Quick summary:
- A complete valve data sheet is the primary technical communication between the specifying engineer and the valve manufacturer — missing or ambiguous information leads to non-conforming deliveries, costly revisions, and valves that are inadequate for their service
- The most common data sheet errors — missing operating conditions, unspecified shutoff class, absent Yoast data, omitted fugitive emission requirements, and undefined SIL requirements — are systematic rather than random and can be eliminated by a structured data sheet review process
- Engineering completeness in a valve data sheet means all information required to specify, manufacture, test, and install the valve is unambiguously defined — not all information that could theoretically appear on a data sheet, which leads to over-specification that drives unnecessary cost
The Valve Data Sheet — Its Purpose and Anatomy
A valve data sheet (VDS) is the primary engineering document that defines a valve specification for procurement. It translates the process engineering requirements (fluid, pressure, temperature, flow rate), the project engineering standards (pressure class, material specification, testing requirements), and the instrumentation and control requirements (actuator type, position feedback, control signal) into a single, unambiguous technical document from which any competent valve manufacturer can produce a compliant quotation and, after approval, a compliant valve.
A valve data sheet typically contains sections covering: service data (process fluid, operating pressure and temperature, design pressure and temperature, flow rate, fluid phase and composition); valve body data (valve type, body pattern, size, pressure class, end connections, body and bonnet material, face-to-face dimension); trim data (trim type, trim material, seat leakage class, flow characteristic for control valves, Cv); actuator data (actuator type, fail-safe action, supply pressure or supply voltage, signal input, manual override provision); instrument data (limit switch type, position transmitter, solenoid valve); testing and inspection (pressure test requirements, NDE, NACE compliance, fire-safe certification, fugitive emission testing); and technical standards (applicable design standards, piping class, project specification reference).
The data sheet is the engineering contract between the specifying engineer and the supplier. Information that is not on the data sheet does not exist from the supplier’s perspective. If the shut-off class is not specified, the supplier will deliver whatever class is easiest to manufacture (typically Class III or IV). If the fugitive emission testing is not specified, the supplier will not provide it. If the SIL certification is not specified, the supplier will not certify to SIL. The engineering discipline of completing the data sheet correctly — every field that applies, filled in correctly — is what converts engineering intent into a deliverable specification.
The Most Common Data Sheet Errors
After reviewing thousands of valve data sheets across process engineering projects, the same errors recur with remarkable consistency. These are not random omissions — they are systematic gaps that reveal the knowledge boundaries of specifying engineers who have not fully understood what information is required to produce a compliant valve. The most frequent:
Missing or incomplete operating conditions: The data sheet shows design pressure and temperature (maximum values) but not normal operating pressure and temperature, minimum operating temperature, and shut-off differential pressure. These are not the same. A valve designed for 100 bar / 300°C may operate normally at 40 bar / 200°C and must shut off against 80 bar differential at -20°C (during winter shutdown). The control valve sizing, the actuator spring rate, and the seat leakage test condition are all determined by the operating conditions, not just the design maximums. Missing operating conditions produces control valves that are incorrectly sized and actuators that cannot operate the valve under the worst-case combination of conditions.
Unspecified seat leakage class: The data sheet says “tight shutoff” without specifying which class (Class II through Class VI per API 598 / FCI 70-2). “Tight shutoff” means different things to different engineers — to some it means Class IV (less than 0.01% of Cv as leakage at test pressure), to others it means Class VI (zero detectable leakage with soft seat). Without a leakage class number, the supplier will select whatever class their standard trim achieves — typically Class IV for metal seats, Class V or VI for soft seats. If the application genuinely requires Class VI — zero leakage for toxic gas isolation or ESD function — a data sheet that doesn’t specify this will not produce a Class VI valve.
Absent minimum flow specification for control valves: Control valve data sheets commonly specify only the design flow rate. The minimum controllable flow — the smallest flow that the valve must control accurately — is equally important for correct valve sizing. A valve sized only for the design flow may be dramatically oversized at minimum flow, where the valve must operate at less than 5% of its total Cv range. This leads to the poor control performance at low loads that is one of the most common complaints about control valve performance in practice.
