Bray 31U - Manual (Page 5)

Resilient Seated Butterfly Valves – Torques
All information herein is proprietary and confidential and may not be copied or reproduced without the expressed written consent of BRAY INTERNATIONAL, Inc.
The technical data herein is for general information only. Product suitability should be based solely upon customer’s detailed knowledge and experience with their application.
Introduction : 5
Angle of
Opening
0° 10° 20° 30° 40° 50° 60° 70° 75° 80° 90°
C
dt
0 0.0126 0.0140 0.0251 0.0505 0.0809 0.1394 0.2384 0.3419 0.401 0
Figure 2 - Angle of Opening
The C
dt
value for Bray symmetrical disc valves are approximately:
As shown in Figure 2, dynamic torque for Bray’s symmetrical disc
valves is at 0° angle of opening and increases until the angle of
opening reaches 75°-80°, where it then decreases to a zero value
at full open (90°) (no internal friction factors considered, just
dynamic torque only).
One final comment about dynamic torque is that one may minimize
the dynamic torque by the orientation of the valve (stem horizontal
or vertical) in the pipeline as well as by the location (distance) in
the pipeline from elbows, other valves, etc. (See Bray Resilient
Seated BFV Operations and Maintenance Manual).
D. Total Torque (T
T
)
The total torque required for operating a Bray symmetrical disc
butterfly valve at an angle opening between 0°and 90° is shown in
the Dynamic Torque section of this manual. Note that the dynamic
torque includes all internal friction torque values.
CONClUSION
In most applications for butterfly valves, especially 20˝ (508mm)
or smaller, the maximum torque required to operate the valve will
be seating/unseating torque. However, dynamic torque should be
considered particularly in:
• Control applications using larger valves (24˝ [610mm] and
above) where the disc is maintained in the open position
• Applications using larger valves (24˝ [610mm] and above)
where the velocity is high (16 ft./sec [5.3m/sec]).