Butterfly Valves

Butterfly VALVES

Butterfly Valves are Bi-Directional Quick Shut Off Valves and are available in Lug or Wafer or Double Flanged Type in Various material combinations for use in Residential and Commercial Buildings.

A butterfly valve is a quarter-turn rotational motion valve, which is used to stop, regulate, and start the flow. Butterfly valves are easy and fast to open. A 90-degree rotation of the handle provides a complete closure or opening of the valve. Large Butterfly valves are usually equipped with a so-called gearbox, where the handwheel by gears is connected to the stem. By this, the operation of the valve is simplified but at the expense of speed. Butterfly valves have a short circular body, a round disc, metal-to-metal or soft seats, top and bottom shaft bearings, and a stuffing box. The construction of a butterfly valve body varies. A commonly used design is the wafer type which fits between two flanges. Another type is the lug wafer design which is held in place between two flanges by bolts that join the two flanges and pass-through holes in the valve’s outer casing. Butterfly valves are also available with flanged, threaded and butt welding ends, but they are not used often.

These valves have many advantages over the gate, globe, plug, and ball valves, especially for large valve applications. Savings in weight, space, and cost are the most obvious advantages. The maintenance costs are usually low s there are a minimal number of moving parts and there are no pockets to trap fluids. These types of valves are especially well-suited for the handling of large flows of liquids or gases at relatively low pressures and for the handling of slurries or liquids with large amounts of suspended solids. They are built on the principle of a pipe damper. The flow control element is a disk of approximately the same diameter as the inside diameter of the adjoining pipe, which rotates on either a vertical or horizontal axis. When the disk lies parallel to the piping run, the valve is fully opened. The valve is shut when the disk approaches the perpendicular position. Intermediate positions, for throttling purposes, can be secured in place by handle-locking devices.

The stoppage of flow is accomplished by the valve disk sealing against a seat that is on the inside diameter periphery of the valve body. Many butterfly valves have an elastomeric seat against which the disk seals. Other butterfly valves have a seal ring arrangement which uses a clamp-ring and backing-ring on a serrated edge rubber ring. This design prevents extrusion of the O-rings. Typical services include; hot and cold water, HVAC, steam, compressed air, gas, and other general utility services.

Butterfly valve: working principle

 The construction of a butterfly valve is relatively simple, with the rotation of the valve disc controlling the fluid flow. In the closed position, the disc blocks the valve bore while in the open position, the disc is oriented perpendicular to the flow direction to allow flow. Butterfly valves generally provide bi-directional flow and shutoff capability. However, they are not full-bore, which renders them unsuitable for pigging or swabbing. The body material is ductile iron with an epoxy powder coat on both internal and external surfaces. The valves are typically operated by handwheels, gears, or actuators, or a combination thereof, according to the specific application requirement and technical specifications. We will be discussing the actuation methods later in the article.

Butterfly valve actuation

There are multiple ways to operate, or actuate, a butterfly valve – manual, semi-manual, or fully automatic.

Electric: Uses an electric actuator for controlling the valve with a 4-20mA control signal and are typically used for high precision regulation and time-sensitive application.
Pneumatic: Also used for high precision application and uses compressed air for actuation.

Hydraulic: Typically used for applications requiring large torques for opening and closing the valve, such as high pressure and high viscosity applications.

Manual: Manually operated butter valves make use of a handwheel, crank, or lever to operate the valve. Smaller manual valves are typically fitted with a lever. For larger sizes, handwheels are provided and are accompanied by a gearbox to transfer the torque with a high mechanical advantage. Another way of manual actuation is in use cases where the valve is buried underground without a manhole; in such applications, actuation is done with an extension spindle, adapter / square cap, and a corresponding T-key from the ground level.

TYPES OF BUTTERFLY VALVES

Lug Type

WAFER TYPE

FLANGE TYPE

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