An EN 1092 PN25 flange will form a reliable valve connection only when the complete interface matches. Check the DN, applicable part of EN 1092, flange outside diameter, pitch circle diameter, number and diameter of bolt holes, facing, gasket, bolting, material, and pressure-temperature limits.
For example, a common DN150 EN 1092-1 PN25 steel flange has a 300 mm outside diameter, a 250 mm bolt circle, and eight 26 mm holes for M24 bolting. Those dimensions help confirm the drilling, but they do not confirm the facing, flange type, thickness, gasket, or valve face-to-face length.
This distinction matters in water and wastewater projects. EN 1092-1 covers steel flanges, while many ductile-iron valves use EN 1092-2 flanges. Their mating dimensions are intended to be compatible for corresponding DN and PN designations, but the joint still needs an approved facing and gasket arrangement.
What does EN 1092-1 PN25 specify?
EN 1092-1 covers circular steel flanges for pipes, valves, fittings, and accessories. It includes PN designations from PN2.5 to PN400 and nominal sizes from DN10 to DN4000, although not every flange type is available in every DN and PN combination.
The standard addresses:
- Flange and collar types
- Mating dimensions and tolerances
- Bolt-hole dimensions and nominal bolt sizes
- Flange facings and jointing-face finish
- Materials and manufacturing methods
- Marking and inspection
- Pressure-temperature ratings
The project specification should identify the adopted edition. A complete designation also states the flange type, facing, DN, PN, and material. Writing only “EN1092 PN25 flange” leaves several purchasing decisions unresolved.
EN 1092-1 versus EN 1092-2 for valves
The part number follows the flange material family:
| Standard part | Main flange material | Typical use around valves |
|---|---|---|
| EN 1092-1 | Steel | Carbon-steel or stainless-steel pipe flanges, fabricated spools, steel valve bodies, and equipment connections |
| EN 1092-2 | Ductile, grey, or malleable cast iron | Ductile-iron gate valves, butterfly valves, check valves, fittings, and waterworks equipment |
| EN 1092-3 | Copper alloy | Selected copper-alloy piping and equipment |
| EN 1092-4 | Aluminium alloy | Selected aluminium-alloy systems |
A steel pipe flange marked EN 1092-1 PN25 may mate with a ductile-iron valve flange made to EN 1092-2 PN25 when the corresponding mating dimensions and facing arrangement are compatible. Do not change the valve flange callout to EN 1092-1 merely because the connecting pipe is steel.
For more detail on the pressure designation itself, see PN25 pressure rating explained.
What does PN25 mean, and what does it not mean?
PN25 is a nominal pressure designation used with the applicable component standard. It is not a promise that every PN25 flange, valve, gasket, or bolted joint can operate at 25 bar under every condition.
The allowable pressure depends on the flange material, flange type, design, temperature, gasketed-joint calculation, and applicable product standard. A pipeline also has to withstand static head, pump shut-off pressure, surge pressure, and the specified hydrostatic test pressure.
The assembled system is limited by its lowest-rated component. Installing a PN25 valve between PN16 pipe flanges does not convert the line to PN25. Our PN10 vs PN16 vs PN25 valve selection guide explains how the pressure classes affect the wider valve specification.
PN25 is approximately 362.6 psi as a unit conversion, but that number is not an ASME Class rating and does not establish flange compatibility. See the separate PN16 and PN25 pressure conversion guide when a datasheet uses both bar and psi.
PN25 flange dimensions and bolt-hole reference
Five dimensions control the basic drilling match:
- DN: nominal connection size
- D: flange outside diameter
- K: pitch circle diameter, also called PCD or bolt-circle diameter
- L: bolt-hole diameter
- n: number of bolt holes
The table below gives common EN 1092-1 PN25 mating and drilling dimensions from DN15 to DN600. All dimensions are in millimetres.
