API · ASME · DIN · EN standard industrial valves
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 liquid-filled systems and duty where a full-bore pop would overshoot the upset. The range covers a spring-loaded execution with bodies in cast iron, WCB, SS304 or SS316 and a nozzle, adjusting ring, disc, guide sleeve and stem set 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. The lift classes frame the choice: low lift opens only 1/24th of the bore (micro-lift executions 1/40-1/20 of the throat) so discharge area follows disc position and capacity stays modest, against high lift at 1/12th and full lift where the curtain area stops mattering altogether. ASME code windows bound the action - boiler valves open within 3% and close within 4%, Section VIII valves within 10% and 7% - and on compressible fluids chatter starts when the inlet piping drop (code limit 3% of set pressure, GB 12241 the lesser of 3% and 1/3 of blowdown) exceeds the 7-10% blowdown, a quantitative-stability question the industry still leaves unsettled. The easing lever should be exercised above 75% of set pressure in routine checks to prevent seizing. Selection turns on the liquid versus compressible duty, set pressure inside the PN/Class band, and trim materials against the medium.
Part of the Safety Valves family
Last updated: 2026-11
Family specifications
| set pressure range | 0.1 to 1.6 MPa |
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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 | -20 to 425°C (ductile iron ≤300°C, WCB ≤425°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 |
| low lift definition limited opening | Low lift: the disc lifts only 1/24th of the bore diameter, the discharge area is determined entirely by disc position, and capacities are much lower than full- or high-lift valves of the same size |
| high lift definition between low and full | High lift (the intermediate execution) lifts at least 1/12th of the bore diameter, where the curtain area - and ultimately disc position - still determines the discharge area |
| full lift definition curtain area | Full lift: the disc lifts sufficiently that the curtain area no longer influences the discharge area - the defining contrast with low-lift valves |
| asme code opening blowdown windows | ASME code windows: ASME I boiler valves open within 3% overpressure and close within 4%; ASME VIII pressure-vessel valves open within 10% overpressure and close within 7% |
| proportional action liquid systems | Proportional-type action is characteristic of relief valves used in liquid systems; this proportionate behaviour is what low-lift executions trade against the full-bore pop |
| easing lever periodic manual lift | Standard safety valves are generally fitted with an easing lever for manual lifting to confirm operation at pressures above 75% of set pressure, done as part of routine safety checks or maintenance to prevent seizing |
| micro lift opening height gb definition | Chinese micro-lift (微启式) definition: opening height below 1/4 of the flow diameter, typically 1/40-1/20, with proportional action |
| micro lift used for liquid media | Micro-lift valves are mainly used for liquid service, and only occasionally for very small gas discharge |
| micro lift throat area definition mihana | Japanese manufacturer definition: micro-lift valves open a small height, usually 1/40-1/20 of the seat (throat) diameter, with the seat flow area only slightly larger than the throat area |
| inlet pressure drop 3pct rule | Code rule: inlet piping pressure drop between the protected equipment and the safety valve must not exceed 3% of set pressure (API 520; GB 12241 takes the lesser of 3% of set pressure and 1/3 of the maximum blowdown) |
| chatter mechanism inlet drop vs blowdown | Chatter mechanism on compressible fluids: blowdown is typically 7-10% of set pressure, and when the inlet pressure drop exceeds the blowdown the valve chatters or flutters |
| inlet pressure drop stability engineering | Stability during relief is a key valve characteristic: inlet piping pressure drop is a recognized major factor behind disc chatter or flutter, but how to evaluate its influence quantitatively remains unsettled |
| 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
| gas service positioning | Gas-service positioning: the page presents low-lift as liquid-dominant (proportional action, mainly liquid service, gas only at very small discharge), while the spec list carries the same API 520/526/527 design standards as the full-lift page; gas applications should be scoped to small discharge or referred to full-lift. |
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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 low 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 low 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 low 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 low lift safety valves cover?
The published working temperature range is -20 to 425°C (ductile iron ≤300°C, WCB ≤425°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 low 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 low 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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