Selecting valves for an industrial project involves much more than choosing the valve type and size. Two DN100 ball valves may have the same nominal size, but differences in pressure rating, connection type, material specification, or installation dimensions can prevent them from meeting the design requirements or fitting the existing pipeline.
This guide explains the key elements of a Valve Specification, including pressure ratings, connection types, dimensions, materials, applicable standards, and other technical parameters. It also uses specification sheets and practical engineering examples to show how to read a Valve Specification correctly and avoid common mistakes during valve selection and procurement.
1. What Is a Valve Specification?
The following sections introduce the basic concept of a Valve Specification and its main components.
1) Definition of a Valve Specification
A Valve Specification is a set of technical parameters that defines the requirements of a valve, including valve type, size, pressure rating, connection type, materials, operating method, and applicable standards. It determines whether the valve is suitable for the design conditions and serves as the technical basis for procurement, manufacturing, inspection, and installation.
2) What Does a Complete Valve Specification Include?
A complete Valve Specification typically includes the following information:
| Parameter | Example |
| Valve Type | Ball Valve |
| Size | DN100 (NPS 4) |
| Pressure Rating | Class 300 |
| Connection | RF Flanged |
| Body Material | ASTM A216 WCB |
| Seat Material | PTFE |
| Operation | Manual |
| Design Standard | API 608 |
| Test Standard | API 598 |
For oil & gas, chemical, and power generation projects, the specification may also include additional requirements such as fire-safe design, anti-static protection, NACE compliance, anti-corrosion coatings, third-party inspection, and certification.
Valve Specification Example
2. Valve Pressure Ratings
The pressure rating defines the maximum allowable working pressure of a valve at a specified temperature. It is one of the most critical parameters in a Valve Specification.
Valve Pressure Ratings
1) Difference Between PN and Class
Industrial valves mainly use two pressure rating systems: PN (Pressure Nominal) and ASME Class. PN belongs to the European standards system, while Class follows the American standards system.
PN (Pressure Nominal): Used primarily in EN, DIN, ISO, and related GB and HG/T standards. Common ratings include PN10, PN16, PN25, PN40, PN63, and PN100.
Class (Pressure Rating): Used primarily in ASME and API standards. Common ratings include Class 150, 300, 600, 900, 1500, and 2500.
The key point is that PN and Class belong to different pressure and dimensional systems. Their rating numbers are not directly interchangeable.
Under both systems, the allowable working pressure depends on the valve material and operating temperature. Always verify the pressure-temperature ratings in the applicable standard during valve selection.
| ASME Class | Pressure at 38°C (MPa) | Approximate Metric Equivalent | Typical Applications |
| Class 150 | 2.0 | Often compared with PN16, but not interchangeable | Cooling water, low-pressure air, ambient-temperature oil |
| Class 300 | 5.17 | Approximately between PN40 and PN63 | Medium-pressure steam and general chemical process piping |
| Class 600 | 10.34 | Often referenced against PN100, but not directly equivalent | High-pressure crude oil and gas pipelines |
| Class 900 | 15.51 | Often referenced against PN160, but not directly equivalent | High-pressure synthesis and natural gas transmission systems |
| Class 1500 | 25.86 | Often referenced against PN260, but not directly equivalent | Ultra-high-pressure hydrogenation service |
2) Working Pressure, Design Pressure, and Test Pressure
A valve specification normally defines three different pressure values:
- Working Pressure: The actual operating pressure during continuous service.
- Design Pressure: The maximum pressure considered during design. It is typically higher than the working pressure.
- Test Pressure: The pressure applied during factory hydrostatic strength and seat leakage tests.
For example, a ball valve may have a working pressure of 10 bar, a design pressure of 16 bar, and a shell test pressure of 24 bar. This does not mean the valve can operate continuously at 24 bar. The test pressure is used only to verify the strength of the valve body and the sealing performance.
For systems subject to water hammer, pressure fluctuations, or frequent cycling, engineers normally select a higher pressure class than the actual working pressure to provide adequate long-term reliability.
3) Pressure-Temperature Ratings
The allowable working pressure of a valve depends not only on its pressure class but also on the operating temperature. As temperature increases, material strength decreases, reducing the maximum allowable working pressure. Therefore, the same pressure class does not provide the same pressure capacity at all temperatures.
