Valve markings explained simply: the letters, numbers, arrows, and cast codes on a valve are the first checks before installation, replacement, or purchase. A mark such as DN80, PN16, Class 300, WCB, CF8M, or a flow arrow can affect whether the valve matches the pipe, pressure rating, material requirement, and flow direction.
These markings are useful, but they are not the full specification. A body mark may show the size and material, while a nameplate or tag may carry the pressure class, standard, serial number, actuator data, or service limit. For a buyer or maintenance team, the risk is reading one mark correctly but missing the condition behind it, such as temperature, media, end connection, or the standard used for the rating.
This guide shows how to read common valve body markings, nameplate data, pressure rating codes, material codes, and standard references in a practical order. It also explains when to compare the markings with datasheets, test records, and valve standards and documents before approving a valve for service.
What Valve Markings Tell You Before Installation or Replacement
A valve marking is a quick identification check, not a full design approval. It can tell you whether the valve looks close to the required size, pressure rating, material, flow direction, and standard, but it still needs to be checked against the datasheet, line list, purchase order, or inspection document.
When a maintenance team sends a valve photo for replacement, the useful marks are usually the ones that answer these first questions:
- Who made the valve, or which brand or foundry mark is shown?
- What is the nominal size, such as DN80, NPS 3, or 3 inch?
- What pressure rating is shown, such as PN16, Class 150, Class 300, CWP, WOG, or SWP?
- What body material or casting code appears, such as WCB, CF8, CF8M, WC6, or WC9?
- Is there a flow arrow, especially on check valves, globe valves, control valves, or pressure-reducing valves?
- Does the valve show a design or marking standard, such as ASME, API, MSS, ISO, GB, EN, DIN, or JIS?
- Is there a serial number, heat number, tag number, or other traceability code?
These marks help narrow the valve identity, but they do not always show the seat material, trim material, gasket material, actual temperature limit, leakage class, test pressure, or special service requirement. For steam, corrosive media, high temperature, oxygen service, or frequent cycling, the marking should be treated as the starting point for verification, not the final answer.
Valve Body Markings vs Nameplate Tags
The first check is where the information is marked. Valve body markings are usually cast, forged, stamped, or engraved on pressure-retaining parts such as the body, bonnet, flange, or end connection. These marks are hard to remove, so they are useful when a valve has been in service for years and the original paperwork is missing.
Nameplates and tags carry information that may be too detailed for the casting, such as model number, serial number, tag number, actuator data, test reference, or special service limits. According to ISO 5209, markings for general purpose industrial valves may appear on the body, flange, identification plate, or another suitable location, so the reader should check more than one surface before deciding what the valve is.
A body mark should not be confused with a plant tag. A plant tag such as CV-204, XV-102, or P-15 may identify the valve position in the piping system, but it does not prove the valve material, pressure class, or manufacturing standard. For replacement work, use the plant tag to find the line record, then compare the physical valve markings with the datasheet, inspection document, and purchase specification.
This distinction matters when the valve has several data points in different places. The body may show WCB or CF8M, the flange may show Class 150 or PN16, the plate may show a serial number, and the actuator may have its own air supply or voltage data. Reading only one location can lead to a close-looking replacement that fails the real service requirement.
How to Read Common Valve Marking Items
Read valve markings in a fixed order. Start with the marks that identify the valve, then move to the marks that affect whether it can work in the line. This avoids a common mistake: seeing the right size first, then missing the pressure class, material, or flow direction.
If you are checking a replacement valve from a photo, ask for a clear view of the body, both flanges or ends, the nameplate, and any tag fixed to the actuator or handwheel. One photo rarely shows all the useful information.
| Marking item | What it usually tells you | What to verify next |
|---|---|---|
| Manufacturer name or logo | Who made or supplied the valve | Match it with the datasheet or purchase record |
| DN, NPS, or inch size | Nominal valve size, not always exact bore size | Check pipe size, end connection, and DN and PN meaning in valves |
| PN, Class, CWP, WOG, or SWP | Pressure rating system or service pressure clue | Confirm material, temperature, medium, and standard |
| WCB, CF8, CF8M, WC6, WC9 | Body or casting material family | Check the material certificate and corrosion requirement |
| Flow arrow | Required flow direction | Check before installing check, globe, control, or reducing valves |
| API, ASME, MSS, ISO, GB, EN, DIN, JIS | Design, marking, test, or dimensional standard family | Confirm the exact standard and edition in the documents |
| Serial, heat, or tag number | Traceability or plant location reference | Match it with MTC, inspection report, or line list |
Use the table as a reading sequence. If the size and pressure rating look right but the material code, flow arrow, or standard does not match the line record, stop and verify before ordering or installing the valve.
