Safety Valve Selection & Sizing Connection Size Does Not Prove Safety Valve Capacity Certified relieving capacity is the engineering evidence that a safety valve can discharge the required load under defined relieving conditions. Connection size only confirms how the valve connects to the piping system. For spring loaded safety valves, confusing these two values can …
Safety Valve Selection & Sizing
Connection Size Does Not Prove Safety Valve Capacity
Certified relieving capacity is the engineering evidence that a safety valve can discharge the required load under defined relieving conditions. Connection size only confirms how the valve connects to the piping system. For spring loaded safety valves, confusing these two values can lead to an installed valve that fits the flange but cannot protect the equipment.
Final selection still depends on the real medium, relief scenario, set pressure, relieving temperature, back pressure, manufacturer data, applicable standard version and project specification.
Quick Answer: Connection Size Is a Fit-Up Detail, Not a Capacity Proof
Connection size tells you how a safety valve connects to the piping system. Certified relieving capacity tells you whether the selected valve can actually discharge the required mass or volume of fluid under defined relieving conditions. Two valves with the same inlet and outlet size may have different internal nozzle areas, lift characteristics, trim designs, certified or documented capacities, pressure ratings, temperature limits and standard bases.
From a pressure-protection perspective, the question is not “Will this 2 × 3 valve fit the flange?” The correct question is “Can this selected valve, at the required set pressure, allowable overpressure, relieving temperature, medium phase, back pressure and applicable code basis, relieve the governing load for the protected equipment?”
Before quotation, confirm the protected equipment, governing relief scenario, medium and phase, operating pressure, MAWP or design pressure, set pressure, required relieving capacity, relieving temperature, inlet and outlet connection, back pressure, material requirements and applicable code basis. For a broader sizing overview, see ZOBAI’s guide to dimensionamento valvole di sicurezza e capacità certificata. For product selection, start with Valvole di sicurezza a molla or the safety valve engineering hub.
What Certified Relieving Capacity Means
Certified relieving capacity is the capacity value associated with a pressure relief device under defined test, calculation, code or manufacturer data conditions. Depending on the project jurisdiction and product certification basis, the value may be shown on the nameplate, catalog, certified capacity table, datasheet or engineering documentation. It is not a visual property of the valve body. It is not guaranteed by nominal connection size alone.
In practical RFQ work, capacity must be tied to the medium and phase, set pressure, relieving pressure, relieving temperature, internal orifice or nozzle design, lift behavior, allowable overpressure and back pressure condition. A large visible connection does not automatically mean a large certified or documented relieving capacity.
Carico di sfioro richiesto
The flow rate that must be discharged for the governing relief scenario, such as fire, blocked outlet, thermal expansion or regulator failure.
Selected valve capacity
The valve capacity checked against the required load under defined medium, pressure, temperature and back-pressure conditions.
Dimensione connessione
The inlet and outlet interface needed for mechanical fit-up, flange/thread standard and piping review, but not proof of capacity.
Selection risk: A valve can have the correct set pressure and the correct inlet/outlet connection, while still being unsuitable if its certified or documented relieving capacity does not cover the required relieving load for the governing relief case.
Pressure Terms Buyers Must Separate Before RFQ
Many connection-size mistakes happen because pressure terms and capacity terms are mixed together. A buyer may send only “DN50, 10 bar,” but that does not define the protected equipment, relieving load, allowable overpressure, accumulation, blowdown or certified capacity basis. Keep the following terms separate before requesting price or replacement.
