API · ASME · DIN · EN standard industrial valves
Safety Valves
Automatic pressure-relief devices protecting boilers, vessels and piping against overpressure, sized to API 520/521/526.
Last updated: 2026-11
Find your valve by specs Enter size, pressure class, set pressure and temperature — the selector narrows the published pages that evidence them. Open the selector →Family specifications
| pressure class | PN16 to PN100, Class 150 to Class 600 |
|---|---|
| size range | 1/2 x 1/2 inch to 12 x 14 inches, depending on model |
| body materials | Cast iron, Ductile iron, WCB, SS304, SS316 |
| end connections | Threaded NPT, Flanged RF or RTJ facing |
| design standards | API 520, API 521, API 526 |
| testing standards | API 527, ASME PTC 25.3, API 598, DIN 3230 |
| blowdown range | Blowdown typically varies from roughly 2-20%; some valves offer adjustable blowdown |
| nozzle and disc materials | SS304, SS316, 2Cr13 |
| service media | Steam, Gas, Vapour, Water, Compatible liquids |
| working principle | Opens automatically at a predetermined set pressure to protect pressure vessels and other equipment from pressures exceeding their design limits |
| reseat blowdown | Blowdown is stated as a percentage of set pressure - how much the pressure must drop before the valve reseats |
| loading options | Spring-operated as standard; diaphragms at lower pressures; oldest designs used a weight |
| relief valve liquid duty | Relief valve (liquid service) opens proportionally as rising pressure overcomes the spring |
| safety valve gas duty | Safety valve (gas service) is full-lift or snap acting - pops completely open |
| pop action speed | Pop action snaps into full lift in milliseconds; a disc skirt exposes larger area to create more lifting force |
| protection types | Thermal protection uses small-orifice valves for liquid thermal expansion; flow protection uses considerably larger valves sized for rapid discharge of gas or high liquid volumes |
| thermal relief rationale | Small thermal-relief valves suffice because liquids are nearly incompressible - a small discharge produces a substantial pressure reduction |
| manual lever note | Pressure safety valves carry a manual lever for emergency actuation |
| compressible fluid scope | Compressible-fluid safety valve usually opens completely, accompanied by a popping sound |
| api526 standardization | API 526 executions use standardized capacities, installation dimensions and materials, with design and selection standardized per API 520 |
| set pressure envelope ref | Industrial reference envelope: set pressure 0.2-400 barg (2-5,802 psig) |
| temperature envelope ref | Industrial reference temperature envelope: -273 to 550 °C (-450 to 1,000 °F) |
| orifice letters ref | Industrial reference orifice span: API 526 letters D through T |
| connection envelope ref | Industrial reference connection span: DN 25 to DN 200 / NPS 1 to NPS 8 |
| trim robustness | Service life extended by hardened discs, stellited seats and shielded bellows |
Scope & source notes
| set pressure envelope | Set-pressure envelope: the referenced industrial executions span up to 400 barg (5,802 psig), far above the tenant PN16-PN40 / Class 150-300 band - the tenant range covers only the low-pressure segment of the referenced envelope. |
|---|---|
| temperature envelope | Temperature envelope: the referenced -273 to 550 °C execution span has no tenant counterpart - the tenant page states no temperature limits for its materials. |
| duty type split | Duty-type split: proportional opening is specific to liquid relief valves while full-lift pop action belongs to compressible-fluid safety valves - the tenant family mixes full lift, low lift and steam lines without mapping each to its opening behavior. |
| testing emphasis | Testing emphasis: the tenant testing standards cover seat tightness (API 527) and performance (ASME PTC 25.3), while the referenced OEM line also cites exceeding API 527 tightness requirements through seat finishing - tenant tightness margin is not quantified. |
Ordering & documentation
Documents
Ask for the documentation set with the inquiry — typical items (material certificates, test reports to the listed inspection standard, dimensional drawings) are confirmed and supplied with the quotation.
Quotation
Send the medium, temperature, pressure, size and connection for a quotation-ready inquiry. Lead time, MOQ and price are confirmed at quotation, together with the documents to be supplied with the order.
Sample & supply
Supply terms, order quantities and lead time are agreed per order — state the destination country and required schedule with the inquiry.
Storage & shipping
Store valves with seats and seals protected from UV, ozone and deformation, and keep end-face protectors on until installation; storage limits and shipping arrangements for the selected materials are confirmed at quotation.
Frequently asked questions
What standards govern the design and testing of safety valves?
The published specification for this family lists API 520, API 521, API 526 as the design standards. Testing follows API 527, ASME PTC 25.3, API 598, DIN 3230.
What sizes and pressure ratings are available for safety valves?
The published size range is 1/2 x 1/2 inch to 12 x 14 inches, depending on model, and the published pressure ratings are PN16 to PN100, Class 150 to Class 600. Availability of a specific size and rating is confirmed at quotation.
What materials are safety valves available in?
The published specification lists body materials: Cast iron, Ductile iron, WCB, SS304, SS316. Material availability for a specific size and rating is confirmed at quotation.
What end connections do safety valves support?
The published specification lists Threaded NPT, Flanged RF or RTJ facing as the available end connections. The connection for a specific size is confirmed at quotation.
What should a quotation inquiry for safety valves include?
The governing standard and class, nominal size, body and seat materials, the service medium with temperature, and the destination — anything missing is confirmed during quotation.
Knowledge: selection guides
Types in this family
Type
Full Lift Safety Valves
Full lift safety valves pop wide open once set pressure is reached, dumping the full orifice area so accumulated pressure collapses fast on compressible or two-
View specifications →Type
Low Lift Safety Valves
Low lift safety valves open only a fraction of the seat diameter, releasing a measured slip of fluid along a seat face — the proportionate behaviour that suits
View specifications →Type
Steam Safety Valves
Steam safety valves guard boilers and steam headers, venting overpressure flashes before they can lift a vessel rating — sized on the inlet-by-outlet paired fla
View specifications →Type
Balanced Bellows Safety Valves
Balanced bellows safety valves hold set pressure stable where back pressure would derate a conventional spring-loaded relief valve: a bellows isolates the sprin
View specifications →Type
Pilot-Operated Safety Valves
Pilot-operated safety valves pair a main valve with an external pilot: the pilot senses line pressure and controls the main valve, giving full lift at set press
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Preparing a larger or non-standard requirement? The Safety Valves quotation guide explains what to include, the standard ranges and custom options, and the documents to attach.
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