Pressure Rating Markings: PN, Class, CWP, WOG, and SWP
The pressure mark is one of the easiest valve markings to misread. PN16 does not mean every valve with that mark is safe for all 16 bar services, and Class 150 does not mean a simple 150 psi limit. These marks point to a rating system, then the actual allowable pressure depends on the valve material, temperature, medium, and standard.
For ASME valves, ASME B16.34 covers pressure-temperature ratings, materials, dimensions, testing, and marking. That is why a Class 300 WCB valve and a Class 300 stainless steel valve should still be checked against the correct pressure-temperature table before use.
| Marking | Common meaning | Main caution |
|---|---|---|
| PN16, PN25, PN40 | Nominal pressure rating used in metric/EN/GB-style systems | Check temperature, material, and flange standard before treating PN as usable pressure |
| Class 150, 300, 600 | ASME/ANSI pressure class designation | It is not a direct psi value; use the pressure-temperature rating table |
| CWP | Cold working pressure | Usually for non-shock cold service; not enough for hot oil, steam, or high-temperature lines |
| WOG | Water, oil, gas rating under stated conditions | Do not use it as a steam or corrosive-media rating without manufacturer data |
| SWP or WSP | Steam working pressure | Check steam temperature, seat material, packing, and test record |
When a valve marking shows both PN and Class, do not convert them by memory. Compare the full standard, flange drilling, body material, and temperature range. For a deeper comparison, use the MacoTango guide to ANSI Class vs PN before choosing a replacement valve.
Material and Casting Codes on Valve Bodies
Material codes on a valve body are usually casting or forging material clues. They help the buyer check whether the body material matches the medium, temperature, corrosion risk, and purchase specification. They should not be treated as a complete material certificate.
For example, WCB is commonly seen on cast carbon steel valve bodies. It may suit many water, oil, gas, and general process lines, but it is not stainless steel and it should not be accepted for corrosive service without checking the medium and material requirement. CF8 and CF8M point to stainless steel casting families, often used where corrosion resistance matters more than plain carbon steel.
WC6 and WC9 need extra care because they are alloy steel casting codes, often connected with higher-temperature service. WC9 should not be described as cast carbon steel. If a replacement valve photo shows WC9, the buyer should check the line temperature, pressure-temperature rating table, material certificate, and original valve specification before choosing an alternative.
The body code also does not confirm the trim, seat, gasket, packing, or bolting material. A valve body may be WCB while the seat is PTFE, metal seated, Cr13, STL, or another trim arrangement. For real approval, compare the body marking with the datasheet, MTC, pressure test report, and product specification, such as the way MacoTango lists size, pressure, material, and standards on its worm gear ball valve specifications.
Standards Behind Valve Markings
A valve marking only makes sense when you know which standard system it belongs to. The same letters or numbers can be misunderstood if the buyer reads them outside the correct design, pressure, material, or marking standard.
For industrial valves, the most useful standards are not all doing the same job. Some explain where markings may appear, some define what must be marked, and others control the pressure-temperature rating behind the mark.
- ISO 5209 gives marking guidance for general purpose industrial valves, including marking locations such as the body, flange, identification plate, or another suitable place.
- ANSI/MSS SP-25 is a common reference for marking systems on valves, fittings, flanges, and unions used in piping connections.
- ASME B16.34 is not only a marking reference. It also covers pressure-temperature ratings, materials, dimensions, testing, and other valve requirements. MacoTango has a separate guide to the ASME B16.34 standard for buyers who need deeper context.
- API 6D is mainly relevant to pipeline valves. If API 6D appears in a specification, check the order document, test record, and product scope instead of assuming it from a body mark alone.