| Termine | What It Means in Selection | Why It Is Not the Same as Capacity | RFQ Note |
|---|---|---|---|
| Pressione operativa | Normal pressure range of the protected system during operation | It does not define the emergency relieving load | Provide normal, maximum and expected operating margin where available |
| Pressione massima di progetto / Pressione di progetto | Pressure limit basis for the protected equipment or system design | It does not prove the selected valve’s discharge capacity | Confirm whether the project uses MAWP, design pressure or another basis |
| Pressione di taratura | Pressure at which the valve is adjusted to begin opening under specified conditions | A correct set pressure can still be paired with an undersized valve | Do not use set pressure as a shortcut for sizing |
| Sovrapressione | Pressure increase above set pressure during relieving | It affects available relieving pressure but is not a capacity value by itself | Confirm project or code basis for allowable overpressure |
| Accumulo | Pressure increase above MAWP or design pressure during an overpressure event, depending on the applicable basis | It must be reviewed with the governing relief scenario and selected valve | Confirm the applicable definition used by the project |
| Blowdown / reseating pressure | Pressure behavior after opening, including where the valve reseats | It affects operating stability but does not replace required capacity review | Important for steam, boiler and process stability discussions |
| Capacità di sfioro richiesta | Flow that must be discharged for the governing relief case | This is the demand side, not the selected valve’s proof | Provide units, medium, scenario and calculation basis |
| Certified or documented relieving capacity | Valve capacity value documented under defined conditions | It must still match the actual medium, pressure, temperature and back pressure basis | Check against required relieving capacity before approval |
| Perdita di pressione in ingresso | Pressure drop between protected equipment and valve inlet during relieving | It can affect stability and performance, but is not visible from connection size alone | Review inlet line size, length, reducers and fittings |
| Contropressione allo scarico | Pressure at the valve outlet from discharge piping or common headers | It can affect capacity and valve behavior, especially in conventional designs | Confirm superimposed and built-up back pressure separately |
Capacity Validation Matrix: What Must Be Proven Before Selection
Capacity validation is not a single number taken from valve size. It is a match between the protected equipment requirement and the selected valve data. The following matrix separates the engineering inputs that are often mixed together during procurement.
| Engineering Item | Source of Data | Cosa conferma | Cosa può andare storto se mancano |
|---|---|---|---|
| Attrezzatura protetta e scenario di sfioro | Process safety review, vessel/boiler/skid design, project specification | Which overpressure case governs the required relieving load | The valve may be selected for the wrong scenario or an outdated operating case |
| Capacità di sfioro richiesta | Relief calculation or responsible engineer’s datasheet | The flow that must be discharged at relieving condition | The valve may fit the pipe but be undersized for the actual relief load |
| Set pressure and relieving pressure | Equipment MAWP/design pressure, code basis and project rule | Opening setting and pressure available for discharge | Set pressure may be confused with capacity, or pressure definitions may be mixed |
| Mezzo, fase e temperatura di sfioro | Process data, P&ID, operating envelope, relief case | Fluid behavior, density, viscosity, phase and material exposure | Steam, gas, vapor, liquid or two-phase service may be sized or specified incorrectly |
| Certified or documented valve capacity | Manufacturer data, certified capacity table, datasheet, nameplate or approved calculation basis | Whether the selected valve can cover the required relieving load under defined conditions | Nominal size may be mistaken for verified relieving performance |
| Back pressure and outlet system | Discharge piping design, common header data, flare or vent system review | Whether conventional, bellows balanced or another design should be reviewed | Capacity, stability, chatter risk and discharge safety may be affected |
| Perdita di pressione in ingresso | Inlet line size, length, fittings, reducers and installation layout | Whether the valve can open and relieve stably in the installed condition | Chatter, simmer, instability or lower effective performance may occur |
| Material and trim suitability | Medium, temperature, corrosion, cleanliness, seat/seal and project material requirements | Whether body, trim, spring, seat, gasket and bellows materials are appropriate | A mechanically correct valve may fail through corrosion, sticking, leakage or material rating mismatch |
This table does not replace formal sizing. It is a practical RFQ review framework to prevent the most common error: treating the connection size as if it were the capacity basis.
Connection Size vs Certified Relieving Capacity
The engineering difference is simple: connection size supports installation; certified relieving capacity supports protection. Both are necessary, but they answer different questions.
