Butterfly Valves

Butterfly Valves

Butterfly Valves are of the quarter turn family and are so designed because a 90 degree turn of the operator fully opens or closes the valve. The position of the lever indicates whether they are wide open, partially open or fully closed. Some larger butterfly valves may have a hand wheel that operates through a gearing arrangement to operate the valve. This method is used especially where space limitation prevents use of a long handle. They are easily adapted to lever, manual, gear, electric or pneumatic operation.

The butterfly valve has a body, a resilient elastomer seat, a butterfly disk, a stem, packing, a notched positioning plate, and a handle. The resilient seat is under compression when it is mounted in the valve body, thus making a seal around the periphery of the disk and both upper and lower points where the stem passes through the seat. This resilient seat is held in place by mechanical means, and neither bonding nor cementing is necessary. Because the seat is replaceable, the valve seat does not require lapping, grinding, or machine work.

Butterfly valves are available in several body styles and seal types. The flange type or lug style can be held between flanges of any type. Wafer valves are installed between two flanges using bolts or nuts and studs, while lug style valves have metal inserts installed in the valve's bolt holes and the valve is installed between two flanges using a separate set of bolts for each flange. If the wafer style is used, avoid placing it between either slip-on or screwed flange types. Some wafer body styles will not form a proper seal. The wafer style is used more commonly and is cheaper than the lug style. The wafer type valve is designed for quick installation between flanges. No gaskets are required because of the molded resilient liner which is keyed into the recesses in both faces of the body ends. Packing is provided to form a positive seal around the stem for added protection in case the seal formed by the seat should become damaged.

Butterfly valves are relatively easy to maintain. They are lighter in weight than conventional valves. Butterfly valves are compact and space-saving and easily installed in new piping or as replacements in existing piping.

They are widely used in mechanical services as isolation valves on chilled and condenser water; the valves are designed so that lagging does not interfere with the valve operator.

Recommended Uses:
1. Fully open/closed or throttling services
2. Frequent operation
3. Minimal fluid trapping in line

Applications: Liquids, gases, slurries, liquids with suspended solids

Advantages:                        Disadvantages:
1. Low cost and maint.        1. High torque required for control
2. High capacity                   2.   Prone to cavitations at lower flows
3. Good flow control
4. Low pressure drop