For example, an ASTM A216 WCB valve with an ASME B16.34 Class 150 pressure rating has the following allowable pressures:
- At 38°C: 2.0 MPa
- At 200°C: 1.6 MPa
- At 343°C: 1.2 MPa
3. Valve Connection Types
The connection type defines how the valve connects to the piping system. It affects not only installation efficiency but also sealing performance, pressure capacity, and future maintenance. During procurement, even if the valve size and pressure rating are correct, incompatible connection standards can prevent installation.
1) Threaded Connections (NPT, BSPT, BSPP)
Threaded connections are commonly used on small-diameter, low-pressure utility piping operating at ambient temperature. The three most common thread types are:
- NPT (National Pipe Taper): Uses tapered threads to create the primary seal. Installers normally apply a suitable thread sealant during assembly. This connection is widely used in instrument tubing and small utility systems.
- BSPT (British Standard Pipe Taper): Common in European standards. It is typically used for PN16 and lower pressure applications, including water supply, drainage, and compressed air systems.
- BSPP (British Standard Pipe Parallel): Provides only the mechanical connection. The threads do not normally provide sealing and must be used with a gasket, O-ring, or another sealing element.
NPT and BSP threads are not interchangeable. Although their dimensions are similar, they use different thread forms and thread angles. Forcing them together often causes leakage.
Threaded valves are not recommended for service above 200°C, piping subjected to continuous vibration, or lines carrying flammable or explosive media, because long-term operation may loosen the threaded connection and result in leakage.
Threaded Connection
2) Flanged Connections
Flanged connections are the most common connection type for industrial valves. Typical flange standards include ASME B16.5, EN 1092-1, and JIS B2220. These standards differ in bolt-hole quantity, bolt-circle diameter, and sealing-face dimensions. Even with the same nominal size, flanges from different standards are not directly interchangeable.
The main flange types and their typical applications are:
- RF (Raised Face): The most widely used flange type. It is suitable for most ambient-temperature, low- and medium-pressure process piping, provides good versatility, and is easy to assemble and disassemble.
- RTJ (Ring Type Joint): Uses a metallic ring gasket for sealing. It is designed for high-temperature, high-pressure, toxic, flammable, and explosive service. RTJ flanges are typically used with Class 600 and higher pressure ratings and provide excellent resistance to temperature cycling.
- FF (Flat Face): Commonly used on cast iron and ductile iron valves and water supply equipment. Before installation, verify that the mating flange has the same sealing face. Do not connect FF and RF flanges without confirming compatibility.
Three Flange Face Types
3) Welded Connections (Socket Weld & Butt Weld)
Welded connections provide the highest sealing integrity and the best vibration resistance. They are generally divided into Socket Weld (SW) and Butt Weld (BW).
- SW (Socket Weld): Suitable for DN15–DN50 high-pressure piping. It provides high weld strength and is relatively easy to install. However, liquid can collect inside the socket, so this connection is not recommended for corrosive media.
- BW (Butt Weld): Suitable for DN50 and larger pipelines. It provides a full-penetration welded joint with no dead space, excellent pressure resistance, and high vibration resistance. It is the preferred connection for toxic, high-temperature, and high-pressure service. However, maintenance requires cutting the pipeline, making it unsuitable for systems requiring frequent valve removal.
Socket Weld and Butt Weld
4) Press-Fit, Grooved, and Other Connection Types
- Press-Fit Connection: Commonly used in stainless steel potable water systems and low-pressure HVAC piping. It offers fast installation without welding and is generally suitable for PN10 and PN16 ambient-temperature service.
- Grooved Connection: Widely used in fire protection systems and large-diameter water supply and drainage piping. It allows rapid installation and provides good seismic performance. Most products are intended for PN16 and lower pressure service and are not suitable for high-temperature or corrosive media.
- Wafer / Lug Connection: Commonly used on butterfly valves. Wafer-type valves are clamped between two flanges, while lug-type valves have threaded lugs that can support removal of one side of the pipeline when the design permits.
4. Valve Dimensions
Valve dimensions affect not only flow capacity but also compatibility with existing piping and equipment. In practical engineering, selection involves more than nominal size. Installation dimensions, flow passage size, and installation clearance must also be verified.
