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12 Types of Control: Valves Valves are used to control the flow in pipes and can be located anywhere along the pipe alignment. They are particularly applicable for pressurized conduits. There are many valve options available that can be used for flow regulation and the most commonly used are described below. Butterfly Valve: These valves were mainly used as on/off valves from their first use in the 1930s until the late 1970s, when design advancements made throttling more applicable (caution should still be used when butterfly valves are used as throttle valves). Since then, they have become the preferred system for most pipe applications because of their simplicity and reliability. Butterfly valves are used for a large range of conduit diameters and can be automatically or manually operated. They operate well for various pressure and flow conditions. When the valve is located near another component such as a pump, turbine, bifurcation or angle, a distance of six pipe diameters upstream and four pipe diameters downstream should be maintained between components to minimize turbulence effects on the operation of the valve. Butterfly valve shafts are typically oriented vertically with the actuator on top but the following applications require horizontally mounted shafts:  Water carrying heavy organic load or sedimentation (enhances flush effect)  When installed downstream of a centrifugal pump or any component inducing flow rotation around the vertical axis  When space limitations require the actuator be located on the side of the pipe Figure 2: Butterfly Valve, with chainwheel actuator for distant operation Figure 3: Typical relationship between percentage opening and disc position for a butterfly valve Figure 3 shows that disc position versus percent opening curve is not linear for butterfly valves. For example a valve disc open at 45 degrees and would result in a nearly 20% opening. Caution should be used when using them as throttling valves. Photo 5: Interior view of Butterfly Valve Ball Valve: When dealing with high pressure, ball valves are usually the best choice. Ball valves minimize vibration for highly pressurized conduits and provide relatively accurate flow control. They are often used as guard valves for downstream systems such as pressure reducing valves, turbines, or piping bifurcation. Ball valves have a low friction value when fully open and they can easily be found for diameters up to 48 inches.