| Elemento di selezione | Cosa ti dice | Cosa non prova | Why It Matters in RFQ |
|---|---|---|---|
| Inlet connection size | Pipe or flange size at the valve inlet | Required relieving capacity, orifice area or certified capacity | Needed for mechanical fit-up and inlet pressure-loss review |
| Outlet connection size | Discharge piping interface | Back-pressure suitability or discharge system adequacy | Needed for outlet piping, drainage, support and safe discharge review |
| Flange class / PN rating | Pressure-temperature rating boundary for the connection | Certified flow capacity or complete valve suitability | Must be checked against design pressure, temperature and material group |
| Orifice / nozzle / flow path | Internal effective flow boundary | Complete suitability without service data | Usually more relevant to capacity than flange size alone |
| Certified or documented relieving capacity | Flow capability under defined conditions | Universal suitability for all media, temperatures or standards | Central evidence for whether the selected valve can protect the equipment |
| Capacità di sfioro richiesta | Load that must be discharged for the governing scenario | Selected valve adequacy until matched with valve data | Core input from process safety, vessel, boiler, skid or equipment design |
Use this comparison as a simplified engineering illustration. It should not be treated as a certified manufacturing drawing or a capacity certificate.
Required Capacity vs Selected Valve vs Certified Capacity
Procurement teams often ask for a valve by size, while engineers approve the valve by capacity. The following table shows how the capacity language should be separated during review.
| Termine | Significato | Who Usually Provides It | Selection Consequence |
|---|---|---|---|
| Capacità di sfioro richiesta | The load that must be relieved for the governing overpressure case | Process safety engineer, equipment designer, EPC, end user or calculation owner | The valve must meet or exceed this need under the correct basis |
| Required area / selected orifice | The calculated or selected flow area/orifice used to meet the required load | Responsible engineer, standard-based sizing workflow or manufacturer review | May drive the internal valve selection more than the external connection size |
| Certified or documented relieving capacity | The manufacturer-certified, documented or project-accepted capacity value under defined conditions | Manufacturer data, certification table, nameplate, datasheet or approved documentation | Used to confirm whether the selected valve protects the equipment |
| Dimensione connessione | The inlet and outlet piping interface | Piping/mechanical design, existing installation or project specification | Used for fit-up and installation checks, not as capacity proof |
Why Same Connection Size Can Have Different Capacity
The same inlet/outlet size can appear across different safety valve designs. This is common in spring loaded safety valves, flanged safety valves and replacement valves where old nameplate data may only show size and set pressure. The capacity difference comes from the internal design, not only the visible connection.
Several factors can change the actual relieving capacity, including nozzle throat area, seat geometry, valve lift, disc holder, guide design, spring chamber arrangement, conventional or bellows balanced configuration, medium phase, set pressure, overpressure allowance, relieving temperature and back pressure.
Final internal geometry and certified or documented capacity must be confirmed against the selected model and project requirements.
For example, two flanged valves may both be described as DN50 × DN80 or 2 in × 3 in, but one may be a lower-capacity design for a specific service and another may use a larger effective orifice. If the buyer only sends “2 × 3 safety valve, 10 bar” without medium, required capacity and standard basis, the quotation may match the pipe connection but fail the relief case.
Why Certified Capacity Matters More for Spring Loaded Safety Valves
A spring loaded safety valve opens when inlet pressure force overcomes spring force. The spring setting determines the opening pressure, but it does not determine the discharge load by itself. Once the valve starts to open, relieving performance depends on lift, nozzle area, disc geometry, flow coefficient, blowdown behavior, pressure drop and discharge condition.
For spring loaded designs, the main selection risk is assuming that set pressure and connection size define the valve. They do not. A correct specification should confirm operating pressure, MAWP or design pressure, set pressure, required relieving capacity, medium and phase, relieving temperature, back pressure, inlet pressure loss, outlet piping, material requirements and applicable standards.
What set pressure does
Set pressure defines the pressure at which the valve is adjusted to begin opening under specified conditions. It does not state the required relieving load or prove capacity.
What certified capacity does
Certified or documented capacity supports the question of whether the selected valve can discharge the required load under defined relieving conditions.
For broader product configuration guidance, see ZOBAI’s page for Valvole di sicurezza a molla and the article on how to select spring loaded safety valves.
The Correct Sequence: Relief Scenario First, Connection Second
The safest selection sequence starts with the protected equipment, not with the valve size. For a boiler, vessel, heat exchanger, compressor, pipeline, tank or skid, the governing relief case may be blocked outlet, fire exposure, regulator failure, thermal expansion, tube rupture, utility failure or another defined scenario. Each case produces a required relieving load.
- Identify the protected equipment and governing relief scenario.
- Confirm MAWP or design pressure, operating pressure and set pressure basis.