1) Difference Between DN, NPS, and Inch
DN (Diameter Nominal) and NPS (Nominal Pipe Size) are both nominal sizes. Neither value represents the actual internal diameter of the valve.
- DN: Commonly used in ISO, EN, and DIN standards, such as DN50 and DN100.
- NPS: Commonly used in ASME and API standards, such as NPS 2 and NPS 4.
- Inch: The imperial unit normally used to express an NPS size.
For example, DN15, DN25, DN50, and DN100 correspond to NPS 1/2, NPS 1, NPS 2, and NPS 4, commonly referred to as 1/2 inch, 1 inch, 2 inches, and 4 inches.
2) Nominal Size and Actual Flow Passage
Different valve types with the same DN may have significantly different internal flow passages.
For example, a Full Port ball valve has a bore close to the internal diameter of the connected pipe and therefore produces less pressure loss. A Reduced Port ball valve has a smaller bore. It costs less, but it increases flow resistance.
For piping systems that require full flow capacity, low pressure drop, or pigging, engineers normally specify a Full Port valve. For general water supply, drainage, or HVAC systems, a Reduced Port valve may be selected based on cost and service conditions.
3) Face-to-Face, End-to-End, and Other Installation Dimensions
In addition to DN and pressure rating, installation dimensions must be confirmed during procurement.
The most common dimensions include:
- Face-to-Face (F-F): The installation length between the sealing faces of a flanged valve.
- End-to-End (E-E): The installation length between the ends of a welded or threaded valve.
- Center-to-End (C-E): The installation dimension used for certain angle valves, globe valves, and similar products.
These dimensions normally follow standards such as ASME B16.10, EN 558, and ISO 5752. Even when two valves have the same DN, pressure rating, and connection type, different installation lengths may prevent direct replacement.
4) How to Confirm Installation Space Requirements
Insufficient installation space is a common reason for valve replacement failure on site.
In addition to checking the valve length, confirm the following:
- The handle, handwheel, or actuator has enough operating clearance.
- The electric or pneumatic actuator will not interfere with adjacent equipment.
- Adequate space is available for disassembly, maintenance, and replacement.
- Pipe supports and flange locations meet the installation requirements.
For retrofit projects, verify the valve against the equipment layout and overall dimension drawing rather than purchasing based only on DN and pressure rating.
5. What Other Parameters Should a Complete Valve Specification Include?
In addition to pressure rating, connection type, and dimensions, a complete Valve Specification should define the materials, operating method, flow characteristics, and applicable standards. These items are often overlooked, but they directly affect valve service life and suitability for the intended duty.
1) Valve Body, Stem, and Sealing Materials
Select valve materials based on the process medium, operating temperature, and corrosive environment.
Examples include:
- WCB: Commonly used for water, steam, oil, and other industrial media compatible with carbon steel.
- CF8 / CF8M (304 / 316 Stainless Steel): Cast equivalents of 304 and 316 stainless steel, respectively. They are commonly used where improved corrosion resistance is required.
- A105 Forged Steel: Commonly used for small-bore forged steel valves in high-pressure service or applications with significant temperature variation.
Sealing materials are equally important. PTFE provides good corrosion resistance and suits most chemical media. EPDM is more suitable for water systems. High-temperature steam systems may require metal seats or graphite seals. In engineering procurement, confirming only the body material while ignoring the sealing material is a common mistake.
2) Operating Method (Manual, Electric, Pneumatic)
Depending on the control requirements, a valve may use:
- Manual: Operated by a handle or handwheel. The design is simple and relatively low-cost.
- Electric: Suitable for remote operation and automated systems.
- Pneumatic: Provides fast actuation and is widely used in industrial automation.
- Hydraulic: Suitable for large-diameter valves or high-torque applications.
When selecting the actuation method, also consider the available power supply, instrument air, control system, and site maintenance conditions.
3) Flow Direction and Cv/Kv Flow Coefficients
For globe valves, check valves, and similar products, confirm the correct flow direction.
Where flow control is required, also review the Cv or Kv value. These coefficients indicate valve flow capacity and are key parameters for regulating and control valves.