The safe reading method is simple: use the marking to identify the likely standard family, then confirm the exact standard, edition, valve type, material, pressure class, and test document. A cast mark is useful evidence, but it is not a substitute for the approved datasheet or inspection record.
Markings by Valve Type: Ball, Gate, Globe, Butterfly, and Check Valves
The same marking item can carry different weight on different valve types. Size, pressure class, and material are always useful, but flow direction, trim, end connection, or seat type may become the deciding point for some valves.
When comparing a replacement valve, read the marks against the valve function first. A shut-off ball valve, a throttling globe valve, and a check valve do not fail in the same way when the wrong detail is missed.
Ball Valves
For ball valves, the key markings are usually size, pressure rating, body material, bore type, and end connection. A mark may show DN, NPS, PN, Class, WCB, CF8M, or a standard reference, but it may not tell you whether the valve is full bore, reduced bore, floating ball, trunnion mounted, soft seated, or metal seated.
If the valve is for isolation in oil, gas, water, steam, or chemical service, compare the body mark with the datasheet and seat material before ordering. For product family context, MacoTango lists related options in its ball valve series.
Gate and Globe Valves
Gate valves are often checked for size, pressure class, body material, wedge or seat arrangement, and end connection. The body mark may confirm the pressure shell, but the buyer still needs the trim and seat details if the valve is used in steam, high-temperature oil, or abrasive service.
Globe valves need extra attention to flow direction and trim. A globe valve can create higher pressure drop than a gate valve, and some designs have a preferred flow direction. If the body shows an arrow, do not treat it as decoration.
Butterfly Valves
For butterfly valves, the useful markings often include DN, PN or Class, body material, disc material, liner or seat material, and connection style. Wafer, lug, and flanged butterfly valves can look similar in photos, so the end connection should be checked against the pipe flange standard before replacement.
Seat material matters here. EPDM, NBR, PTFE, metal seat, and other seat options can change the suitable medium and temperature range even when the body pressure mark looks correct.
Check Valves
For check valves, the flow arrow is one of the most important marks. A swing check, lift check, dual plate check, or silent check valve must face the correct flow direction, or it may not stop reverse flow as intended.
Size, pressure class, and material still matter, but orientation and installation position can be just as critical. When replacing a check valve, compare the arrow, valve type, face-to-face length, flange standard, and spring or disc design. MacoTango groups related products under its check valve series.
Common Reading Mistakes and Inspection Checks
Most valve marking mistakes happen because one visible mark looks convincing. A clear DN, PN, Class, or material code can make the valve look correct, even when another mark or document points to a mismatch.
Use the checks below before approving a replacement valve, accepting a shipment, or installing a valve from stock.
| What you see | Common mistake | Inspection check |
|---|---|---|
| Class 150 or Class 300 | Treating the class number as a direct psi limit | Check the pressure-temperature table for the body material |
| PN16 or PN40 | Ignoring temperature, flange standard, or material | Match PN with line temperature, flange drilling, gasket, and datasheet |
| WCB, CF8M, WC9 | Approving material from the body mark only | Check the MTC, material standard, medium, and temperature range |
| Flow arrow | Installing the valve like a bidirectional shut-off valve | Confirm line flow direction before installing check, globe, control, or reducing valves |
| Plant tag number | Using the tag as proof of valve specification | Use the tag to find the line list, then compare physical markings and documents |
| Worn or painted body marks | Guessing the missing letters or numbers | Ask for more photos, nameplate data, old purchase records, or inspection documents |
The best inspection habit is to compare at least three sources: the physical valve marking, the product or project document, and the actual line condition. If one source disagrees with the others, resolve that gap before installation.
Need Help Checking Valve Markings Before Replacement?
If a valve marking is clear, use it to start the replacement check. If it is worn, painted over, partly hidden, or different from the line record, do not guess the missing code. Ask for more photos, the old datasheet, the purchase record, or the inspection document before approving the valve.
MacoTango can help compare valve body markings, nameplate data, pressure rating, material code, end connection, and service conditions before you choose a replacement. Send the valve photos, line medium, working pressure, temperature, and required standard to contact our engineers for a practical check.