- Determine the required relieving capacity for the governing case.
- Define medium, phase, fluid properties and relieving temperature.
- Check allowable overpressure or accumulation under the applicable project rule.
- Select the valve type and internal flow capacity, not only nominal connection.
- Review back pressure, inlet loss, outlet piping and discharge system.
- Confirm material, seat, spring, gasket, bellows or trim requirements.
- Confirm flange/thread standard, pressure-temperature rating and facing.
- Prepare datasheet, nameplate copy, inspection requirements and documentation needs.
Only after the capacity and service conditions are known should connection size be finalized or confirmed. In many projects, the connection is constrained by existing piping, but the piping may still need modification if the required safety valve capacity, inlet pressure loss or outlet discharge design cannot be achieved safely.
Typical Mistakes When Buyers Select by Connection Size
Mistake 1: Treating DN or NPS Size as Flow Capacity
DN and NPS are nominal connection systems. They are not a certified capacity statement. A DN50 valve may not have the same capacity as another DN50 valve from a different series, design, standard basis or internal orifice.
Mistake 2: Ignoring Medium and Phase
Steam, air, gas, liquid and two-phase service are not interchangeable for sizing. A valve capacity stated for steam cannot simply be treated as liquid capacity. Fluid properties and phase behavior must be confirmed.
Mistake 3: Using Set Pressure as a Shortcut for Sizing
Set pressure is the pressure at which the valve is adjusted to begin opening under specified conditions. It is not the required relieving load. A valve can have the correct set pressure but still be undersized for the fire case, blocked outlet case or other governing scenario.
Mistake 4: Overlooking Back Pressure
Back pressure can reduce capacity, affect opening and closing behavior and create instability. Conventional spring loaded valves may be sensitive to variable built-up back pressure. Balanced bellows or other configurations may be required, but this must be checked against actual service conditions. For detailed review, see ZOBAI’s Contropressione e soffietto guida.
Mistake 5: Replacing by Old Valve Appearance
Replacement by appearance is risky. The old valve may have been oversized, undersized, incorrectly installed or selected under a previous operating condition. At minimum, provide the old nameplate, photos, datasheet, medium, set pressure, connection standard and required capacity basis.
Mistake 6: Assuming a Standard Name Completes the Specification
API, ASME, ISO, EN, DIN, GB or project specifications may guide sizing, construction, testing, marking or dimensions, but a standard name alone does not complete a valve selection. For API-related sizing context, see ZOBAI’s API 520 dimensionamento valvole di sicurezza guide. For flanged steel PRV dimensional context, see API 526 valvole di sicurezza flangiate.
Mistake 7: Treating a Quotation as Final Engineering Approval
A commercial quotation may list a valve size, material, connection and set pressure. It should not be treated as final approval unless the required capacity, capacity basis, medium, relieving temperature, back pressure, installation condition and applicable document requirements have been reviewed.
Replacement Verification Workflow: Do Not Replace by Size Alone
Replacement inquiries are where connection-size mistakes happen most often. A buyer may provide only photos, connection size and set pressure from an old valve. That information helps identify the installation envelope, but it does not prove that the old valve was correctly sized or that the new valve will be acceptable.
| Replacement Step | Dati da verificare | Motivo tecnico | Proceed / Hold |
|---|---|---|---|
| 1. Identify old valve | Nameplate, model, serial number, photos, inlet/outlet size, connection standard | Confirms what is installed, but not whether it is correct | Proceed only as identification |
| 2. Confirm protected equipment | Equipment tag, MAWP/design pressure, service duty, original datasheet if available | Confirms what the valve is protecting | Hold if equipment duty is unknown |
| 3. Confirm relief scenario | Blocked outlet, fire, thermal expansion, regulator failure, tube rupture or other basis | Determines the required relieving load | Hold if scenario is unknown |
| 4. Confirm required capacity | Relief calculation, datasheet capacity value, capacity units and basis | Confirms whether the replacement can protect the equipment | Hold if capacity basis is missing |
| 5. Check installation condition | Inlet line, reducers, outlet header, back pressure, support, drainage | Prevents chatter, outlet load and back-pressure problems | Proceed with installation review |
| 6. Confirm documentation | Test certificate, material certificate, capacity basis, inspection scope, project standard | Supports QA, inspection and end-user approval | Proceed only when required documents are defined |
Procurement rule: A “same size replacement” should be treated as a starting point, not a final specification. If the old valve capacity, relief case or installation condition cannot be confirmed, request engineering review before purchase.
