Butterfly valves are part of a class of quarter-turn valves used to regulate fluid media flow. They function similarly with ball valves, notwithstanding they differ in effectiveness and performance. Butterfly valves are made up of an elongated disc connected to a rod. The rod’s rotation determines the closing and opening of the valve.
Because of their lightweight and low cost, their small area of installation, and their larger designs, butterfly valves can be found in many applications across different industries. The valves can operate by hand using gears and handles or through automated actuators. We’ve discussed more of them below.
Where can butterfly valves be used?
Butterfly valves serve a wide range of uses in the water supply and wastewater treatment as well as gas supply and protection from fire as well as in the oil and chemical industries, as well as in the power industry, in fuel management systems, etc. One of the benefits of this kind of valve includes the simplicity of construction, not taking up a lot of space, and the low weight and cost savings compared to various valve models.
How Butterfly Valves Function
Butterfly valves have a body or housing and stem, seal, and a disc of a simple design. The disc lies perpendicularly towards the direction of flow in a closed state and is secured with the valve’s seat. The disc is typically placed in the middle of the stem, as is the pipe connected to it, while an o-ring seals off the stem attached to a handle or actuator.
Figure 2: Actuator/handle (A), Stem (B), Stem O-ring (C), Seal (D), Disc (E), Valve body (F).
If the actuator or handle turns the stem 90 °, the disc shifts away from the valve’s seat, it is then positioned in a line in a parallel position to the flow. The stem’s rotation partially permits fluid flow to become throttled or proportional.
When butterfly valves are utilized to modulate services, they can be either linear or possess characteristics of an equal proportion. The former signifies that equal increments in valve travel result in an equal percentage increase in flow rate.
Parts of the butterfly valve
Below are the most critical parts for a butterfly valve.
The valve’s body is inserted within the pipes flanges. The most commonly used end connections are double lug, flanged, and wafer.
The disc is connected to the valve’s body, which functions as a gate, which prevents or throttles flow. It is equivalent to an entrance gate in gate valves or a ball within the ball valve. The disc is usually bored to accept the shaft or stem. There are numerous designs and orientations, and the material increases the flow, seal, or operating torque. For example, the Hawle double eccentric disc 9881k has been specifically designed to minimize wear of seals and “scuffing” and the operating torque requirement.
The valve’s internal lining is a durable elastomer (or metal seal) that keeps the disc with the valve closed to ensure total shutoff. This series’ stainless-steel filled with welds and micro-finished body seat is guaranteed to protect against erosion and corrosion of the face of the seat. With this type of seat design, it’s possible to make this valve tight to conform to EN12266 -A specifications.
The valve shaft, which is often known as”the stem,” is the element that connects the disc to the mechanism that actuates it and transfers the torque through it.
Seals are found at multiple points within the valve to ensure a secure seal during operation or separate the process media and valve components, resulting in greater flexibility and a cost-effective design.
Butterfly Valves Types
Butterfly valves can be classified based on the disc closure’s design, the actuation method, and the connection design. Below is a brief description.
Design for Disc Closure
Within this category, there are two types of valves: concentric and eccentric. The classification is based on the position of the stem relative to the disc and the angle at which the disc shuts.
The concentric valve is the seat is within the circumference of the valve’s body, and the stem is inserted into the centerline of the disc. It is a zero offset valve, in which the flexibility of the seat rubber determines the seal’s performance as the valve gets shut. These valves are typically employed in low-pressure applications.
Butterfly valve Seat Construction
The stopping of flow is achieved by sealing the valve disk against a seat situated on the inner diameter inside the valve’s body. Many Butterfly valves feature an elastomeric seating area against which discs seal. Some Butterfly valves come with an arrangement for a seal ring which uses a clamp-ring and backing-ring with serrated edged rubber rings. This prevents the expansion of O-rings.
In the beginning, a disk of metal was used to close against a seat of metal. This design did not offer an impermeable closure; however, it was adequate in specific applications (i.e., distribution lines for water).
A butterfly valve is attached to the piping system in a variety of ways. There are three typical valve designs based on the connection style. They are lug type; one type is called a wafer, the other is a flange connection. The wafer design is the most cost-effective as well as it’s specifically designed to provide efficient sealing against bi-directional pressure differences and backflows.
The lug design has threaded inserts outside of that valve’s body. This permits the disconnecting of the opposite side to allow dead-end services. These valves are typically made for use in low-pressure applications and carry the load of the pipe within the body of the valve.