S-500 THREADED QUICK
OPENING CLOSURE
Stark Solutions
The Stark S-500 Threaded Quick Opening Closure is the industry’s most widely used closure style, refined by Stark for robust, cost-effective access to pressure vessels and pipeline barrels. A threaded cap rotates into the hub until the flat faces meet metal-to-metal, fully compressing the O-ring groove for a reliable seal.
Its key safety feature is a modified ACME thread: once the seal is broken, over 90 percent of the threads stay engaged, so the cap cannot dislodge if residual pressure remains. A Pressure Alert Valve warns of that pressure and must be removed before the cap can rotate, and a bidirectional hinge lets the cap open left or right.
Available from 2″ through 52″ (DN50 to DN1300) in pressure series 150 through 2500, the closure is certified to ASME B31.3, B31.4, B31.8, and CSA Z662 Cat. II, and is offered U-Stamped when required. NACE MR0175-compliant materials and a -50°F to 400°F rating suit sour and wide-temperature service, with anti-hammering opening tools scaled to each size.
Typical Applications:
Pipeline pig launcher and receiver access, filter and separator vessel access, quick access to pressure vessels, gathering and transmission barrels, and sour (NACE) service.
Key Features
- Threaded quick opening design
- Diameters 2″ through 52″ (DN50 to DN1300)
- Pressure series 150 to 2500
- Modified ACME thread, 90%+ engagement after seal break
- Flat metal-to-metal sealing surface
- Industry-standard O-ring seal
- Pressure Alert Valve (PAV) per ASME BPVC VIII Div. 1
- Bidirectional hinge, opens left or right
- ASME B31.3, B31.4, B31.8, CSA Z662 Cat. II certified
- ASME BPVC VIII Div. 1, U-Stamp compliant cap
- NACE MR0175-compliant material
- -50°F to 400°F (-45°C to 204°C)
- Anti-hammering opening tools by size
- Square boss, lug wrench, or ratchet tool
- Double roller hinge on 16″ and larger
- Integrated hinge bearings on 24″ and larger
PERFORMANCE ADVANTAGES
Why the Stark S-500 Closure Performs Where It Counts
THREAD ENGAGEMENT THAT HOLDS
UNDER PRESSURE
The modified ACME thread keeps over 90 percent engagement even after the seal is broken, so the cap cannot dislodge from the hub if pressure remains in the line. That single feature removes the most dangerous failure mode of a threaded closure.
TWO-STEP PRESSURE SAFETY
The Pressure Alert Valve warns of residual pressure and must be physically removed before the cap can rotate, forcing a deliberate check before opening. That builds ASME-compliant safety into the operating sequence rather than relying on procedure alone.
FLAT-FACE METAL-TO-METAL SEAL
As the cap tightens, the flat sealing faces of cap and hub meet metal-to-metal and fully compress the O-ring groove for a reliable seal across all sizes. An industry-standard O-ring keeps replacement parts readily available and inexpensive.
OPERATION WITHOUT HAMMERING
Size-matched opening tools, from a square boss and lug wrenches to a ratchet tool on larger closures, deliver leverage that eliminates hammering on the cap lugs. Double roller hinges and integrated bearings on larger sizes further improve control and ease of operation.