Testing, Documentation and Capacity Basis
Testing and documentation are not the same as final sizing, but they are important parts of engineering review. Set pressure calibration, seat tightness testing, material records, datasheets and capacity basis information help engineers and inspectors understand whether the selected valve can be accepted for the project.
This visual should not be interpreted as a claim of certification for any specific model. Certification and documentation requirements must be confirmed by project and selected valve.
| Documento / Verifica | Cosa supporta | What It Does Not Replace |
|---|---|---|
| Set pressure test record | Confirms calibration or adjustment condition | Required relieving capacity calculation |
| Test di tenuta sede | Supports leakage acceptance under defined test conditions | Material compatibility or capacity suitability |
| Certificato materiale | Supports body, trim or pressure-containing material traceability where required | Service suitability without medium and temperature review |
| Capacity basis / certified capacity data | Supports comparison with the required relieving load | Universal suitability for all media or installation conditions |
| General arrangement or dimensional drawing | Supports fit-up, envelope and connection review | Capacity proof unless tied to selected valve data |
How Back Pressure and Installation Can Change the Decision
Even if a valve has sufficient rated or certified capacity under standard conditions, the installed system can create performance problems. Inlet pressure loss can cause simmer, chatter or unstable operation. Outlet piping can create built-up back pressure that reduces flow or affects valve behavior. Heavy discharge piping can impose mechanical loads on the valve body. Poor drainage can allow condensate or liquid accumulation.
This is why capacity review and installation review must be connected. A correct datasheet should support safe installation through inlet/outlet connection details, pressure-loss assumptions, discharge routing, back-pressure condition, reaction force consideration, drainage and support. For detailed installation checks, see the guida all'installazione delle valvole di sicurezza.
| Installed Condition | Engineering Effect | Dati da confermare |
|---|---|---|
| High inlet pressure loss | May cause chatter, instability or reduced effective performance | Inlet line size, length, reducers, elbows and calculated pressure loss |
| Sovrapposizione di contropressione variabile | May affect opening pressure, capacity and stability for conventional designs | Outlet header pressure range and discharge system behavior |
| Contropressione generata durante lo sfioro | May reduce capacity and require configuration review | Outlet piping, header, vent or flare system design |
| Tubazioni di scarico non supportate | May impose load on the valve body and nozzle | Pipe support, reaction force and discharge direction |
| Poor drainage or trapped liquid | May affect discharge safety, corrosion or valve operation | Drainage, orientation and low-point design |
Medium, Material and Service Screening
Certified relieving capacity is only meaningful when the service condition is correctly described. Medium, phase, relieving temperature and compatibility requirements may change the selected valve type, trim, seat, spring, bellows and documents. Material grade alone does not prove suitability.
| Condizione di servizio | Perché è Importante | Selection Data Needed | Do Not Assume |
|---|---|---|---|
| Vapore | Capacity basis, temperature, blowdown and discharge safety are critical | Steam pressure, temperature, required capacity, boiler/vessel data and lever requirement where applicable | Do not use gas or liquid capacity as steam capacity without review |
| Gas or vapor | Compressibility, molecular weight and relieving pressure affect sizing | Gas composition, molecular weight or density, temperature, set pressure and back pressure | Do not select by connection size and set pressure alone |
| Liquido | Viscosity, density and overpressure basis may differ from gas/vapor service | Liquid properties, required flow, temperature and discharge condition | Do not treat liquid and gas service as interchangeable |
| Servizio bifase o in cavitazione | May require special calculation method and engineering review | Relief scenario, fluid data, phase behavior and project sizing basis | Do not apply a simple single-phase shortcut |
| Corrosive or dirty service | Material, seat, spring and trim exposure can affect reliability | Composition, corrosion allowance, solids, polymerizing tendency and cleaning requirements | Do not rely on body material only |
| Cryogenic or high-temperature service | Pressure-temperature rating, seat, spring and gasket selection may change | Relieving temperature, operating temperature range and material requirements | Do not apply a general product temperature range to every model |
When Connection Size Is Still Important
Connection size should not be ignored. It is essential for mechanical fit-up with protected equipment or inlet piping, flange class, face type, thread form, gasket compatibility, pressure-temperature rating review, inlet pressure loss control, outlet discharge piping design and replacement planning where existing piping cannot easily change.
