Download Butterfly Valves - Torque, Head Loss, and Cavitation by American Water Works Association PDF

By American Water Works Association

During this ebook water operators obtain entire information regarding the flexible butterfly valve in consuming water carrier. Engineers and technicians will achieve a simple figuring out of calculations for working torque, head loss, and cavitation. assurance comprises valve layout, torque, head loss, cavitation, checking out, noise, and vibration.

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Additional resources for Butterfly Valves - Torque, Head Loss, and Cavitation Analysis - Manual of Water Supply Practices, M49

Example text

In. /ft) (m2/mm2) (continued) VALVE TORQUE 29 Units US Customary Variable Wdsls AP, Definition or Description Weight of the disc and shaft(s) assembly (banjo). For applications involving additional seismic loading, W,, may be multiplied by G or (Gil), where G is the additional gravitational acceleration multiplier. Pressure drop (or loss) while at disc angle 8 (SI-metric) lb (kg) psid (kPa) *Note: Equations 2-12,2-13,and 2-14 conservatively add the weight of the disc and shafts directly in the bearing friction calculation.

They are functions of disc geometry, valve travel, and pressure drop. Dynamic torque coefficients for an offset disc, also shown in Figure 2-15,depend on flow direction through the valve as well as disc geometry, valve travel, and pressure drop across the disc. The dynamic torque coefficient at the open position may be negative (giving the disc a tendency to open) when the valve is installed with the seat upstream. The offset disc torque coefficient can also change sign near the 85" position. If the valve is positioned at a n angle where torque direction is unstable (where C, crosses zero) for extended periods, damage caused by vibration may occur, and prolonged operation in this valve position should be avoided.

This value is usually a small component of total torque and is often ignored on larger valves. When the shaft seal is of the O-ring type or V-packing type, this component of torque is not significant and may be ignored. However, over-tightening of the shaft packing bolts or studs can cause a significant packing torque increase. Consult the valve manufacturer for packing adjustment instructions and recommendations. In some cases, this torque may be considered as a component of seating torque or of other frictional components of torque and may be assumed to be zero.

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