SUPERLOK® NORTH AMERICA · VALVE ENGINEERING
High Pressure Relief Valves: Rating, Seat and Spring
What the listed pressure range, spring bands and seal options mean once set points run into the thousands of psi.
A high pressure relief valve for instrument tubing is a spring, a seat and a seal in a small body, and each of the three behaves differently when the set point climbs from hundreds of psi to thousands. This note works through that for Superlok® high pressure relief valves, using only what the manufacturer’s pages state. According to the Fundamentals Handbook that the U.S. Department of Energy published for its facilities, a public-sector reference rather than a vendor catalog, most relief and safety valves open against a compression spring, and the valve lifts where system pressure overcomes spring pressure.
The Force Behind a High Pressure Relief Valve
The handbook describes two opposing forces: system pressure tries to push the disk off the seat, and the spring pushes it on. The valve opens when fluid force wins. To see how that scales, use the listed 4.8 mm orifice, which has an area of about 0.028 sq in. If the seat seals across that full diameter, an assumption the pages do not state, the load the spring must resist is about 6 lbf at 225 psig and about 168 lbf at 6000 psig. That is a ratio near 27 to 1 across one product range.
A single spring cannot span that. The manufacturer’s relief valve PDF says multiple springs cover different set pressure ranges, and the catalog lists the springs as separate kits. So a high set point starts with choosing the spring that suits the band.
| Designator and color | Range, psig | Band width, psi | 5% of band top, psi |
|---|---|---|---|
| Y, yellow | 225 to 750 | 525 | 37.5 |
| P, purple | 750 to 1500 | 750 | 75 |
| O, orange | 1500 to 2250 | 750 | 112.5 |
| B, brown | 2250 to 3000 | 750 | 150 |
| W, white | 3000 to 4000 | 1000 | 200 |
| R, red | 4000 to 5000 | 1000 | 250 |
| G, green | 5000 to 6000 | 1000 | 300 |
Ranges are as printed. The last two columns are our arithmetic. Adjacent bands share end values, so a set point at a boundary needs a spring named on the order.
Seat and Seal Choices You Have to Confirm
Seal and seat options vary by variant. The catalog listing names Buna N and FFKM seal options on specific variants, and the relief valve literature shows a PTFE seat with fluoroelastomer O-rings. The body is corrosion-resistant stainless steel, with 316 named on specific variants, and the literature lists 304 stainless steel for the spring, a different grade from the body. Our note on 304 vs 316 covers how the two grades differ. Seal, seat and body grade are confirmed per order against your service fluid and temperature.
What we can say about seals is general. The handbook states that a fine surface finish of the seating area is needed for good sealing, and that the mechanical properties of elastomers fall at higher temperature, with possible destruction of a diaphragm at high pressure. The manufacturer’s category page gives NBR a range of -40 to 121 °C but does not say which seal goes in which valve, and no operating temperature range is stated for the high pressure series. A seal, a fluid and a temperature therefore have to be matched on the order, not assumed from the listing.
What Changes in a High Pressure Relief Valve Above a Few Thousand psi
Three things change. First, tolerance becomes a larger absolute number. The PDF defines set pressure as the upstream pressure at which the first indication of flow occurs, and says it is repeatable within 5 percent after initial relief at room temperature. On the green spring that is up to 300 psi; on the yellow it is under 38. Whether that band is acceptable depends on the weakest component in the protected section, so check the pressure ratings page for tube and fitting limits.
Second, margin shrinks at the top. The catalog lists a cracking range up to 6000 psig and a maximum operating pressure of 6000 psig. A set point at the top of the green band leaves no stated gap to the rating, so allow margin between your set pressure and the 6000 psig maximum. Third, the set definition marks the first indication of flow, not a discharge rate. No source we read gives relieving capacity, reseat pressure or blowdown for these valves, so none is claimed.
The spring sets the range. The catalog describes an adjustable cracking pressure, the literature describes external adjustment with a lock wire feature, and spring kits are listed separately by pressure band. Give us the set pressure you need, and the spring band and set point are confirmed per order.
Where the Code Line Sits
An instrumentation relief valve is not a substitute where an ASME code-stamped safety valve is required. ASME states that Section VIII Division 1 covers pressure vessels operating above 15 psig and includes the rules for the U, UM and UV certification marks; the Superlok® pages carry no such mark. For placement, keep the device where nothing can close it off from the section it protects, as the note on root valve vs isolation valve explains. Lower set points are covered by the SRVL series, and the wider range is on the relief valves page.
Questions
Does cracking pressure mean set pressure here?
In the PDF, set pressure is the upstream pressure at which the first indication of flow occurs. Confirm how the listing uses cracking pressure for your order.
Which spring covers 3500 psig?
The white band, 3000 to 4000 psig. Springs are kits named by designator, so state the set point on the order.
Is a PTFE seat standard?
One parts table in the PDF lists it and the other does not, and the catalog page does not mention a seat. Seat and O-ring are confirmed per order.
How does this compare with a check valve?
A check valve also has a cracking pressure but opens to allow flow in one direction. The comparison is in check valve cracking pressure.
Setting a high pressure relief point?
Send the fluid, set pressure, temperature and connection, and we will confirm what is listed.
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Sources
- U.S. Department of Energy, “DOE Fundamentals Handbook, Mechanical Science, Module 4, Valves,” DOE-HDBK-1018/2-93, January 1993, as reproduced by PDH Online. Supports the spring and fluid force description, the seating finish statement and the elastomer temperature and pressure caution. pdhonline.com
- ASME, “BPVC Section VIII Division 1,” product page, 2025 edition listing. Supports the scope above 15 psig and the U, UM and UV marks. asme.org
- Superlok® North America, high pressure relief valve catalog page (manufacturer of record). Supports the cracking range, 6000 psig maximum, 4.8 mm orifice, seal and material fields and the adjustable cracking pressure. superloknorthamerica.com
- Superlok® North America, spring kit page (manufacturer of record). Supports the separate spring kits and the band boundaries. superloknorthamerica.com/catalog-products/srvh-springs-for-srvh-high-pressure-relief-valves/
- Superlok® North America, relief valves category page (manufacturer of record). Supports the NBR temperature range and the note that seals are not tied to valves. superloknorthamerica.com
- Superlok® North America, relief valve PDF (manufacturer of record). Supports the spring band table, the set pressure definition, the 5 percent repeatability statement and the two parts tables. superloknorthamerica.com/wp-content/uploads/2023/11/superlok-relief-valve.pdf
Technical note: The DOE handbook establishes how a spring-loaded relief valve works in general and says nothing about these models. The Superlok® pages are the source for the ratings, spring bands and materials; spring, seat and seal are confirmed per order. The area and force figures are our arithmetic and assume sealing at the full orifice. No source gives relieving capacity, reseat pressure, blowdown, flow rate or a temperature range for the series. Grade and rating confirmed per order.
Trademark disclaimer: Superlok® is a registered trademark. ASME, the U.S. Department of Energy and PDH Online are named only to identify sources and belong to their owners. Cross-references are made by form, fit, and function only.