A butterfly valve bolt chart is a reference table that maps valve size and flange standard to bolt count, diameter, length, and material grade.
Choosing the wrong bolt can shut down a project. Picking the wrong size can result in leaks, damaged flanges, and unplanned downtime. Consulting the butterfly valve bolt chart prevents those problems.
This article gives you the flange bolt size data you need for correct installation. It also covers flange standards, fastener material grades, and the most common mistakes teams make on-site.
What Is a Butterfly Valve Bolt Chart?
A butterfly valve bolt selection chart is a reference table for fastener selection. It maps valve size and flange standard to bolt count, bolt diameter, thread type, and minimum length.
The chart provides a specific guide to NPS or DN size and pressure class. Engineers use it to order the correct hardware before installation begins.
Installation teams also use the chart to confirm bolt size before torquing flanges. Procurement engineers use it to match fasteners to butterfly valve dimensions when ordering. Lastly, maintenance crews use it to verify replacement bolts meet the original specs.
Without the chart, this may affect the joint seal with either over-torqued undersized bolts or under-load larger bolts.
How Flange Standards Determine Bolt Selection
Flange standards dictate the bolt quantity, diameter, length, and material for each size and pressure class. ASME B16.5 and B16.47 standards provide the dimensions for bolt circles and hole spacing required for a proper, secure seal.
Always identify the flange standard first, as it dictates the required flange bolt size.
ASME Flanges
The ASME flange system follows ASME B16.5 for sizes up to NPS 24, and ASME B16.47 for larger diameters. Class 150 is the most common pressure rating for standard butterfly valve service.
Under ASME B16.5, bolt count and bolt circle diameter increase with pipe size.
For example, a 4-inch Class 150 flange uses eight 5/8-inch bolts. A 12-inch Class 150 flange uses twelve 7/8-inch bolts. These numbers are fixed by the standard, not by the valve manufacturer.
EN/DIN Flanges
European piping systems follow EN 1092-1 with pressure designations of PN6, PN10, and PN16. Metric bolt sizing applies throughout. An M16 stud at PN16 is not interchangeable with a 5/8-inch UNC bolt at ASME Class 150.
How to Use the ASME Class 150 Butterfly Valve Bolt Chart
To read the chart, look at the row which indicates the NPS/DN size. The columns tell you bolt count, diameter, thread series, minimum length, and material grade.
ASME Class 150 Bolt Chart (NPS 2 to NPS 24)
All dimensions reference ASME B16.5 Class 150. Stud lengths are minimum values for full thread engagement with standard gaskets.
| NPS (in) | DN (mm) | No. of Bolts | Bolt Dia. | Thread | Min. Length | Grade |
|---|---|---|---|---|---|---|
| 2″ | DN 50 | 4 | 5/8″ | UNC | 3.25″ | A193 B7 |
| 3″ | DN 80 | 4 | 5/8″ | UNC | 3.50″ | A193 B7 |
| 4″ | DN 100 | 8 | 5/8″ | UNC | 3.75″ | A193 B7 |
| 6″ | DN 150 | 8 | 3/4″ | UNC | 4.25″ | A193 B7 |
| 8″ | DN 200 | 8 | 3/4″ | UNC | 4.50″ | A193 B7 |
| 10″ | DN 250 | 12 | 7/8″ | UNC | 5.00″ | A193 B7 |
| 12″ | DN 300 | 12 | 7/8″ | UNC | 5.25″ | A193 B7 |
| 14″ | DN 350 | 12 | 1″ | UNC | 5.75″ | A193 B7 |
| 16″ | DN 400 | 16 | 1″ | UNC | 6.00″ | A193 B7 |
| 18″ | DN 450 | 16 | 1-1/8″ | UNC | 6.50″ | A193 B7 |
| 20″ | DN 500 | 20 | 1-1/8″ | UNC | 6.75″ | A193 B7 |
| 24″ | DN 600 | 20 | 1-1/4″ | UNC | 7.25″ | A193 B7 |
Butterfly Valve Cap Screw Chart Note
Wafer butterfly valves use through-bolts instead of stud bolts. The butterfly valve cap screw chart calculates total bolt length differently:
- Add the valve face-to-face dimension (per API 609 or ISO 5752).
- Add both flange thicknesses.
- Add nut height allowance for both ends.
How to Select Bolt Material Grades
Material grade affects both strength and corrosion performance. Hence, you should match the bolt grade to your operating medium and temperature, not just the flange bolt size.
- A193 B7 / A194 2H: Alloy steel studs and heavy hex nuts. Standard general-purpose service up to 450°C.
- A193 B8 / B8M: Stainless steel. Use in corrosive media, chemical service, or marine environments.
- A307 Grade B: Low-carbon steel bolts. Light-duty, low-pressure applications only.
Application Scenario: How to Read the Chart for a 6-Inch Water Treatment Application
A water treatment contractor needs to install an 8-inch butterfly valve on an ASME flange Class 150 line carrying treated water at ambient temperature. The contractor refers to the butterfly valve bolt selection chart and locates the NPS 8 row.
The chart shows the following:
- 8 bolts at 3/4-inch diameter
- UNC thread
- minimum 4.50-inch stud length
- A193 B7 grade with A194 2H nuts.
The medium is non-corrosive treated water, so A193 B7 is the correct material choice. There is no need to upgrade to stainless steel, which would also require recalculating torque values.
The contractor orders 8 sets of 3/4-inch x 4.50-inch B7 studs and 2H heavy hex nuts. They install the bolts using a cross-tightening pattern at the specified torque.
Common Installation Mistakes and How to Avoid Them
Most butterfly valve leaks are caused by three fastener errors. These mistakes can be prevented using the right dimensions and torque procedure.
Mistake 1: Wrong Cap Screw Length for Wafer Valves
Teams often pull bolt length from the NPS column alone and ignore flange thickness. A bolt that is too short does not engage full threads on both flanges. A bolt that is too long bottoms out before the flanges seat.
Calculate the cap screw length each time by using this formula:
Face-to-face + 2x flange thickness + 2x nut height.
The butterfly valve cap screw chart makes this calculation faster and avoids site substitutions.
Mistake 2: Sequential Tightening
Tightening bolts in clockwise order around the flange compresses the gasket unevenly. One side seats fully while the opposite side remains loose. The result is micro-gaps that leak under pressure cycling.
Always tighten in a cross or star pattern. Make at least two passes: a snug pass at 50% torque and a final pass at full specified torque.
Mistake 3: Mixing ASME and EN Flange Standards
An ASME flange at Class 150 and an EN 1092-1 flange at PN16 do not share the same bolt-hole pattern. Nominal pipe size matches, but the bolt circle diameter does not.
Mixing ASME flange hardware with EN-standard valve faces is a main cause of bolt-hole misalignment.
Conclusion
The first step to a leak-free installation is by consulting the butterfly valve dimensions chart. It is crucial to identify the ASME flange or EN standard and match it to the correct pressure class and nominal pipe size. Bolt counts and flange bolt sizes should also be pulled from the chart.
The wrong bolt length, mismatched flange standards, and sequential torquing all cause failures that shut down operations.
TG Valve manufactures butterfly valves ranging from 2 to 72 inches NPS, machined to precise ASME, EN, and API standards. Our bolt patterns align perfectly with standard flange bolt size requirements, ensuring easy, field-ready installation.
Backed by ISO 9001 certification, we supply global project sites with accurate butterfly valve dimensions and complete fastener compatibility data. Every valve ships with butterfly valve dimensions documentation and fastener compatibility data.