Engineering rule: Use connection size to check fit and piping. Use certified or documented relieving capacity to check whether the valve can protect the equipment. If the two conflict, the solution may require a different valve series, different orifice, piping modification or updated relief calculation.
How Standards Should Be Used in This Decision
Standards help define methods, terminology, dimensions, testing, marking or documentation expectations, but they do not remove the need for real process data. API 520 is commonly used for sizing and selection communication, while API 526 is often used for flanged steel pressure relief valve dimensional and orifice-related RFQ discussions. ASME, ISO, EN/DIN, GB and project specifications may impose additional rules depending on the equipment, jurisdiction and industry.
A standard reference should be translated into a practical valve specification. A useful inquiry does not say only “API safety valve required.” It states the medium, set pressure, required capacity, relieving temperature, back pressure, connection standard, material, documentation scope and project standard basis.
| Standard / Project Requirement Can Help Define | It Does Not Automatically Prove |
|---|---|
| Sizing method, terminology and pressure-relief calculation basis | That a selected valve has enough capacity without actual service data |
| Flanged valve dimensions, orifice families or connection expectations where applicable | That connection size alone equals certified relieving capacity |
| Testing, marking, inspection and documentation expectations | That every valve model automatically carries every certification or document |
| Pressure-temperature rating and material-related review points | That a material grade alone is suitable for the medium, temperature and service condition |
RFQ / Selection Parameters Checklist
The following checklist helps engineers, procurement teams and maintenance personnel prepare a technically reviewable inquiry.
Do not replace missing engineering data with assumptions. Mark unavailable data as “to be confirmed” for review.
| RFQ / Selection Parameter | What to Provide | Perché è Importante |
|---|---|---|
| Apparecchiatura protetta | Boiler, vessel, pipeline, compressor, exchanger, tank, skid or other equipment | Defines the protection duty and applicable design basis |
| Scenario di sfioro | Fire, blocked outlet, regulator failure, tube rupture, thermal expansion or other case | Determines the required relieving load |
| Fluido e fase | Steam, air, gas, vapor, liquid, two-phase, corrosive, cryogenic, viscous or dirty service | Controls sizing method, material choice and valve configuration |
| Pressione operativa / MAWP / pressione di taratura | Normal operating pressure, design pressure or MAWP, and required set pressure | Needed to check pressure definitions, margin and code basis |
| Capacità di sfioro richiesta | Flow rate, units and calculation basis | Central input for matching certified or documented capacity |
| Temperatura di sfioro | Temperature at relieving condition | Affects fluid properties, material rating and seat/seal selection |
| Contropressione | Superimposed and built-up, constant or variable | Determines whether conventional, bellows balanced or other design is suitable |
| Connessione ingresso e uscita | Size, flange/thread standard, rating, facing and material | Required for mechanical fit, pressure-loss review and discharge piping |
| Material requirements | Body, trim, spring, seat, seal, gasket and bellows where applicable | Needed for corrosion, temperature and compatibility review |
| Applicable standard and documents | Project standard, datasheet, capacity basis, test certificate, MTC or inspection scope | Needed for engineering approval, QA and procurement records |
Technical References for Capacity and Overpressure Review
The following references are provided for engineering orientation and RFQ communication. They should not be treated as copied standard text, certification proof for any specific ZOBAI valve model or a substitute for project-specific code review.
| Riferimento | Why It Is Relevant | Use Boundary |
|---|---|---|
| National Board NB-18 Pressure Relief Device Certification | Useful for understanding pressure relief device certification context, manufacturer/device listings and certified relieving capacity references. | Does not prove that a particular valve is suitable for your project without selected model data and operating conditions. |
| ASME BPVC Section XIII: Rules for Overpressure Protection | Provides official context for overpressure protection of pressurized equipment such as boilers, pressure vessels and piping systems. | Does not replace local jurisdiction review, project specification or manufacturer-certified data. |
| API 520 Part II: Sizing, Selection and Installation of Pressure-Relieving Devices | Provides official API context for PRD installation and engineering analysis related to installation review. | Should be used as standards context, not as a standalone valve selection or certification claim. |
FAQ
La dimensione della connessione è la stessa della capacità della valvola di sicurezza?