| DN | Flange OD D | Bolt circle K | Bolt holes n x L | Nominal bolt size |
|---|---|---|---|---|
| 15 | 95 | 65 | 4 x 14 | M12 |
| 20 | 105 | 75 | 4 x 14 | M12 |
| 25 | 115 | 85 | 4 x 14 | M12 |
| 32 | 140 | 100 | 4 x 18 | M16 |
| 40 | 150 | 110 | 4 x 18 | M16 |
| 50 | 165 | 125 | 4 x 18 | M16 |
| 65 | 185 | 145 | 8 x 18 | M16 |
| 80 | 200 | 160 | 8 x 18 | M16 |
| 100 | 235 | 190 | 8 x 22 | M20 |
| 125 | 270 | 220 | 8 x 26 | M24 |
| 150 | 300 | 250 | 8 x 26 | M24 |
| 200 | 360 | 310 | 12 x 26 | M24 |
| 250 | 425 | 370 | 12 x 30 | M27 |
| 300 | 485 | 430 | 16 x 30 | M27 |
| 350 | 555 | 490 | 16 x 33 | M30 |
| 400 | 620 | 550 | 16 x 36 | M33 |
| 450 | 670 | 600 | 20 x 36 | M33 |
| 500 | 730 | 660 | 20 x 36 | M33 |
| 600 | 845 | 770 | 20 x 39 | M36 |
Use this table for enquiry review and preliminary field checks. Release fabrication only against the project-adopted standard and the approved drawings for the offered valve, flange, and mating spool.
Why flange thickness is not included in one universal table
Outside diameter and drilling are mating dimensions shared by compatible flange types within the same DN and PN combination. Thickness, bore, hub diameter, neck length, and weld preparation depend on the flange type.
A DN200 PN25 Type 01 plate flange, Type 05 blind flange, Type 11 weld-neck flange, and Type 21 integral valve flange do not use one common thickness. A supplier should state the selected type and provide its complete dimensional drawing.
Bolt length also changes with flange thickness, gasket thickness, washers, nut arrangement, and whether the joint uses bolts or studs. The M size in the table is a nominal bolting reference, not a finished bolt schedule.
Flange types that appear in valve projects
EN 1092-1 uses numbered type identifiers. Type 37 is an identifier, not proof that the standard contains 37 consecutive flange types.
The following types are common around valves and pipeline equipment:
| Type | Description | Typical location |
|---|---|---|
| 01 | Plate flange for welding | Fabricated steel water-pipeline spools and general service |
| 05 | Blind flange | Temporary or permanent line closure, testing, and future branches |
| 11 | Weld-neck flange | Higher-load steel piping and services requiring a butt-welded neck |
| 12 | Hubbed slip-on flange for welding | Selected steel piping systems where the specified type is permitted |
| 13 | Hubbed threaded flange | Selected threaded services subject to project limits |
| 21 | Integral flange | Valve, fitting, vessel, or equipment body manufactured with the flange |
Loose flange and collar combinations also exist. They must be ordered as a compatible assembly because the loose flange alone does not define the process-contact material, bore, collar, or weld end.
The standard’s published pressure-temperature ratings apply to Types 05, 11, 12, 13, and 21 through DN600. For other flange types, the allowable pressure-temperature rating has to be agreed between the equipment manufacturer and purchaser. This is one reason a Type 01 plate flange should not be approved from its PN25 drilling alone.
For a ductile-iron water valve, the integral flange is normally specified to EN 1092-2 rather than EN 1092-1. This is common on products such as flanged gate valves, butterfly valves, and swing check valves.
Flange facing controls the PN25 gasket choice
Matching D, K, n, and L only proves that the bolt pattern is likely to align. The flange facing decides where the gasket sits and how the bolt load reaches it.
| EN facing | Jointing face | Gasket approach |
|---|---|---|
| A | Flat face | Full-face or approved flat gasket arrangement, often used where a steel flange mates with cast or ductile iron equipment |
| B1 | Raised face with standard surface finish | Inside-bolt-circle flat ring gasket or another gasket approved for the service and finish |
| B2 | Raised face with a smoother specified finish | Gasket selected for the smoother surface, often an engineered or metallic gasket arrangement |
| C and D | Tongue and groove | Matched tongue and groove faces with the specified confined gasket |
| E and F | Spigot and recess | Matched spigot and recess faces with the specified gasket |
| G and H | O-ring spigot and O-ring groove | Matched faces with the correct O-ring dimensions and material |
B1 and B2 are both raised faces. The main distinction is the specified jointing-face surface roughness, not a simple rule that B2 is a deeper PN25 face. State the facing on the purchase order and drawing.
Full-face versus inside-bolt-circle gaskets
A full-face gasket extends across the flange face and has holes for the bolts. It can help distribute the clamping load across a flat-faced cast or ductile-iron flange.
