The Valve,safety Relief, cataloged under National Stock Number 4820-01-261-5644, is classified within Federal Supply Class 4820 (Valves, Nonpowered) of the Valves group. Government technical data includes 21 specifications, cited from the U.S. Government catalog. 3 additional reference documents (drawings, advisory and superseded references) are recorded in the U.S. Government catalog. 1 item shares a part number with this NSN in the catalog (possible match — not a government interchangeability claim). Current acquisition status: Active.
| Parameter | Value |
|---|---|
| NSN | 4820-01-261-5644 |
| Item Name | Valve,safety Relief |
| FSC / FSG | 4820 / 48 — Valves, Nonpowered |
| Status | ACTIVE |
| Flow Control Device | POPPET |
| Furnished Items and Quantity | 1 DEFLECTOR CAP |
| Connection Style | PLAIN (PIPE) FIRST END |
| Connection Type | THREADED EXTERNAL PIPE FIRST END |
| Style Designator | STRAIGHT THRU |
| Operating Pressure | 200.0 POUNDS PER SQUARE INCH (PSI) MAXIMUM SINGLE RESPONSE LBS |
| Adjustable Pressure Range | +0.0 TO 200.0 POUNDS PER SQUARE INCH LBS |
| Thread Direction | RIGHT-HAND FIRST END |
| Nominal Thread Size | 0.500 INCHES FIRST END IN |
| Maximum Operating Temp | -40.0 FAHRENHEIT FIRST RESPONSE DEGF |
| Maximum Operating Temp | 250.0 FAHRENHEIT SECOND RESPONSE DEGF |
| Media for Which Designed | ACETYLENE SECOND RESPONSE |
| Media for Which Designed | HYDROGEN FIFTH RESPONSE |
| Media for Which Designed | AMMONIA, GASEOUS THIRD RESPONSE |
| Media for Which Designed | AIR FIRST RESPONSE |
| Media for Which Designed | REFRIGERANT 12 FOURTH RESPONSE |
| Material | COPPER ALLOY BODY |
| Material | RUBBER PACKING |
| Thread Series Designator | NPT FIRST END |
| Opening Pressure Setting | 40.0 POUNDS PER SQUARE INCH LBS |
| Valve Operation Method | AUTOMATIC |
| Acquisition Status | ACTIVE |
| DEMIL Code | DEMIL Q — CCL Item — Commerce Control List |
| Hazard | No hazard code in the DLA record (HMIC N) |
| Criticality Code | X |
| Reference | Meaning |
|---|---|
| 3255546-1 | C/1 Advisory reference — outside the item-of-supply concept Naval Sea Systems Command |
| 3255546 | 7/2 Vendor item drawing reference Navair and Navsea Managed Original Design Activity Dwg Not Material/parts Supplier |
| D559B-4M-40 | 3/2 Design control — primary reference U.S. Government activity |
NSN 4820-01-261-5644 is a Valve,safety Relief, classified under FSC 4820, Valves, Nonpowered. Status: active.
1 possible match (shared part number, not a government interchangeability claim): 4820-01-320-6004. Verify interchangeability with system specifications before substitution.
Key specifications for 4820-01-261-5644: Flow Control Device: POPPET; Furnished Items and Quantity: 1 DEFLECTOR CAP; Connection Style: PLAIN (PIPE) FIRST END; Connection Type: THREADED EXTERNAL PIPE FIRST END. 21 specifications are documented in the U.S. Government catalog.
No hazard code in the DLA record (HMIC N). Hazard information on this page is shown exactly as it appears in the DLA record.
NSN 4820-01-261-5644 has DEMIL Code Q. Demilitarization may be required before disposal or transfer to non-military entities.
U.S. Government catalog: edition PUBLOGDVD v12.0.0 (OCT 2026), edition date 2026-10-01, retrieved 2026-10-16.
U.S. Government catalog: edition PUBLOGDVD v12.0.0 (OCT 2026), edition date 2026-10-01, retrieved 2026-10-18.