A Guide to Butterfly Valve Types and Double and Triple Offset Butterfly Valve Uses
Used to open and close, as well as regulate flow of liquid or gas, butterfly valves are composed of a circular disc and a rod that is connected to an actuator such as a handle. The disc, which rotates on a horizontal or vertical axis, should be around the same diameter as the connected pipe. Depending on how it is rotated, the disc is parallel to the pipe (valve is fully open) perpendicular to the pipe (valve is fully closed) or somewhere in between (the flow is being regulated). Butterfly valves are usually controlled manually.
How did butterfly valves get their name?
While some valves are named after their specific shape (globe valve, ball valve, needle valve), others are named after their motion or movement (slide valve, gate valve, pinch valve). Butterfly valves fall into the latter category — they are named after their movement — since the movements of the disc of a butterfly valve resemble that of the insect’s wings.
What are the uses of butterfly valves?
Butterfly valves are used to start, stop or regulate flow. This is done by rotating the built-in disc by 90 degrees. Lightweight and inexpensive, butterfly valves are corrosion resistant and can withstand extreme temperatures. This means that butterfly valves require little maintenance and rarely leak.
Just like ball valves, butterfly valves are quarter-turn valves. Unlike ball valves which are not suitable for regulating flow, however, butterfly valves can be opened and closed incrementally.
Where are butterfly valves located in systems?
Butterfly valves cannot be placed immediately next to certain system elements such as other valves, as well as elbows and pumps. Butterfly valves are normally assembled so that their stem sits vertically just under the actuator above. However, they can also be positioned horizontally if required.
Three main butterfly valve types
Butterfly valves come in different types, the most common being the zero offset butterfly valve, the double offset butterfly valve and the triple offset butterfly valve.
Zero offset butterfly valves
Also sometimes called rubber seated or concentric valves, zero offset butterfly valves do not have any offset by the stem. Instead, the seal is created at the meeting point of the valve’s seat and disc.
Zero offset butterfly valves have a low-pressure rating of up to 250 PSI and can operate in temperatures of up to 200 degrees Celsius.
Double offset butterfly valves
Double offset butterfly valves feature two offsets — one at the bore and the other at the disc seat/seal. These valves can withstand pressures of up to 1440 PSI and extreme temperatures of up to 650 degrees Celsius.
Triple offset butterfly valves
Engineered for a wide range of applications, triple offset butterfly valves feature two offsets in the centre and a third offset with cam action and right-angled sealing. Durable and frictionless, triple offset butterfly valves can withstand extreme pressures of up to 1,480 PSI and temperatures of up to 650 degrees Celsius.
Three main butterfly valve types
The unique features of butterfly valves make them a firm favourite in a number of industries including food processing, refineries and ship-building.
Low maintenance, simple design and durability are some of the key features that have made butterfly valves popular within the food processing industry. Butterfly valves are also bubble-tight, which means they do not let any bubbles through when pressurised on one side. Many butterfly valves on the market can be used in sanitary environments.
Refineries often utilise triple offset butterfly valves made from heavy-duty steel. Top performing butterfly valves are usually fire-safe and resistant to various substances.
Since most butterfly valves are resistant to salt water, they are often used in the shipbuilding industry. They are mainly utilised to stop all flow in piping systems and are valued for their compact size and ability to create water-tight seals.
Other valve types
Ball valves use pivoting bores to open and close the flow of liquid or gas. When the hole is parallel to the flow path, the flow is open. When it is perpendicular to the flow, on the other hand, the flow stops. Made from a range of materials from plastic to stainless steel, ball valves are usually controlled manually with a lever.
Non-return check valves
Also called retention valves, non-return check valves only let fluid flow in one direction. This stops liquid or gas from returning upstream of the valve. Non-return check valves typically feature two openings and a closing mechanism in between, which is kept open by fluid pressure. This mechanism also stops the fluid from flowing back in the other direction.
Pressure relief & safety valves
Both pressure relief valves and safety valves are used to discharge pressure within pressurised systems. Relief valves are the first port of call in cases of overpressurisation. In particular, they are usually installed to protect equipment from system failures. Meanwhile, safety valves are usually used as a last resort if all other valves fail to control pressure. As such, safety valves are engineered to release pressure immediately following a system failure.
Also called sluice valves, gate valves either stop or allow a flow of fluid (they act as a gate). As such, they are either fully open or fully closed and cannot be used to regulate flow stream. Gate valves are commonly used to close or open flow in water supply systems.
Butterfly valves feature a rotating disc that can either open or close the valve. The disc can be partially opened to regulate the flow. Gate valves, on the other hand, feature a drop gate that cannot be partially opened. As such, they can only be used to open or close a flow and not regulate it.
While butterfly valves have numerous advantages, they are not designed for operations that involve high differential pressure. This is because the valve’s disc responds to flow turbulence. Butterfly valves also have a poor sealing compared to some other valve types.
Butterfly valves are composed of four main parts. These include the body, stem, seat and disc.
- Body: While lugged butterfly valves feature protruding lugs that bolt to the pipe flanges, wafer butterfly valves do not feature protruding lugs. Instead, they are positioned between the pipe flanges.
- Stem: Butterfly valves come with either a one-piece stem or a two-piece stem design. Stems can be either in contact with the media (high performance valves) or protected from it.
- Seat: Usually made from polytetrafluoroethylene or reinforced polytetrafluoroethylene, seats are where the disc resists when the valve is closed. It is the seat that keeps the seals in butterfly valves from collapsing from impact stresses and friction.
- Disc: The closing and opening mechanism of butterfly valves. The disc is rotated 90 degrees to open or close the valve.
Butterfly valves feature different flow coefficients depending on their size. At the smaller end of the spectrum, 2-inch, 50-millimetre butterfly valves feature maximum flow velocity of 150 feet per second when the valve is fully open. In terms of middle-sized butterfly valves, a 10-inch, 250-millimetre valve features maximum flow velocity of 60 feet per second. Meanwhile, 12-inch, 300-millimetre butterfly valves come with maximum flow velocity of 50 feet per second. On the larger end of the scale, 20-inch, 500-millimetre butterfly valves feature maximum flow velocity of 50 feet per second.
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