Bray 31U - Manual (Page 20)

Resilient Seated Butterfly Valves – Flange Bolt Tensioning Data
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.
Mounting : 20
Flange Bolt Tensioning
Bray Butterfly Valves with Metal Mating Flanges
A question frequently asked at Bray is “What torque do
I apply to the flange bolts to insure the valve is properly
installed?”. Initially this seems to be a simple request
until all of the factors are analyzed. The installation of
a valve requires several components: the valve, mating
flanges, nuts, bolts and studs. Each is supplied by different
manufacturers and each has different characteristics. The
proper torque for one combination may be too much or
too little for a second combination. The following is a list
of information which needs to be known in order to start
calculating the torque requirements.
Valve
• Type
• Size
• Materials of construction (Body)
• Surface finishes / Surface conditions
Flange
• Type
• Size
• Finish / both sides
• Condition of flange / surface contamination
Bolt (or Stud)
• Type
• Materials of Construction
• Surface Conditions
Nut
• Type
• Materials of Construction
• Surface Conditions
Lubrication
• Type
• Coverage
General Factors
• Temperature and relative humidity at the time of
installation
• Speed at which bolts are turned
Note: The elastomer valve seat manufactured by Bray
also acts as the flange gasket. No additional gaskets are
required or recommended. Other valve styles which do
not have integral gaskets will need to have this component
supplied. The characteristics of this component will also
need to be considered.
Complete knowledge of all relevant conditions is almost
impossible to obtain. As a result, the computation of the
exact torque requirement is not practical. No reputable
manufacturer can provide accurate information when so
many outside factors are present.
The International Fasteners Institute covers some of the
details required to “compute” a torque value. Even with this
information the use of a torque wrench is only considered
to be 25% accurate. Based on the difficulty and inaccuracy
of using this method, Bray recommends the use of the
“Turn of the nut” method.
“Turn of the Nut” Tightening
(For ANSI Standard Iron and Steel Flanges)
**For Non-Metallic or non-standard flanges, follow the manufacturers installation
procedures.
1. The valve and flange faces must be aligned parallel to
each other.
Note: For rubber seated butterfly valves manufactured
by Bray, it is required that the valve be fully opened
prior to the tightening of the flange bolts.
2. After aligning the holes in a joint, sufficient bolts shall
be placed and brought to a ‘snug-tight’ condition to
ensure that the parts of the joint are
brought into full
contact with each other. ‘Snug-Tight’ is the tightness
attained by the full effort of a man using a spud wrench.
3. Following the initial snugging operation, bolts shall
be placed in any remaining holes and brought to snug-
tightness. Re-snugging may be necessary in large
joints.
4. Tighten opposite bolts in sequence to insure even
pressure around the entire flange.