An inside-bolt-circle gasket, sometimes called an IBC or ring gasket, sits inside the bolt circle. It is common with raised-face steel flanges because the raised face concentrates the gasket load over a smaller sealing area.
These gasket forms are not automatic substitutes for each other. Connecting a raised-face steel flange directly to a flat-faced iron valve can impose unwanted bending stress on the iron flange. Use matching flat faces or an arrangement approved by the valve manufacturer and piping engineer, usually with the correct full-face gasket where applicable.
How to select a PN25 gasket
EN 1514 provides dimensional standards for gaskets used with PN-designated flanges. EN 1514-1 covers non-metallic flat gaskets with or without inserts, while EN 1514-2 covers spiral-wound gaskets for steel flanges. The dimensional standard does not select the gasket material for the process.
Check these five items before approving a PN25 gasket:
- Confirm the flange standard, DN, PN, and facing on both sides.
- Match the gasket form to the faces: full face, IBC ring, spiral wound, confined gasket, or O-ring.
- Check fluid compatibility, including cleaning chemicals and occasional contamination.
- Check minimum and maximum temperature, continuous pressure, surge pressure, and test conditions.
- Confirm gasket thickness, compressibility, surface-finish requirement, storage life, approvals, and the joint-tightening procedure.
Common gasket materials for valve connections
| Gasket material or construction | Typical use | Main checks before approval |
|---|---|---|
| EPDM | Potable water, treated water, and many wastewater services | Drinking-water approval where required, temperature, disinfectant concentration, and no hydrocarbon exposure |
| NBR | Water containing oil or grease and selected wastewater duties | Oil concentration, temperature, potable-water restrictions, and chemical compatibility |
| Compressed non-asbestos fibre | General industrial water and selected process duties | Binder chemistry, pressure-temperature capability, flange finish, and fluid compatibility |
| PTFE or filled PTFE | Corrosive chemical service | Creep, cold flow, gasket stress, temperature, and flange rigidity |
| Spiral wound | Raised-face steel flanges in higher-temperature or demanding process service | EN 1514-2 dimensions, winding and filler materials, inner and outer rings, face finish, and required seating stress |
For a PN25 drinking-water valve, an approved EPDM gasket is common, but it still needs the correct dimensions and facing. For a raised-face steel process flange, a spiral-wound gasket may be more suitable. The words “PN25 gasket” do not define either choice.
Valve flange compatibility: a seven-step check
1. Identify the valve-body material and correct EN 1092 part
A carbon-steel valve may use EN 1092-1 integral flanges. A ductile-iron valve normally uses EN 1092-2. Record the part number instead of shortening both to “EN flange.”
2. Compare the approved mating dimensions
Compare D, K, n, and L on the valve drawing with the mating pipe-flange drawing. Do not rely on the DN and PN markings alone.
Corresponding EN 1092 parts are intended to provide compatible mating dimensions for suitable flange types. Minor differences in stated hole clearance or manufacturing tolerance can still appear between material parts, so use the nominal bolt size and both approved drawings.
3. Match the flange faces
Confirm flat face, B1, B2, or another specified paired facing. Check the raised-face diameter, height, surface condition, coating limits, and gasket seating width.
Paint, fusion-bonded epoxy, rust, weld spatter, or handling damage on the sealing face can cause leakage even when the drilling is correct.
4. Approve the gasket as part of the joint
Check the gasket standard, form, material, dimensions, thickness, approvals, and storage condition. A gasket left in sunlight or contaminated with oil may no longer perform as specified.
5. Select the complete bolting set
Confirm bolt or stud diameter, grade, length, thread engagement, nuts, washers, corrosion protection, and lubricant. Galvanizing, anti-seize compound, and thread condition change the relationship between tightening torque and bolt tension.
This is why a universal PN25 torque value is unreliable. The approved procedure should account for the bolt material, gasket, friction condition, flange material, and allowable gasket stress.
6. Check the valve dimensions beyond the flange
Flange compatibility does not confirm that the valve fits the available space. Verify face-to-face length, body clearance, handwheel or gearbox access, actuator envelope, flow direction, and maintenance removal space.
For replacement check valves, the H44X swing check valve dimensions guide shows why flange drilling and face-to-face length need separate checks.
