5 only serving as a rough guide the valve losses in

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Unformatted text preview: y Guide 370 Chapter 6 Viscous Flow in Ducts 20.00 18.00 Gate 16.00 Disk Globe 14.00 12.00 K 10.00 8.00 6.00 4.00 2.00 0.00 0.25 Fig. 6.18b Average-loss coefficients for partially open valves (see sketches in Fig. 6.17). 0.30 0.40 0.50 0.60 0.70 0.75 0.80 0.90 1.00 Fractional opening h D 1000.00 100.00 K 10.00 80 1.00 20 30 40 0.10 50 60 70 90 Valve opening angle, degrees (b) The butterfly valve of Fig. 6.19a is a stem-mounted disk which, when closed, seats against an O-ring or compliant seal near the pipe surface. A single 90° turn opens the valve completely, hence the design is ideal for controllable quick-opening and quickclosing situations such as occur in fire protection and the electric power industry. However, considerable dynamic torque is needed to close these valves, and losses are high when the valves are nearly closed. Figure 6.19b shows butterfly-valve loss coefficients as a function of the opening angle for turbulent-flow conditions ( 0 is closed). The losses are huge when the opening is small, and K drops off nearly exponentially with the opening angle. Th...
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This note was uploaded on 10/27/2009 for the course MAE 101a taught by Professor Sakar during the Spring '08 term at UCSD.

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