1. What is Butterfly Valve?
Butterfly valves are quarter-turn rotational motion valves used in pipelines to stop, regulate and start flow.
Butterfly valves, a 90° rotation of the handle that can be completely close or open the valve, are easy and fast to operate.
The main difference between butterfly valves as compared to other valves is the disc. The butterfly valve disc is always in the flow causing a pressure change for any position of the valve.
2. What are the types of Butterfly Valves?
Butterfly valves are usually made up of a short circular body, round discs, metal-to-metal or soft seats, top and bottom shaft bearings, and stuffing boxes.
There is two main types of Butterfly valve body, namely the Wafer type, and Lug Type. Wafer type is a commonly used design that fits between two flanges, while lug type is usually used in place between two flanges by bolts that join the two flanges.
Butterfly valves have few advantages when used in large valve applications as compared to the gate, globe, plug, and ball valve. Weight, space, and cost are the most obvious advantages, the maintenance cost is usually low as there are only a minimal number of moving parts and there is no pocket for fluids trap.
Butterfly valves are perfect when handling a large flow of liquids or gases at relatively low pressure. It's also suitable for handling slurries or liquid with a large number of suspended solids.
The designation of butterfly valves is based on the principle of pipe damper, with the flow control element that consists of a disk of nearly the same diameter as the inside diameter of the adjoining pipe, which axis rotates either vertically or horizontally.
Butterfly valves are fully opened when the disk lies parallel to the pipping and the valves are shut off when the disk approaches perpendicular positions. The butterfly valve can also be put into intermediate positions, for throttling purposes, and this action can be secured in place by using the handle-locking devices.
ANSI 150# Cast Iron Lug Type Butterfly Valve
3. Butterfly valve Seat Construction
Butterfly valve achieves stoppage of flow by using the valve disk sealing against a seat on the inside diameter periphery of the valve body.
Most Butterfly valves have an elastomeric seat against which the disk seals, while some Butterfly valves have a seal ring arrangement that uses a clamp-ring and backing-ring on a serrated edge rubber ring, it prevents extrusion of the O-rings.
4. Butterfly valve Body Construction
The body type for the Butterfly valve varies from the wafer type and the lug wafer design. The most commonly used type that installers choose is the lug wafer design, which is chosen in placement between two pipe flanges by bolts that join the two flanges and pass-through holes in the valve’s outer casing. Meanwhile, the wafer types are more economical when it comes to pricing, and are commonly used to fit between two pipeline flanges.
5. Seat Disk and Stem of a Butterfly valve
ANSI 150# Cast Iron Lug Type Butterfly Valve
The stem and disk for a Butterfly valve are two separate pieces, the disk is bored to receive the stem.
There are two common methods used when securing the disk to the stem so that the disk rotates as the stem is turned.
The first method, bolts or pins are used to bore through and secure the disk to the stem.
The second method involves boring the disk as before, then shaping the upper stem bore to fit a squared or hex-shaped stem, this allowed the disk to "float" and seek its center in the seat and accomplish uniform sealing where external stem fasteners are eliminated. This method of assembly is beneficial for covered disks and in corrosive applications.
The stem must be extended beyond the bottom of the disk and fit into a bushing on the bottom part of the valve body in order for the disk to be held in a proper position. These bushings must be resistant to the media that’s being handled or sealed to avoid the corrosive media from coming into contact with them.
Stem seals are achieved by packing in a conventional stuffing box or O-ring seals. Valve Manufacturers, in particular, those specializing in the handling of corrosive material usually place a steam seal inside the valve so that no material handled by the valve comes into contact with the valve stem. In cases where a stuffing box or external O-ring is applied, the fluid passing through the valve will have contact with the valve stem.
6. Applications of Butterfly Valves?
Butterfly valves are used in various types of fluids applications due to the great performance that can be achieved in slurry applications.
The following are some applications of Butterfly valves:
Low maintenance cost, high durability, and simplistic design are key features considered for regulated fluid flow in any pipping system.
The white seat is the preferred seat when it comes to certified food grade standards used for the food processing sector. Although standard resilient seated valves are not 3A approved, there are still many on the market that keep sanitary connections inside and outside.
A butterfly valve is commonly used in refineries as well, these would typically require the “high end” High-Performance valve with Steel Bodies, or Triple Offset design that adhere to “Fire Safe” and bubble tight. While for water applications resiliently seated versions are usually preferred.
Shut Off Valves
A butterfly valve is often the preferred choice as a general shut-off valve for sizes between 1.5 inches – 148 inches. Their simple design enables them to use up less space and lighter weight as compared to other types of valves.
Butterfly valves provide a tighter seal than a gate valve or globe valve and are bubble tight. This is most important when attempting to stop the fluid flow as it prevents any form of fluid from passing through the pipe when closed.
Butterfly valves are commonly used in ships vessel where ABS-approved materials are required due to their high durability in saltwater. This type of valve consistently creates a water-tight shutoff in the piping system of a shipping vessel where it prevents any flow in the pipe. Their compact design also enables them to be used in tight spaces that are common aboard the ship.
Butterfly valves can also be used for “jack up” rigs, ballast systems, ship side, and many more other applications. Fire Safe approved valves are also key requirements for many applications.
Advantages of Butterfly valves
Compact design requires considerably less space, compared to other valves
Light in weight
Quick operation requires less time to open or close
Available in very large sizes
Low-pressure drop and high-pressure recovery
Disadvantages of Butterfly valves
Throttling service is limited to low differential pressure
Cavitation and choked flow are two potential concerns
Disc movement is unguided and affected by flow turbulence
HOW TO INSTALL A BUTTERFLY VALVE
To avoid limiting disc movement or damage to the disc or seat, assure that the pipeline and flange faces are clean from any foreign material such as metal filings, pipe scale, welding slag, welding rods, etc.
Because they extend to both sides of the valve, resilient seated valves do not require gaskets.
Align the pipe-work and spread the flanges far apart enough to allow the valve body to be easily inserted between the flanges without coming into contact with the pipe flanges.
Make sure that the valve has been set to about 10% open in order to avoid getting jammed in the fully seated position.
Insert the valve between the flanges as illustrated, to avoid damages being made on the seat faces. Always lift the valve through the locating holes or with a nylon sling on the neck or the body. Avoid lifting the valve by the actuator or operator mounted on the valve.
Place the valve between the flanges, center it, hand-tighten the bolts after insertion. Carefully open the disc, making sure that the disc does not make contact on the inside of the adjacent pipes.
Close the valve disc slowly and carefully to ensure the disc edge clearance from the adjacent pipe flange.
Fully open the disc and tighten all flange bolts as shown. Repeat a full close to the full open rotation of the disc to ensure proper clearances.