API · ASME · DIN · EN standard industrial valves
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-phase service around boilers, receivers and vessels. The range covers a spring-loaded execution with bodies in cast iron, WCB, SS304 or SS316 and a trim set — nozzle, adjusting ring, disc, guide sleeve and stem — in 2Cr13, SS304 or SS316, under a carbon-steel bonnet and cap with a steel spring and 2Cr13 adjusting bolt. Working pressure spans PN1.6 to PN4.0 and Class 150 to Class 300 with NPT, RF or RTJ ending. Design follows the API 520/521/526/527 relief series with ASME 25.3, face-to-face per ASME B16.10, EN 558-1 or DIN 3202, flanges per ASME B16.5, DIN 2543/2545 or EN 12627, and API 598 / DIN 323 testing. Operation sits on narrow margins: roughly 10% overpressure (3%-21% by code) buys full lift, blowdown of -4% to -20% sets the reseat point, and operating pressure must stay below that reseat point to avoid simmer - the audible leak between seat and disc that starts near 90-95% of set pressure. Chatter, the rapid plug-on-seat oscillation that can reach hundreds of hertz, follows excessive inlet loss (the cumulative non-recoverable inlet loss must stay within 3% of set pressure at nameplate capacity) or oversizing, and shows up as seat damage, spring fatigue and stem galling; API 527 caps metal-seat leakage at 90% of set pressure and API 526 letter orifices D-T frame the area selection. Selection turns on set pressure against the working-pressure band, seat and nozzle materials versus medium, and the threaded or flanged end the line carries.
Part of the Safety Valves family
Last updated: 2026-11
Family specifications
| set pressure range | 0.1-10 MPa (0.1-2 at class 150; 1.6-5 at class 300; 3.2-10 at class 600) |
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| pressure class | PN1.6, PN2.5, PN4.0, Class 150 to Class 300 |
| size range | DN32–DN150 |
| body materials | Cast Iron, WCB, SS304, SS316 |
| body materials | Carbon Steel |
| nozzle materials | 2Cr13, SS304, SS316 |
| disc materials | 2Cr13, SS304, SS316 |
| end connections | NPT, RF, RTJ |
| temperature range | ≤300°C |
| design standards | ASME 25.3, API 520, API 521, API 526, API 527 |
| testing standards | API 598, DIN 323 |
| face to face | ASME B16.10, EN558-1, DIN 3202 |
| adjusting ring materials | 2Cr13, SS304, SS316 |
| guide sleeve materials | 2Cr13, SS304, SS316 |
| spring materials | Steel |
| stem materials | 2Cr13, SS304, SS316 |
| adjusting bolt materials | 2Cr13 |
| cap materials | Carbon Steel |
| flange standards | ASME B16.5, DIN 2543, DIN 2545, EN 12627 |
| overpressure allowance 10pct full lift | ASME/API practice allows roughly 10% overpressure for valves on unfired systems so the pop-action valve can achieve full lift and rated capacity; the huddling chamber assists the lift effort |
| overpressure typical range leser | Overpressure is usually expressed as a percentage of set pressure; a typical value is 10%, ranging between 3% and 21% depending on the code and application |
| blowdown definition crosby | Blowdown is the difference between the set pressure and the closing-point (reseat) pressure, expressed as a percentage of set pressure; where the closing point sits is determined by the control-chamber design |
| blowdown typical values leser | Typical blowdown values defined in codes and standards are -7% and -10%, ranging from -4% to -20% depending on the code and service (steam, gas or liquid) |
| operating margin vs blowdown crosby m11 | Operating pressure must stay below the reseating pressure: set at 100 psig with 7% blowdown the valve closes at 93 psig, so operation must remain below 93 psig to prevent leakage or flow from a partially open valve |
| inlet loss 3pct rule crosby | Inlet piping rule: the cumulative total of all non-recoverable inlet losses shall not exceed 3% of the valve set pressure, evaluated at nameplate capacity corrected for the flowing fluid; upstream system flow characteristics govern |
| chatter definition and causes valfonta | Chatter is the rapid oscillation of the plug on the valve seat - not ordinary vibration - with the moving component repeatedly striking the metal seat at frequencies that can reach hundreds of hertz; main drivers are excessive inlet-pipe pressure loss, oversizing and too-narrow blowdown margin, with seat/plug deformation, spring fatigue and stem galling as the damage modes |
| chatter cause summary projectmaterials | Chatter is rapid opening and closing of the valve disc, caused by excessive inlet pressure drop (over 3% of set pressure) or an oversized valve; simmer on spring-loaded valves begins at approximately 90-95% of set pressure |
| simmer definition crosby | Simmer is the audible or visible escape of fluid between the seat and disc at an inlet static pressure below the popping pressure and at no measurable capacity; it applies to safety or safety relief valves on compressible-fluid service |
| api527 seat leakage and api526 orifice | API 527 seat-tightness testing applies 90% of set pressure and limits metal-seated gas valves to 40 SCFH air up to 1,000 psig, and 0.60 SCFH air per inch of orifice diameter above 1,000 psig, while soft-seated valves must show zero leakage; API 526 standardizes orifice sizes by letter designation D through T, selected as the next larger standard orifice after the API 520 Part I required area |
| adjusting ring | 2Cr13, SS304, SS316 |
| guide sleeve | 2Cr13, SS304, SS316 |
| adjusting bolt | 2Cr13 |
| end connection | NPT, RF, RTJ |
| end connection dimension | ASME B16.5, DIN 2543, DIN 2545, EN 12627 |
Scope & source notes
| overpressure wording | Overpressure wording: Crosby handbook gives the general 10% allowance for valves on unfired systems, while LESER states the code range spans 3%-21% by code and application; the page should quote 10% as typical, not as a universal limit. |
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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 full lift safety valves?
The published specification for this family lists ASME 25.3, API 520, API 521, API 526, API 527 as the design standards. Testing follows API 598, DIN 323.
What sizes and pressure ratings are available for full lift safety valves?
The published size range is DN32–DN150, and the published pressure ratings are PN1.6, PN2.5, PN4.0, Class 150 to Class 300. Availability of a specific size and rating is confirmed at quotation.
What materials are full lift safety valves available in?
The published specification lists body materials: Cast Iron, WCB, SS304, SS316. Material availability for a specific size and rating is confirmed at quotation.
What working temperature range do full lift safety valves cover?
The published working temperature range is ≤300°C. For a medium at the edge of the range, confirm the suitability of the selected seat and body materials at quotation.
What end connections do full lift safety valves support?
The published specification lists NPT, RF, RTJ as the available end connections. The connection for a specific size is confirmed at quotation.
What should a quotation inquiry for full lift 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.
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