Missing NACE requirement on sour service valves: The process fluid contains H₂S but the data sheet does not specify NACE MR0175 / ISO 15156 compliance. The supplier delivers a standard valve. On receiving inspection, or during service, the non-compliance is discovered. The valve must be replaced with a compliant one — at full cost, plus the project delay cost of the discovery and replacement. This is an entirely preventable error that requires only awareness of the NACE requirement and a line on the data sheet.
Undefined fugitive emission requirements: No statement of fugitive emission testing standard (ISO 15848-1 Class, API 624) for gate or globe valves in VOC service. The supplier delivers a standard valve without certification. The plant’s LDAR programme subsequently identifies the valve as a leaking source. Remediation requires either replacing the packing (expensive, requires a shutdown and may not achieve certification) or replacing the valve with a certified unit. The additional cost of specifying ISO 15848-1 Class B on the original order is a small fraction of the remediation cost.
Over-Specification — The Less-Discussed Problem
While under-specification is the more common error, over-specification imposes real costs that are often not recognised. Over-specification on a valve data sheet means specifying requirements that are more stringent than the application requires, adding cost without adding engineering value.
Common over-specification examples: Specifying Class VI (zero leakage) seat shutoff on a process isolation valve where the service fluid is non-toxic, the process can tolerate minor internal leakage across the closed valve, and Class III or IV would be perfectly adequate. The Class VI seat requires a soft seat or precision metal-to-metal seat with higher manufacturing cost, more demanding testing, and a seat that may have shorter service life in abrasive or dirty service than a Class III hard-metal seat.
Specifying 100% radiographic testing (RT) of all welds on a carbon steel gate valve in utility steam service at Class 150, where the industry standard (ASME B16.34 Examination Class 1) requires only visual examination. The RT adds significant cost (typically 10-20% of valve cost for a small valve) and lead time without improving the safety case for a Class 150 utility steam valve.
Specifying SIL 2 certification for an ESD valve in a function where the risk assessment shows SIL 1 is adequate. SIL 2 certification requires more extensive valve and actuator qualification documentation, more frequent proof testing, and potentially a more complex valve design — all at additional cost. If SIL 1 is adequate for the quantified risk, SIL 2 specification adds cost without reducing risk.
The Data Sheet Review — Engineering Quality Assurance
A structured data sheet review process — either internal peer review or using a standardised checklist — is the most effective tool for eliminating both under-specification and over-specification errors. A good checklist covers:
Service data completeness: Are all operating conditions defined (normal, minimum, maximum, shutdown, design)? Is shut-off differential pressure defined? Is the fluid composition fully characterised (including trace components that affect corrosion and material selection)?
Material specification: Is the NACE sour service requirement addressed? Is the low-temperature charpy requirement stated for cryogenic or low-temperature service? Is the oxygen service cleaning requirement stated for any oxygen service? Are elastomeric seal materials specified by material designation, not just by generic name?
Seat leakage: Is the required seat leakage class specified by API 598 class number? Is it appropriate for the service (not over-specified, not under-specified)?
Actuator: Is the fail-safe action unambiguously stated? Is the minimum available supply pressure stated for actuator sizing? Is the required response time stated for ESD applications? Is the SIL requirement stated if applicable?
Testing and inspection: Is the NDE level appropriate to the service criticality? Is the fugitive emission testing specified if required? Is the fire-safe certification specified for any valve in hydrocarbon service? Is the FAT requirement defined?
Valve data sheet engineering is perhaps the least glamorous aspect of valve engineering. It involves careful attention to detail rather than creative engineering problem-solving. But it is the point at which engineering intent is converted into a binding technical specification — and every error in that specification propagates into a non-conforming valve that either must be replaced (at full cost plus delay) or enters service with a known technical deficiency. The engineer who writes complete, correct valve data sheets every time is delivering consistent engineering quality that the rest of the project depends on.