La dimensione della connessione descrive l'interfaccia di ingresso e uscita. La capacità dipende dall'area di flusso interna, dall'alzata, dalla pressione, dal fluido, dalla temperatura, dalla contropressione e dai dati di prestazione certificati o documentati.
Due valvole di sicurezza con la stessa dimensione di ingresso e uscita possono avere capacità di scarico diverse?
Sì. La stessa dimensione nominale di connessione può essere utilizzata con diversi design interni, orifizi, caratteristiche di alzata e valori di capacità. Verificare sempre la base di capacità certificata o documentata.
La pressione di taratura è sufficiente per selezionare una valvola di sicurezza a molla?
La pressione di taratura definisce la pressione di apertura, ma non il carico di scarico richiesto. È necessario inoltre confermare la MAWP o la pressione di progetto, la sovrapressione ammissibile, il fluido, la capacità richiesta, la temperatura, la contropressione e le condizioni di installazione.
Cosa succede se ho solo una vecchia targhetta identificativa della valvola?
Inviare la foto della targhetta, le foto della valvola, la scheda tecnica esistente se disponibile, i dati dell'attrezzatura protetta e le condizioni operative. Una sostituzione non deve essere approvata solo dall'aspetto o dalle dimensioni di connessione.
La dimensione della connessione API 526 dimostra la capacità della valvola?
L'API 526 è utile per la comunicazione RFQ dimensionale e relativa all'orifizio per valvole di sicurezza flangiate in acciaio, ma la selezione effettiva richiede ancora una base di dimensionamento, il fluido, la pressione, la temperatura, la contropressione e i requisiti di capacità.
Quando dovrei considerare una valvola di sicurezza bilanciata a soffietto?
Un design bilanciato a soffietto può essere considerato quando la contropressione influisce sulle prestazioni delle valvole convenzionali, ma l'idoneità dipende dall'entità e dal tipo di contropressione, dal fluido, dalla temperatura, dai limiti dei materiali e dai dati del produttore.
Quali dati sono più importanti prima di richiedere un preventivo?
I dati più importanti sono mezzo e fase, pressione di taratura, MAWP o pressione di progetto, capacità di scarico richiesta, temperatura di scarico, contropressione, standard di connessione ingresso/uscita, requisiti dei materiali e codice applicabile o requisiti di documentazione.
Posso utilizzare la capacità certificata per un fluido diverso?
La capacità deve essere verificata rispetto al fluido effettivo, alla fase, alle proprietà del fluido, alla pressione di scarico, alla temperatura di scarico e alla base di dimensionamento applicabile. Il servizio con vapore, gas, vapori, liquidi e bifase non deve essere trattato come intercambiabile.
L'ufficio acquisti dovrebbe approvare un preventivo per una valvola di sicurezza se mancano i dati di capacità?
No. Se la capacità di sfioro richiesta o la base di capacità sono mancanti, il preventivo deve rimanere tecnicamente aperto. L'ufficio acquisti può confermare le ipotesi di prezzo e consegna, ma l'approvazione tecnica richiede la revisione della capacità e delle condizioni di servizio.
Ask ZOBAI to Review Capacity Before You Buy by Connection Size
Connection size can help a valve fit the piping, but certified relieving capacity helps confirm whether the valve can protect the equipment. If you are evaluating or replacing a spring loaded safety valve, send ZOBAI your operating conditions, relief calculation or existing nameplate for review.
For a faster engineering review, include:
- Protected equipment and relief scenario;
- Medium and phase, operating pressure, MAWP or design pressure, and set pressure;
- Required relieving capacity with units and calculation basis;
- Relieving temperature, back pressure, inlet/outlet connection and material requirements;
- Existing datasheet, nameplate photo, project standard and required documents where available.