7. Confirm the pressure-temperature envelope
Review normal operating pressure, maximum static pressure, pump shut-off pressure, surge pressure, test pressure, and minimum and maximum temperature. Confirm the valve, pipe flange, gasket, bolting, and adjacent equipment against the same design case.
Compatibility matrix for common project combinations
| Proposed connection | Bolt-up expectation | Required decision |
|---|---|---|
| EN 1092-1 PN25 steel flange to EN 1092-1 PN25 steel flange, same DN | Normally compatible when the mating dimensions and flange types correspond | Confirm facing, gasket, bore, material, p/T rating, and bolting |
| EN 1092-1 PN25 steel pipe flange to EN 1092-2 PN25 ductile-iron valve flange, same DN | Corresponding mating dimensions are intended to be compatible | Confirm flat or raised faces, gasket form, joint loading, and manufacturer approval |
| PN25 valve to PN16 pipeline flange | Do not assume compatibility or adequate rating | Compare drilling and faces, then rate the complete system by the lowest-rated component |
| EN 1092 PN25 to ASME B16.5 Class 150 | Not interchangeable based on pressure comparison | Use a purpose-designed transition or change the mating flange to the specified standard |
| EN 1092 PN25 to JIS, GOST, or legacy BS/DIN flange | Not interchangeable based on DN alone | Compare the exact dimensional tables and project-approved transition detail |
| Wafer or lug valve between EN 1092-1 PN25 flanges | Possible only when the valve is designed for the exact flange set | Check bore clearance, disc swing, liner or gasket function, bolt length, lug engagement, and dead-end rating |
ASME Class 150 is often compared with PN16, PN20, or PN25 in commercial discussions. These are pressure comparisons, not drilling conversions. Never slot holes, reduce bolt diameter, or force misaligned pipework to make two standards fit.
Special checks for gate, butterfly, and check valves
Flanged gate valves
Confirm the integral valve flange standard, face-to-face series, stem and handwheel clearance, and full-bore dimensions. A flanged soft seal gate valve for a ductile-iron water line may be PN25 while its flange callout remains EN 1092-2.
Flanged butterfly valves
Check the flange inside diameter against the valve seat and disc envelope. A bolt pattern can align while the pipe flange bore prevents the disc from opening fully. Also check whether the elastomer liner acts as the flange seal or requires a separate gasket.
Wafer and lug butterfly valves
Verify that the valve body is approved for installation between EN 1092-1 PN25 flanges. Confirm through-bolt length for wafer designs and thread engagement for lug designs. Dead-end service requires a separate rating check.
Swing and dual-plate check valves
Check disc clearance, installation orientation, hinge-pin access, and face-to-face length. For a wafer dual-plate valve, confirm that the flange bore and gasket do not obstruct disc travel.
Dismantling joints beside valves
A dismantling joint can provide axial adjustment and removal space, but it does not correct the wrong drilling standard or an incompatible flange face. Specify the same DN, PN, flange standard, and facing for the complete assembly. See the dismantling joint installation and selection guide for layout details.
Installation practices that protect the flange joint
- Inspect both flange faces, bolt holes, gasket, and bolting before assembly.
- Align the pipe and valve without using flange bolts to pull the line into position.
- Support the valve independently when its weight or actuator load can strain the pipe.
- Centre the gasket without using adhesive or grease unless the approved procedure permits it.
- Install clean bolting with the specified washers, coating, and lubricant.
- Tighten in a cross pattern through several controlled passes.
- Use the project-approved torque or tension procedure rather than a generic PN25 chart.
- Complete the specified leak or hydrostatic test and record the result.
Uneven tightening can rotate the gasket, overload one side of a cast flange, or leave part of the sealing surface below the required seating stress. Pipe misalignment creates a different problem: the joint may pass an initial test and leak after temperature, vibration, or pressure cycling changes the external load.
Common EN1092 valve flange mistakes
Ordering by DN and PN only
“DN200 PN25 valve” does not identify the flange part, facing, drilling details, face-to-face series, or gasket.
Using one thickness for every flange type
Type 01, Type 05, Type 11, and Type 21 have different constructions. Shared bolt drilling does not make their thicknesses identical.
Treating B1 and B2 as different pressure classes
Both are raised-face finishes. The required finish follows the gasket and project specification, not a shortcut based on PN25 alone.
