates one-quarter turn (or 90°) to open or close the butterfly valve. With precise design, the disc will align perfectly with the rubber seat to create an impermeable seal.
Butterfly Valve Stem
The kind of stem needed for an application depends on contact with fluids. For most resilient seated designs, the stem remains tucked away and protected from the fluid media. However, with high-performance valves, the stem does make contact with the fluid.
With stems, you may see either a one-piece shaft or a two-piece (split-stem) design. The stem is mounted on a vertical axis at the center of the disk connected to the actuator. A seal along the edge of the disk’s elastomer lining for a tight shut-off.
So when it comes to stems, a deciding factor is if it is going to be in contact with the media or not and are they strong enough to endure the amount of action the process entails.
In high-performance butterfly valves, the shutoff may be provided by an interference-fit seat design or a line-energized seat design, where the pressure in the pipeline is used to increase the interference between the seat and disk edge.
Butterfly Valve Seat
What makes the rubber seated valve different is its “soft” seat. These rubber rings (or “O” rings) are made from many different elastomers or polymers that secures the valve disc into place for an anti-leak seal. The rubber seated valve is also ideal for low-torque applications.
Teflon is the most common kind of seat material for both versatility, heat-resistance, and endurance. In addition to Teflon, we have EPDM, white EPDM, Buna N, Viton, Viton for Steam, Silicone, and Neoprene materials. Some seating is considered “food grade” such as those made of white EPT.
Rubber Seated Butterfly Valve Dimensions
Rubber seated valves come in different sizes to suit different applications. You may have already heard of an “8 butterfly valve” or a “12 butterfly valve”.
Our Reliant VF7 brand Teflon resilient seated butterfly valve comes in six sizing categories: 1 ½” – 14”, 1 ½” – 2 ½”, 3”, 4”-6”, 8”-14”, and 16”-24”. Butterfly control valves can be even larger than this – some are so big an adult could walk through its ring without bumping their head.
The individual parts are proportional to the size of each valve. For example, a centric valve (Teflon resilient seated butterfly) with a body of 8.19 inches would have a disc 1.54 inches tall, an outer ring 1.69 inches thick, a shaft end of 0.75 inches long, etc. The proportions for this design would be roughly the same incrementally as the valve size increases.
The Butterfly Valves & Controls product catalog includes all the specifications and manufacturer documentation with each product. There you will find detailed measurements, diagrams, and dimension information for all the valves we offer.
Contact Butterfly Valves & Controls Today
Butterfly Valves & Controls, Inc. is a premier supplier of quality butterfly control valves and related components. For over 25 years, we’ve carried only the best parts sourced from world-class manufacturers. We offer products with an extended service life with safe operations. If you are ever in any doubt about the longevity or quality of the rubber seated butterfly valves or parts in your processes, contact us right away. We’re here to answer any pressing questions so that you can rest assured that your operations are safe, reliable, and compliant.