Most quotation problems on butterfly valves do not come from price or lead time. They come from an incomplete RFQ. A missing end connection or seat material means the offer is built on an assumption, and the assumption is discovered when the valves arrive at site. This article sets out the fields an enquiry needs and the attachments that let a supplier answer accurately first time.
The Core Fields, and Why Each One Matters
Nine pieces of information cover the great majority of butterfly valve enquiries:
- Size — DN or inch, for example DN200 or 8 inch.
- Pressure rating — PN10, PN16, Class 150 or Class 300.
- End connection — wafer, lug or double flanged.
- Body material — ductile iron, carbon steel or stainless steel.
- Disc material — which may differ from the body.
- Seat material — EPDM, NBR, PTFE or metal.
- Medium and temperature — water, oil, gas or steam, with normal and maximum temperatures.
- Actuation — manual, pneumatic or electric, and the fail position.
- Testing and documentation — pressure test standard, material certificates and inspection requirements.
Each of these changes the valve. Seat material decides the temperature limit and chemical suitability. End connection decides whether the valve can be used at a dead end and how it is bolted. Pressure rating decides wall thickness, flange drilling and often body material as well.
Size and Pressure Ratings
Write both size systems where you can. DN is a nominal metric size and inch is a nominal bore, so the two are labels for the same pipe size rather than exact dimensional conversions — DN100 corresponds to 4 inch nominal, and the actual bore depends on the pipe schedule. For pressure, PN and Class are different rating systems and must not be treated as interchangeable: they are broadly similar at ordinary temperatures but diverge as temperature rises, and they bolt to different flanges. Do not accept a Class 150 offer against a PN16 specification without confirming it, and specify the flange standard separately.
End Connection: Wafer, Lug or Flanged
The end connection is the field most often left out, and it carries real consequences:
- Wafer — the valve is clamped between two flanges by the line bolts. It is the most economical option and needs both flanges present to hold it. It cannot be used at a dead end.
- Lug — threaded or through-bolted lugs on the body allow the valve to be bolted to one flange, so the downstream pipe can be removed while the valve stays in place. Useful for pump isolation and for lines that are regularly opened.
- Double flanged — a flanged body bolted to both pipe flanges. It handles the highest loads and is common at larger sizes and higher classes.
If the line will be dismantled for maintenance, say so. If the valve sits at the end of a line in dead-end service, say so as well, because the permissible pressure may be lower than for a valve clamped between two flanges.
The Specification Fields Buyers Most Often Omit
Body, disc and seat materials
Body material is chosen for pressure, temperature and corrosion resistance, and the disc may match it or be upgraded. Seat material is where most of the temperature limit lives. EPDM is a good general choice for water and moderate steam service, while NBR is common for oil and gas but has a lower temperature ceiling. PTFE suits corrosive and higher-temperature duty, and metal seats are used where the temperature exceeds what any elastomer or polymer can survive. For chemical service, quote the actual concentration, because suitability depends on concentration and temperature together.
Fields that generate clarification emails
These are the items that most often prompt a question after the quotation has gone out:
| Field | What the buyer should state |
|---|---|
| Size | DN and inch, plus pipe schedule |
| Pressure and flange | PN or Class, plus flange standard and drilling |
| End connection | Wafer, lug or double flanged |
| Medium | Fluid name, concentration, and solids present |
| Temperature | Normal, maximum and minimum, including upsets |
| Duty | Isolation or throttling, and dead-end service |
| Actuation | Type, fail position, air or electrical supply |
| Documentation | Test standard, certificates, third-party inspection |
Testing and documentation
Shell and seat pressure testing for general industrial valves is commonly specified to API 598, so state the standard you want rather than leaving it open. Material certificates matter when the piping specification calls for traceability, and inspection requirements should be explicit: does the buyer want to witness the pressure test, review a mill certificate, or receive photographs before shipment? Where a project requires fire-safe qualification or a particular approval, name the standard in the RFQ. Reguvale holds ISO 9001 quality-system certification and SGS-CSTC factory audit reports; other standards are treated as project requirements and can be made available on request for qualified orders.
Common mistakes that delay a quotation
Three errors account for most of the back-and-forth. The first is leaving out the end connection, which changes both price and application limits. The second is mixing the PN and Class systems, for example asking for "PN16 Class 150" bolts, which does not describe a single flange. The third is giving the medium without the temperature, or the temperature without the concentration. Each omission forces the supplier either to guess or to ask, and both cost time. A short data sheet with the nine core fields removes almost all of it.
What to Attach, and How to Read the Reply
Attach the piping specification or line data sheet, the governing valve standard if the project names one (API 609, AWWA C504 or EN 593 for butterfly valves), and the quantity per size. Then check the reply against the same list. A usable quotation restates size, rating, end connection, body and seat materials, actuation, test standard and documentation, so any deviation is visible. If a quoted item does not match what you asked for, raise it before the order is placed.
Frequently Asked Questions
What is the single most important field on a butterfly valve RFQ?
The end connection, because it is the field most often omitted and it changes both the price and whether the valve can be used at a dead end. Size, pressure rating and seat material follow closely, since together they fix the temperature limit.
Can I write the size in DN only, or in inch only?
Either is acceptable if it is unambiguous, but stating both removes risk. DN is a nominal metric size and inch is a nominal bore, so they are labels rather than exact dimensional equivalents. Add the pipe schedule when the free bore matters for flow or pigging.
Is PN16 the same as Class 150?
No. They are different rating systems with different flange dimensions, and although PN16 and Class 150 are broadly similar at ordinary temperatures they diverge as temperature rises. Always pair the pressure rating with the flange standard so the drilling matches the pipe.
Which seat material should I specify for steam?
It depends on the temperature. EPDM is widely used in water and moderate steam duty, PTFE extends the range, and metal seats cover temperatures beyond elastomers. Give the normal and maximum temperatures and let the supplier confirm the seat against them.
What test standard should I ask for?
API 598 is the usual reference for shell and seat pressure testing of general industrial valves. The valve design standard is often named separately — API 609, EN 593 or AWWA C504 for butterfly valves. State both in the RFQ so the test certificate matches the specification.
A complete enquiry gets a faster, more accurate answer. Send the data sheet with the nine fields above, the flange standard and the quantity per size, and Reguvale will confirm each item rather than guess at it. Use request a quotation, or contact the sales team to send a piping specification directly. The butterfly valve range pages list the configurations available.