Bray 31U - Manual (Page 7)

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.
Resilient Seated Butterfly Valves – Seating & Unseating Torques
Torque : 7
Seating & Unseating Torques
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 classified 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
classified 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.
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.
Characteristics of
Application
Class A
Non-Corrosive, Lubricating Service
Class B
General Service
Class C
Severe Service
Media Type
Lubricating hydrocarbons;
Aqueous processes and Water
(See Note 1)
Water; aqueous processes; all
other aqueous liquids including
salt water; Lubricating gases
Dry, non-lubricating such as air,
dry gas, cement, pneumatic
conveying mediums
Corrosion
by Media
Insignificant if any
No major corrosion or deposits
from media
Can incur significant
corrosion such as Ductile Iron
disc in water
Chemical
Reactions of Media
with Seat
Insignificant if any
Only minor or insignificant in
nature
Reactions causing swelling and
hardness occur
Media
Temperature
45º to 160ºF
(7º to 71ºC)
Within seat temperature limits,
not near limits
Near or at seat temperature
limits
Frequency of
Valve Cycling
Once weekly or more frequently
Minimum once every 3-6 weeks,
or more frequently
Infrequently, sometimes not
cycled for long periods
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.).
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 five Class characteristics in
order to be qualified for that Class.
NOTE: