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Brand: Swagelok
Swagelok SS-RL4S8 Low-Pressure Relief Valve, 1/2 in. Tube
Description
The Swagelok SS-RL4S8 is a low-pressure proportional relief valve with 1/2 in. tube fitting ends. Its set pressure is adjustable from 10 to 225 psig (0.7 to 15.5 bar) with one factory-installed spring, so it protects low-pressure gas, vent and utility lines without a spring change. The 316 stainless steel body and FKM seal handle inlet pressures to 300 psig (20.6 bar). It is the right relief for pressure-sensitive instruments, glass or plastic lined equipment and low-pressure sampling systems.
Technical specifications
| Parameter | Specification |
|---|---|
| Part number | SS-RL4S8 |
| Description | Low-pressure (RL4) proportional relief valve, no handle |
| Series | RL4 |
| Body material | 316 stainless steel |
| Connections | 1/2 in. Swagelok tube fitting inlet and outlet |
| Fully open orifice | 0.25 in. (6.4 mm) |
| Set pressure range | 10 to 225 psig (0.7 to 15.5 bar), single spring |
| Inlet working pressure | 300 psig (20.6 bar) |
| Outlet working pressure | 225 psig (15.5 bar) |
| Seal material | Fluorocarbon FKM |
| Resealing at 10 to 20 psig set | Minimum 50 percent of set pressure |
| Resealing at 175 to 225 psig set | Minimum 91 percent of set pressure |
| Cleaning | Standard cleaning and packaging SC-10 |
One spring for the whole range
On the high-pressure R3A and R4 valves you pick one of several springs for the pressure band. The RL series has one spring for the entire 10 to 225 psig range, already installed, so the set pressure is changed by adjusting the cap. This keeps stocking simple but means resealing performance depends on where in the range you set it: the catalog requires only 50 percent resealing pressure for 10 to 20 psig settings and 91 percent for 175 to 225 psig.
Valves can be ordered factory-set, for example with the -SET designator, instead of set on site.
Back pressure matters here
Unlike the high-pressure valves, system back pressure raises the set pressure of the RL series. The catalog gives a compensation rule: multiply the back pressure by 0.8 and subtract it from the desired set pressure, then pre-set the valve with the back pressure at atmospheric. For a 120 psig target with 40 psig back pressure, pre-set it at 88 psig. If your discharge is piped to a header, apply this correction.
Outlet working pressure is limited to 225 psig and should not exceed inlet pressure.
Limits and ordering
Like every Swagelok R series valve, this is a proportional relief valve and not an ASME code safety valve or a PED safety accessory. SS-RL4S8 is the 1/2 in. size; SS-RL4S12MM is 12 mm, and the 1/4 in. SS-RL3S4 belongs to the RL3 series. Replacement spring and seal kits are catalog items. Quote the full code and the set pressure you need.
Maximum set pressure falls as temperature rises for each seal, so check the catalog for high-temperature service.
Related Swagelok products: Swagelok SS-RL3S4 Low-Pressure Proportional Relief Valve, Swagelok SS-4R3A1 Proportional Relief Valve, MNPT x 1/4 in. Tube, Swagelok SS-4R3A5 Proportional Relief Valve, MNPT x FNPT, Swagelok R3A Series High-Pressure Proportional Relief Valve, Swagelok SS-R4S8 Proportional Relief Valve, 1/2 in. Tube and Swagelok SS-4R3A5-RT Proportional Relief Valve, 1/4 in. ISO.
Documents and quotation
Official reference attached: Swagelok proportional relief valves R series catalog MS-01-141 (EN). Send us SS-RL4S8 with the quantity and any certification or option you need, and a quotation follows once the request is matched to the document. We supply as an independent company in Muscat.
Before ordering, please confirm the part number, size and connection against the attached document, as nearby codes differ by one character. Related items: product category.
Datasheets & Documents
- Catalog Swagelok proportional relief valves R series catalog MS-01-141 (EN) Download
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About brand
Swagelok is the American maker of tube fittings and small-bore valves, best known for its two-ferrule compression tube fitting. Fred A. Lennon and Cullen B. Crawford founded it in Cleveland, Ohio, in July 1947 as Crawford Fitting Company to make that fitting. Lennon bought the whole business and the patent in 1948, and the company has been based in Solon, Ohio, since the mid-1960s.
Seven Star LLC is an independent supplier in Muscat. We list Swagelok tube fittings, needle, ball, check, relief and metering valves, filters, regulators and sample cylinders, and supply them for instrument tubing and analyser systems in Oman and the GCC by exact part number.
Swagelok company profile
| Established | July 1947, Cleveland, Ohio, as Crawford Fitting Company |
|---|---|
| Founders | Fred A. Lennon and Cullen B. Crawford; Lennon bought out Crawford in 1948 |
| Headquarters | Solon, Ohio, since the mid-1960s |
| Product families | Tube fittings and adapters, face seal fittings, needle, ball, plug, check, relief and diaphragm valves, filters, regulators, quick-connects, sample cylinders and hoses |
Milestones
- 1947: Fred A. Lennon and Cullen B. Crawford found Crawford Fitting Company in Cleveland in July.
- 1948: Lennon buys out Crawford.
- Mid-1960s: Headquarters move to Solon, Ohio.
Swagelok products we list
| Family | Models | Typical use |
|---|---|---|
| Tube fittings | Overview, SS-810-6 union, SS-810-3 tee, SS-810-9 elbow, SS-810-4 cross, SS-810-1-8 male connector, SS-810-7-8 female connector, SS-810-61 bulkhead, SS-12M0-6 metric union, VCR face seal | Leak-tight connections on instrument and process tubing |
| Needle and metering valves | SS-1RS4, SS-1RF4, SS-18RF6, SS-6NBS6, SS-20VS4, SS-4MG | Isolation and fine flow adjustment on instrument lines and sample systems |
| Ball and plug valves | 40G, 40GX 3-way, 60 Series, 83 Series, P4T plug | Quick quarter-turn shut-off and switching |
| Check, relief and sealed valves | SS-4C-1, CH, R3A, RL3, SS-4BK bellows, SS-DLS4 diaphragm | Backflow prevention, overpressure relief and leak-free sealing for toxic or high-purity media |
| Filters, regulators, sampling | SS-4F-2, SS-4TF-7, KPR regulator, sample cylinders, QC quick-connects | Analyser sample conditioning and gas or liquid sampling |
A Swagelok part number can be read directly. In SS-810-6, "SS" is 316 stainless steel, "810" means a 1/2 in. tube fitting (8 sixteenths of an inch, 10 series), and "-6" is a union. A suffix such as "-8" adds a 1/2 in. NPT end, and "M0" marks metric tube, as in SS-12M0-6 for 12 mm. Tube fittings must be made up the same way every time: finger-tight, then 1 1/4 turns for most sizes. A gap inspection gauge confirms the fitting has been pulled up.
Where Swagelok products are used
In Oman and the GCC, Swagelok fittings and valves are used on instrument impulse lines, analyser sample systems, hydraulic and pneumatic control tubing, chemical injection and gas sampling in oil and gas, refining, petrochemical, power and laboratory installations.
Ordering Swagelok products: what we need
Send the full Swagelok part number (for example SS-810-6 or SS-1RS4), the material, and the tube size in inches or millimetres. For valves, add the end connections and any options. For sample cylinders, add the volume, pressure rating and end configuration.
Facts checked against Swagelok company history, October 2026.
Browse Swagelok products by category: Pipes & Fittings, Regulators, Fittings & Valves.
FAQ
Questions about the Swagelok SS-RL4S8 Low-Pressure Relief Valve, 1/2
Answers from our engineering team on installation, compatibility and integration.
01What set pressure range does SS-RL4S8 have?
10 to 225 psig (0.7 to 15.5 bar) with a single spring.
02How does back pressure affect it?
It raises the set pressure; multiply back pressure by 0.8 and subtract from the desired setting.
03What connection size?
1/2 in. Swagelok tube fitting at both ends.
04Is it a code safety valve?
No. It is a proportional relief valve, not certified to ASME or PED.
05How does it differ from SS-R4S8?
SS-R4S8 sets 50 to 1500 psig; SS-RL4S8 sets 10 to 225 psig.
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