Bray 31U User Manual
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A Division of BRAY INTERNATIONAL, Inc.
Resilient Seated Butterfly Valves
Technical Manual
TM1050 - 10/30/2012
Resilient Seated
Butterfly Valves
Technical Manual - Table of Contents
Topic Page(s)
Introduction to Torques ........................................3
Reduced Disc Diameter Bray Valves 30/31/3A ..6
Seating & Unseating Torques .............................. 7
20/21, 30/31 Imperial (Lb-Ins) ...............................8
20/21, 30/31 Metric (N-m) ....................................9
32/33, 35/36 .........................................................10
Imperial (Lb-Ins) & Metric (N-m)
22/23 Imperial (Lb-Ins) & Metric (N-m) ................11
Dynamic Torque Factors
Imperial (Lb-In/psi) ................................................12
Metric (N-m/bar) ................................................... 13
Valve Sizing Coefficients .................................. 14
Imperial (Cv) ......................................................... 15
Metric (Kv) ............................................................ 17
Flange to Valve Bolting Guide ............................. 19
Flange Bolt Tensioning Data ................................ 20
Standard Metal Specifications
20/21 & 22/23 .......................................................23
30/31, 31H, 3A/3AH, 31U ......................................24
32/33, 35/36, 35F, 36H .......................................... 25
All statements, technical information, and recommendations in this bulletin are for
general use only. Consult Bray representatives or factory for the specic requirements
and material selection for your intended application. The right to change or modify
product design or product without prior notice is reserved.
Resilient Seated Butterfly Valves – Torques
Torques
INTRODUCTION
There are a number of torques which buttery valves may
experience such as:
Tsu - Seating and Unseating Torque
Td - Dynamic Torque Resulting from uid ow
T
– Bearing Friction Torque
bf
Tss – Stem Seal Friction Torque
Te – Eccentricity Torque resulting from
disc offset from centerline of stem (either single,
double or triple offset)
Th – Hydrostatic Torque
Factors which inuence the buttery valve torque values
shown above are:
Type of Seat and Seat Material
Interference of Seat I.D. and Disc O.D.
Shaft Diameter
Valve Diameter
Bearing Coefcient of Friction
Angle of Opening
Shut-off Pressure
Fluid Velocity
Disc Shape and Conguration
Piping System and Location/Orientation of Valve in Pipe Line
System Head Characteristics
Physical Size of Disc/Shaft Obstructing Flow
Disc Edge Finish
With respect to Buttery Valves, the two major conditions for
determining total valve operating torque (TT) exists as follows:
CASE I (Angle = 0° , Disc in Closed Position)
TT = Th + Tbf + Tss+ T
Analyzed
Total Torque for Case I using a symmetrical disc buttery valve is
the sum of hydrostatic torque, bearing friction torque, stem seal,
friction torque, and seating/unseating torque.
A. Hydrostatic Torque (Th)
We will ignore discussion of the hydrostatic torque values as they
are generally insignicant compared to the seating/unseating,
bearing friction and stem seal torque values (the safety factor
applied to seating/unseating, stem seal friction and bearing
friction torque values more than compensates for the hydrostatic
torque which is usually less than 2% of these total torques).
B. Bearing Friction Torque (Tbf)
Bearing friction torque occurs because pressure forces against
the disc are transmitted to the stem. As the stem is forced against
the bearing supports, bearing friction torque is created between
the stem material and the support material as the stem is turned.
Bearing friction torques are normally included in the seating/
unseating torque values.
Bearing friction torques can be determined by using
the following equation:
Tbf = .785 Cf D
Where:
Tbf = Bearing Friction Torque
Cf = Coefcient of Friction (approximately .25 for non-
corroded stem to cast iron body) (dimensionless).
Dv = Valve Diameter (Inches)
d = Diameter of Shaft (Inches)
∆P = Pressure Differential (psi)
su
2
(d/2) ∆P
v
Introduction : 3
C. Stem Seal Friction Torque (Tss)
For all practical purposes stem seal friction torque values are
insignicant when compared to seating/unseating and bearing
friction torques. Stem seal friction torques are normally included
in the seating/unseating torque values.
All information herein is proprietary and condential 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.
Resilient Seated Butterfly Valves – Torques
D. Seating/Unseating Torques (Tsu)
The seating/unseating torque value (Tsu) is a function of the
pressure differential, the seat material’s coefcient of friction,
the nished surface of the disc edge, the amount of interference
between the seat I.D. and disc O.D. when anged in piping, the
seat thickness, and the type of service (media) for which the valve
is being used. In determining the Tsu values for Bray resilient
seated buttery valves, Bray has developed Seating/Unseating
Torque Charts incorporating all bearing friction and stem seal
friction torques for three classes of services for both the valves
with standard discs (rated to full pressure) and for valves with
reduced diameter discs (rated for 50 psi [3.5 bar]). The three
service classes are:
Class I – Non-Corrosive, Lubricating Service
Class II – General Service
Class III – Severe Service
Please review the guidelines for each class in the technical
manual when determining which Seating/Unseating Torque Class
should be used. Most buttery valves are used in Class II, General
Service applications.