4) Applicable Standards, Test Requirements, and Certifications
The specification should also define the applicable product standards and inspection requirements, for example:
- Design Standards: API, ASME, ISO, EN, DIN
- Pressure Testing: API 598, ISO 5208
- Flange Standards: ASME B16.5, EN 1092-1
- Material Standards: ASTM, EN
Depending on the target market and industry requirements, the valve may also require potable-water compliance such as ACS, WRAS, or NSF; EU pressure equipment conformity documents such as PED-related CE documentation; or an API Monogram license for specific API product standards. Third-party inspection requirements should separately define the inspection agency, scope, and witness points.
Appendix: Standardized Valve Specification Checklist (For Reference)
| Review Category | Key Review Items | Compliance Requirements |
| Pressure Specification | Pressure rating, pressure-temperature suitability, test standard | Match the design pressure and temperature, provide an adequate safety margin, and identify the applicable standard |
| Dimensional Specification | DN/NPS, full/reduced port, face-to-face standard | Clearly define the bore type and ensure the face-to-face dimension complies with the project standard |
| Connection Specification | Connection type, flange standard, sealing face, compatible wall thickness | Fully match the piping standard and avoid mixed or incompatible connections |
| Material Specification | Body, stem, sealing materials, and special corrosion protection | Match the process medium, temperature, and corrosive conditions |
| Performance Specification | Leakage class, Cv/Kv, flow direction, pigging requirement | Meet process flow, sealing, operation, and maintenance requirements |
| Actuation Specification | Operating method, fail position, enclosure rating | Match automation, hazardous-area, and interlock requirements |
| Standards and Certification | Manufacturing standard, test standard, special certifications | Ensure traceable parameters and compliance with project requirements |
6. How to Read a Valve Specification Sheet
Manufacturers may use different specification sheet formats, but the core parameters remain largely the same. Once you understand the key fields, you can quickly determine whether a valve meets the project requirements. The following examples use typical valve specification data to explain how to interpret the main parameters.
Case 1:
Valve Specification Sheet 1
1) Product Specifications
a) Wedge: Ductile-Iron Wedge, EPDM Encapsulated → The wedge uses a ductile iron core fully encapsulated in EPDM rubber.
b) Stem Seal: Triple O-Ring Stem Seal → The stem uses three O-rings for sealing.
c) Face-to-Face: ANSI / ASME B16.10, EN 558 → These standards define the valve installation length.
d) Flange Drilling: ANSI B16.1, ASME B16.42 → These standards define the flange dimensions, bolt-hole spacing, and bolt-hole arrangement.
e) End Connection: Grooved Ends to AWWA C606 → This product series is available with flanged ends or grooved ends complying with AWWA C606.
f) Certification: UL / ULC Listed, FM Approved → The product carries fire-protection certifications and may be used in fire systems that require these approvals.
2) Corrosion Protection
a) Coating: Fusion Bonded Epoxy (FBE) → The valve body receives a fusion-bonded epoxy coating on both internal and external surfaces.
b) Standard: AWWA C550 → The anti-corrosion coating complies with this standard.
3) Options
a) Stem Material: Copper alloy or 316 stainless steel stem available.
b) Fasteners: A2-70 (304) or A4-70 (316) stainless steel fasteners available.
c) Wedge Material: EPDM- or NBR-encapsulated wedge available.
d) Operation: Handwheel or operating nut available.
4) Material Specifications
a) Body: ASTM A536 Grade 65-45-12, indicating a ductile iron valve body.
b) Wedge: EPDM Fully Encapsulated Ductile Iron, indicating a ductile iron wedge fully encapsulated in EPDM rubber to provide soft sealing.
c) Stem: ASTM A276 Type 304, indicating a 304 stainless steel stem.
d) Body/Bonnet Gasket: D2000 EPDM, indicating an EPDM rubber seal between the valve body and bonnet.
e) ASTM Specification: Each material corresponds to a specific ASTM standard.
5) Schematic
a) Product View: Shows the valve appearance and operating arrangement.
b) Section View: Shows the internal structure and sealing arrangement.
c) L: Valve face-to-face dimension.
d) H: Overall valve height.
e) D: Outside diameter of the handwheel or operating component.
6) Main Dimensions
a) Size: Nominal valve size in inches.
b) L: Valve installation length.
c) H: Overall valve height.
d) D: Handwheel diameter.
e) Unit: Dimensions are provided in both millimetres and inches.
