Butterfly Valves

View A Video on Butterfly Valves- A Quick Introduction

Though butterfly valves are fairly simple, butterfly valve manufacturers have made varying kinds available. High performance butterfly valves are used in systems with very high pressures; pneumatic butterfly valves are typically used with pressurized air at much lower pressures. The unique butterfly valve design of triple offset butterfly valves provides the tightest seal by being mounted in three positions. Other variations come from the way the valve is connected with the piping. Flanged butterfly valves have raised outside edges that are part of the enclosure itself. These built-in flanges allow the valve to be bolted in between pipes. Alternately, wafer butterfly valves are typically sandwiched between two flanges using bolts and nuts. Lug butterfly valves are a third option. Another difference is whether the control lever is manually operated or automatic. Electric butterfly valves use a direct mount electric actuator to do the work of moving the shaft, eliminating the need for an operator to physically crank the wheel. Common materials used are plastic butterfly valves, stainless steel butterfly valves and cast iron butterfly valves. Finally, butterfly valves are made to different standards for safety and efficiency reasons. AWWA butterfly valves are certified to meet the American Water Works Association's regulations.

Butterfly valve manufacturers use three main materials when constructing these mechanisms. Because these valves come into contact with potable water, they must be as sanitary and safe as possible, including carefully chosen and appropriate materials. Plastic butterfly valves are the least common. The body and disc are made of thermoplastic materials that are molded into a strong, one-piece design. Plastic butterfly valves are a very cost effective option. However, they should not be used with harsh chemicals that could wear away at the disc, causing an imperfect seal. Stainless steel butterfly valves are made of stainless steel materials. Stainless steel is a metal that is resistant to corrosion and oxidation. It is chosen over other metals and traditional steel because it has a longer life and requires less maintenance. Stainless steel is also highly sanitary and easy to clean therefore making it the best option for applications involving food products and drinkable liquids. Cast iron butterfly valves are used in heavy duty scenarios because the casting process toughens and hardens the iron into a very durable material.

The most important aspect of all the varying kinds of valves is the butterfly valve design. For example, manufacturers must take into account the properties of the material and how they fabricate the pieces of the valve. Sometimes the shaft is one solid rod while other designs use two pins instead. The general design of butterfly valves has not changed much since they were first developed. The concept behind them is simple; a disc rotates to plug the width of the pipe. However, there have been advancements in materials, machining processes and fabrication techniques. The characteristics of steel and iron alloys when they come into contact with certain pressures, temperatures and substances have been widely researched so that there are no surprises when the actual valve is installed in the pipe line. Better machining such as CNC (computer numeric controlled) processes allow the discs and enclosures to be cut to very precise measurements for the tightest fit with minimal clearance. A large range of sizes is now available that can be used in standard and custom sizes, which allows more industries to benefit from using butterfly valves.

Butterfly valves are used in a range of environments, partly because they can act as throttles to control the flow of a fluid without completely closing the pipe. With recent innovations in fabrication techniques, these valves are made with very few flaws. The metal is even and smooth with a minimum of internal stresses. Bolt holes and flanges are carefully crafted to meet the standards of the valve and to ensure that they are not weak points for the mechanism and the assembly of the seal, disc and shaft is tested before being installed in the enclosure. Also, their ability to work with a variety of substances means they can be purchased by more companies and industries. Butterfly valves can block and control the flow of gases, such as air, liquids, such as water or petroleum, and mixtures of solids such as slurries. Specific applications include chemical transport, underground piping systems, high pressure water lines and carburetors. Industries that utilize butterfly valves include pipe fabricators, automotive, waterworks companies, irrigation industries, food processing and industrial manufacturers.

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Butterfly Valve Types

• Aluminum butterfly valves use various grades of aluminum for their makeup. Aluminum is commendable for its ultra lightweight and above average strength, but unlike stainless steel, aluminum is prone to corrosion over time.
• AWWA butterfly valves meet standards put in place by the American Water Works Association because they are used to transport potable water.
• Butterfly valve design is the most important consideration for choosing a valve; the three main styles are lug, wafer and flanged butterfly valves.
• Butterfly valve manufacturers are industrial companies that make butterfly valves.
• Cast iron butterfly valves are frequently used in heavy duty environments with harsh conditions because of the metal's strength.
• Electric butterfly valves use an electric actuator to open and close the valve instead of a hand operated lever or crank wheel.
• Flanged butterfly valves have raised outer rims that allow them to be installed in between two pipes so one side may be disconnected without having to disrupt the entire piping system.
• High performance butterfly valves are typically double offset valves that can withstand both high temperatures and pressure.
• Lug butterfly valves are valves that have threaded metal inserts in the bolt holes that allow a system to use two sets of bolts without nuts. Lug valves are installed between two flanges and are used to disconnect one side of the piping system without distributing the other.
  
• Plastic butterfly valves are cheap and offer higher flexibility than their metal counterparts. With these benefits, a lower maximum pressure and temperature stability are to be expected.
• Pneumatic butterfly valves are used to shutoff pipes that transport compressed or pressurized air
• Stainless steel butterfly valves are the most common type of butterfly valves. Stainless steel is used for its strength and anti-corrosive properties.
• Triple offset butterfly valves are mounted eccentrically in three places to help create a tighter and stronger seal.
• Wafer butterfly valves are installed between two flanges and are secured using bolts or nuts and studs.

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Butterfly Valves Terms Actuator - The part of a valve that converts electrical, fluid or thermal energy into mechanical energy in order to open/close the valve. Aeration - The process of mixing air with a high content of oxygen into a liquid. Carburetor butterfly valves go through aeration when mixing oxygen with fuel. Backpressure - Force on the upstream part of a butterfly valve or valve seat. Bearing - A support typically used in conjunction with butterfly valves to hold the revolving shaft in its appropriate position. Blind Flange - A solid plate-like fitting used to seal a flanged end pipe's end. Bonnet - The part of a valve that connects the body to the valve actuator. The bonnet sometimes includes the stem packing. Breakaway (Unseating) Torque - The turning force required to rotate the closure element of a butterfly or rotary valve. Flange - The rim at the end of a fitting, pipe or valve that allows for bolting onto an additional pipe element. Flow Meter - A device used to read and signify the flow rate of a material. Flow Rate - The weight, mass or volume of a gas, liquid or solid through a medium per unit of time. Gate Valve - A valve similar to a butterfly valve. Gate valves are not used in throttling applications because they are either entirely open or entirely closed. Inlet - Area of a valve through which fluid enters. Leakage - The amount of fluid that passes through a valve while it is in the off position. The most common unit for measuring leakage is in volume/time. Outlet - The opening in a valve through which fluid exits. Pounds per Square Inch (PSI) - A unit of measurement that signifies the level of pressure of a liquid, solid or gas in a valve system. Recovery - The amount of pressure in a flow stream that is reduced as a direct result of the design of the control valve. Recovery is also described as the ratio of maximum downstream pressure to upstream pressure. Seating Torque - The value of the turning force that is needed to close a valve. Slip on Flange - A flange that slides over the end of piping and is then welded in place. Throttling - Regulation of flow or current through a valve. Trim - The inner parts of a valve that are in contact with the flow stream. Valve Body - The main part of a valve that contains passages for the flowing material. Variable Speed - Term for when an actuator is able to provide a slower operating time over the entire range of operation. Vena Contracta - The area of a valve at which the flow stream is the slowest, usually downstream of the physical constriction.

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