E. Total Torque (TT)
The total torque values for Bray symmetrical disc valves for Case
I applications are shown in the Seating/Unseating Torque Charts
within this manual.
CASE II
(Disc in Partial To Full Opening Position)
TT = Tbf + Tss+ T
d
The total Torque for Case II using a symmetrical disc buttery valve
is the summation of bearing friction torque, stem seal friction torque
and dynamic torque.
A. Bearing Friction Torque (T
)
bf
See Case I discussion. This torque value is normally included in
the Dynamic Torque Value.
B. Stem Seal Friction Torque (Tss)
See Case I discussion. This torque value is normally included in
the Dynamic torque value.
C. Dynamic Torque (Td)
In a symmetrical disc design, dynamic torque occurs between the
closed position, 0° and the full open position, 90°. With the disc in
the partially open position, velocity of the uid passing the leading
disc edge is less than the velocity passing the trailing edge. This
variance in velocity past the leading disc edge and trailing disc
edge results in an unbalanced distribution of pressure forces on
the upstream side of the face of the disc. The total pressure forces
acting perpendicular to the disc face on the leading edge half of
the disc are greater than the total pressure acting perpendicular on
the trailing half of the disc. This uneven distribution of pressure on
the disc face (exists on both sides of the disc) results in a torsional
force which tries to turn the disc to the closed position (Figure 1).
This torsional closing force can become greater than the seating/
unseating torque value depending on the valve angle of opening
and differential pressure.
To determine dynamic torque, the following equation is applied:
T
= C
d
3
d
∆P
dt
Where:
Td = Dynamic Torque (lbs- in).
Cdt = Coefcient of Dynamic Torque (based on disc shape
and angle of opening) (dimensionless)
d = Diameter of Disc (Inches)
∆P = Pressure Differential Across Valve (psi)
Introduction : 4
Figure 1 - Pressure Distribution
C
l
o
Pressure Forces
FLOW
All information herein is proprietary and condential 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.
s
i
n
g
T
o
r
q
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e
MORE
TURBULENCE
HERE
Resilient Seated Butterfly Valves – Torques
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 nal 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
buttery 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.
Figure 2 - Angle of Opening
The Cdt value for Bray symmetrical disc valves are approximately:
CONCLUSION
In most applications for buttery 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]).
Angle of
Opening
C
dt
0° 10° 20° 30° 40° 50° 60° 70° 75° 80° 90°
0 0.0126 0.0140 0.0251 0.0505 0.0809 0.1394 0.2384 0.3419 0.401 0
Introduction : 5
All information herein is proprietary and condential 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.
Resilient Seated Butterfly Valves – Torques
Reduced Disc Diameter
Bray Series 30/31/3A Valves
Bray offers a reduced disc diameter for 4”-20” for Series 30, 31
and 3A valves. The purpose of reducing the disc diameter is to
decrease the seating/unseating torques and extend the seat life on
low pressure applications.
By reducing the disc diameter, the interference between the disc
O.D. and seat I.D. is decreased and the valve pressure rating,
which is a function of this interference, is reduced to 50 PSI. Less
interference between the disc and seat results in reduced seating/
unseating torques. Lower seating/unseating torque may allow for
the use of a smaller actuator on the valve. In other applications
where abrasive dry bulk materials such as cement, sugar, plastic,
pellets, our, etc., are generally pneumatically conveyed at 50
PSI or less, the reduced disc diameter not only reduces the seat-
ing/unseating torque but, very importantly, usually signicantly
increases the service life of the seat.
Bray does the following to differentiate reduced diameter discs
from full diameter discs:
Metal Discs: An “ R ” is stamped above the part number
Nylon 11 Coated Discs: Discs are differentiated by the color of
the Nylon 11:
Grey – Full Disc Diameter
White – Reduced Disc Diameter
Introduction : 6
All information herein is proprietary and condential 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.
Resilient Seated Butterfly Valves – Seating & Unseating Torques
Seating & Unseating Torques
Bray has developed Seating/Unseating Torque Charts for three
Classes of Service for its valves with standard discs (rated for
full pressure) and for valves with reduced diameter discs (rated
for 50 PSI / 3.5 bar.).
Characteristics of
Application
Media Type
Corrosion
by Media
Chemical
Reactions of Media
with Seat
Media
Temperature
Non-Corrosive, Lubricating Service
Class A
Lubricating hydrocarbons;
Aqueous processes and Water
(See Note 1)
Insignificant if any
Insignificant if any
45º to 160ºF
(7º to 71ºC)
The guidelines for selecting a Class to be used for determining
a valve’s seating/unseating torque are given below. Each valve
application should comply with all ve Class characteristics in
order to be qualied for that Class.