Fitting a ring gasket between flat-faced iron flanges without approval
This concentrates the bolt load near the bore and can bend or damage the flange. Use the approved full-face arrangement where required.
Assuming a PN25 valve upgrades a PN16 line
The pipe flange, fitting, gasket, bolts, and connected equipment remain PN16 unless separately replaced and verified.
Modifying bolt holes on site
Slotted, flame-cut, or enlarged holes change load distribution and remove the dimensional control provided by the standard. Use a designed transition piece.
Copying an ASME torque table
Torque depends on the actual metric bolting, coating, lubricant, gasket, face finish, and joint calculation. A similar nominal pipe size does not make the table applicable.
How to specify an EN 1092 PN25 valve connection
A useful purchase description identifies the valve and both sides of the joint. For example:
DN200 PN25 resilient-seated gate valve for treated water, ductile-iron body, flanged ends to EN 1092-2 PN25, flat face, approved EPDM full-face gasket to EN 1514-1, mating carbon-steel pipe flanges to EN 1092-1 PN25 Type 01 Form A, face-to-face dimension to the stated EN 558 series, maximum continuous pressure 18 bar, maximum surge pressure 23 bar, temperature 5 to 45 degrees C, fusion-bonded epoxy coating, complete bolting schedule, dimensional drawing, material certificates, and pressure test report required for approval.
The values above are an example format, not a universal valve specification. Replace them with the project design conditions.
Include the following documents with the technical submittal:
- Valve general arrangement drawing
- Flange detail showing D, K, n, L, face, and thickness
- Mating pipe-flange drawing and material
- Valve face-to-face dimension and applicable series
- Gasket datasheet and dimensional standard
- Bolting grade, coating, length, and tightening procedure
- Pressure-temperature data for the offered materials
- Coating and potable-water approvals where required
- Material certificates and valve pressure-test report
Norite’s industrial pump and valve range includes gate, butterfly, check, control, and air valves for PN-rated water systems.
Frequently asked questions
Is EN 1092-1 PN25 the same as DIN PN25?
EN 1092-1 replaced or incorporated many older DIN-based flange practices, but an old DIN callout should not be converted by name alone. Check the exact legacy DIN standard, DN, dimensions, facing, and project acceptance against the required EN 1092-1 edition.
Are EN 1092-1 and EN 1092-2 PN25 flanges compatible?
Their corresponding mating dimensions are intended to be compatible for suitable flange types with the same DN and PN. EN 1092-1 applies to steel, while EN 1092-2 applies to cast iron materials. The facing, gasket, bolt loading, material limits, and manufacturer approval still need review.
Can a PN25 valve connect to PN16 flanges?
Only after a full dimensional and pressure-rating review. Some DN and standard combinations may share selected drilling dimensions, while others do not. Even if the bolts align, the complete line remains limited by the PN16 components.
Is PN25 equivalent to ASME Class 150?
No. A pressure comparison does not make the standards equivalent. EN 1092-1 and ASME B16.5 use different designation systems, dimensional tables, flange faces, and pressure-temperature rules.
Which gasket should be used for an EN 1092-1 PN25 flange?
Choose the gasket from the flange faces, fluid, temperature, pressure, surface finish, and bolting calculation. A flat-face waterworks joint may use an approved EPDM full-face gasket. A raised-face steel process joint may use an IBC flat gasket or an EN 1514-2 spiral-wound gasket, depending on the service.
Are PN25 bolt sizes the same for all DN sizes?
No. Bolt diameter and quantity increase through the DN range. For example, DN50 commonly uses four M16 bolts, DN150 uses eight M24 bolts, and DN300 uses sixteen M27 bolts under the EN 1092-1 PN25 drilling shown above.
Does matching the bolt circle prove valve compatibility?
No. Also check the hole diameter, flange face, gasket, bore, flange thickness, bolt length, valve face-to-face dimension, disc clearance, pressure-temperature rating, and body material.
Send a complete PN25 flange enquiry
For a valve quotation, send the valve type, DN, quantity, body material, operating pressure, surge pressure, test pressure, temperature, fluid, EN 1092 part, facing, mating-flange drawing, gasket requirement, face-to-face series, actuator details, and required certification.
Contact Norite to review an EN 1092-1 or EN 1092-2 PN25 valve connection before the valve and pipe spools are released for production.