For example, the 4-inch model has an installation length L of 229 mm, an overall height H of 361 mm, and a handwheel diameter D of 305 mm. These values allow engineers to verify installation clearance and pipeline compatibility.
Case 2:
Valve Specification Sheet 2
1) Materials
The material table shows that the body and bonnet use bronze complying with IS 318 Gr. LTB 2. The ball uses either ASTM A276 Type 304 stainless steel bar or ASTM A351 Gr. CF8 cast stainless steel. The body seat rings, thrust washer, and gland packing use PTFE. The stem uses stainless steel complying with ASTM A276 Type 410. The gland uses forged brass, while the lever and nut use carbon steel.
2) Sectional View
The sectional view on the right shows how the internal ball valve components fit together. The numbered callouts correspond directly to the item numbers in the material table on the left. For example, item 1 identifies the body, item 3 the ball, item 4 the body seat ring, item 7 the stem, and item 9 the lever.
The dimension letters correspond to the dimension table below: A indicates the overall end-to-end length, B the threaded connection size, C the height from the valve centerline to the top, and D the lever length.
3) Sizes / Dimensions
The first column lists the sizes in inches, and the second column gives the corresponding nominal diameters. For example, 1/2 inch corresponds to DN15, 3/4 inch to DN20, 1 inch to DN25, and the largest size, 2 inches, to DN50.
4) Suitable For
The table states that the valve is suitable for Water and Oil.
7. Common Valve Specification Mistakes During Procurement, Case Examples, and Preventive Measures
Mistake 1: Selecting the pressure rating based only on ambient-temperature pressure without considering temperature derating
Case: A heat-transfer oil system was designed for 310°C and 1.5 MPa. The purchaser selected a PN16 carbon steel gate valve. At the operating temperature, the allowable working pressure of the PN16 valve dropped to 1.1 MPa, and the bonnet leaked during long-term operation.
Solution: State both “Design Pressure: 1.5 MPa” and “Design Temperature: 310°C” in the purchase order, and require the manufacturer to verify the rating against the ASME B16.34 pressure-temperature table. If WCB Class 150 does not meet the requirement, upgrade directly to Class 300 instead of selecting the valve only by its ambient-temperature pressure rating.
Mistake 2: Treating DN as the pipe outside diameter and failing to match the pipe Schedule for welded valves
Case: A DN50 BW ball valve was supplied with weld ends prepared for Sch40 pipe, while the site piping used Sch80 heavy-wall pipe. The fit-up gap exceeded the allowable limit, so the valve could not be welded into the line.
Solution: When purchasing a BW ball valve, add “Pipe Schedule: Sch80 (ASTM A106 Gr. B)” to the purchase order and require the manufacturer to machine the weld ends for Sch80 pipe.
Mistake 3: Failing to specify full port or reduced port and accepting a reduced-port valve by default
Case: A natural gas pipeline required pigging. The purchase order specified a DN100 ball valve but did not require a full port. The supplied valve had a reduced bore of only DN80, so the pig could not pass through.
Solution: State “Full Port (Full Bore)” directly in the order and require the manufacturer to provide the Minimum Bore. This prevents the supplier from providing a reduced-port ball valve by default.
Mistake 4: Mismatching the connection type with the service conditions—using a threaded valve on a vibrating pipeline
Case: A DN25 NPT threaded ball valve was installed on a compressor outlet circulation line. After three months of continuous vibration, the threaded joint leaked externally, creating a safety hazard because the line carried a flammable and explosive medium.
Solution: For continuously vibrating lines such as compressor or pump outlets, use SW socket-weld connections for small-bore valves where possible. Where frequent removal is required for maintenance, use RF flanged connections instead of NPT or BSP threaded connections.
8. Conclusion
A Valve Specification is more than a product data sheet. It determines whether the valve can meet the design conditions, fit the pipeline correctly, and operate reliably over the long term. Every parameter—including pressure rating, connection type, dimensional standard, material, sealing arrangement, and applicable standard—can affect project safety, reliability, and future maintenance costs.
For projects requiring industrial valves that comply with API, ASME, EN, DIN, ISO, or other international standards, or where valve selection support is required for specific service conditions, contact Plumberstar. We can help confirm the Valve Specification, recommend a suitable valve solution, and provide complete technical documentation, certification files, and project support.