Class B
General Service
Water; aqueous processes; all
other aqueous liquids including
salt water; Lubricating gases
No major corrosion or deposits
from media
Only minor or insignificant in
nature
Within seat temperature limits,
not near limits
Dry, non-lubricating such as air,
Reactions causing swelling and
Class C
Severe Service
dry gas, cement, pneumatic
conveying mediums
Can incur significant
corrosion such as Ductile Iron
disc in water
hardness occur
Near or at seat temperature
limits
Frequency of
Valve Cycling
Once weekly or more frequently
NOTE:
1. For aqueous processes and water, Class A torques may be
used only if a Nylon 11 coated disc is selected and all other
Class A characteristics apply. Otherwise, Class B torques
should be used.
2. All the material trims may be classied into Class A, B, or
C except Series 20/21 valves with a PTFE Lined Elastomer
seat, PTFE molded disc/stem, or rubber molded disc/stem.
These trims must always use Class C Seating/Unseating
Torque Values unless they are used only in a throttling
application. Valves with bonded seats must always be
classied as Class C.
3. If a valve is used strictly in a throttling application, that is,
it is never put in the closed position but throttled between
20° and 80°, then Class A torques may be used provided
you have checked to see that dynamic torques do not
exceed the Class A torque values.
Minimum once every 3-6 weeks,
or more frequently
Infrequently, sometimes not
cycled for long periods
4. With the exception of dry, non-lubricating medias, one
is usually safe electing to use Class B torques for sizing
actuators for all other valve service applications. Seating/
Unseating Torque values shown include friction bearing
torques for stated differential pressure.
5. Dynamic Torque values are not considered.
See the Dynamic Torque chart in this manual for
determination of Dynamic Torque.
6. Do not apply a safety factor to torque values when
determining actuator output torque requirement.
7. For 3-way assemblies where one valve is opening and
another is closing, multiply torque by a 1.5 factor.
Torque : 7
All information herein is proprietary and condential 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.
Class A
Non-Corrosive,
Lubricating
Service
Valve
Size
Inches
1
1.5
2
2.5
3
4
5
6
8
10
12
14
16
18
20
Resilient Seated Butterfly Valves – Seating & Unseating Torques
Series 20/21 and 30/31/3A Torques (Lb-Ins)
Valve Differential Pressure (PSIG)
Full Disc Reduced Disc
0 psi 50 psi 100 psi 150 psi 175 psi 0 psi 50 psi
54 59 65 70 73 54 59
81 86 91 97 100 81 86
109 114 119 123 128 109 114
169 178 187 196 200 169 178
220 236 250 264 273 220 236
341 364 387 410 423 225 248
510 560 610 660 687 324 374
632 712 792 872 912 344 488
1,182 1,341 1,500 1,660 1,741 735 894
1,764 2,018 2,272 2,526 2,653 1,204 1,358
2,701 3,110 3,519 3,928 4,132 1,665 2,074
3,818 4,500 5,182 5,864 –– 2,318 3,000
4,638 5,819 7,000 8,182 –– 2,699 3,880
5,265 7,065 8,865 10,665 –– 2,970 4,788
7,000 9,364 11,728 14,091 –– 3,356 6,243
Class B
General Service
Class C
Severe Service
1.5
2.5
10
12
14
16
18
20
1.5
2.5
10
12
14
16
18
20
1
2
3
4
5
6
8
1
2
3
4
5
6
8
59 65 71 77 80 59 65
89 95 100 106 110 89 95
120 125 130 135 140 120 125
185 195 205 215 220 185 195
245 260 275 290 297 245 260
375 400 425 450 462 252 267
560 615 670 725 755 355 410
695 783 871 953 1,003 427 537
1,300 1,475 1,650 1,825 1,915 808 983
1,960 2,240 2,520 2,800 2,940 1,213 1,493
2,970 3,420 3,870 4,320 4,545 1,830 2,280
4,200 4,950 5,700 6,450 –– 2,550 3,300
5,100 6,400 7,700 9,000 –– 2,967 4,267
5,850 7,850 9,850 11,850 –– 3,267 5,267
7,700 10,300 12,900 15,500 –– 4,267 6,867
74 82 89 97 100 74 82
111 119 125 133 137 111 119
151 157 163 169 175 151 157
231 244 257 269 275 231 244
306 325 344 363 375 306 325
468 500 532 563 582 316 348
700 769 838 907 944 444 513
870 980 1,090 1,200 1,255 525 672
1,625 1,844 2,063 2,282 2,394 1,011 1,230
2,450 2,800 3,150 3,500 3,675 1,517 1,867
3,712 4,275 4,838 5,400 5,682 2,287 2,850
5,251 6,188 7,125 8,063 –– 3,189 4,126
6,375 8,000 9,625 11,250 –– 3,709 5,334
7,315 9,815 12,315 14,815 –– 4,084 6,584
9,625 12,875 16,125 19,375 –– 5,334 8,584
Torque : 8
All information herein is proprietary and condential 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.
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