The Valve,safety Relief, cataloged under National Stock Number 4820-00-451-0570, is classified within Federal Supply Class 4820 (Valves, Nonpowered) of the Valves group. The manufacturer of record is Ausco Inc. Government technical data includes 29 specifications, cited from the U.S. Government catalog. The record lists 1 manufacturer part number for this item, enabling identification through both NSN and commercial part number lookups. 1 additional reference document (drawings, advisory and superseded references) is recorded in the U.S. Government catalog. 1 item shares a part number with this NSN in the catalog (possible match — not a government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 | 4820-00-451-0570 |
| Primary Part Number | H555 |
| Item Name | Valve,safety Relief |
| FSC / FSG | 4820 / 48 — Valves, Nonpowered |
| Manufacturer | Ausco Inc |
| Status | ACTIVE |
| Flow Control Device | POPPETPOPPET |
| Connection Style | EXTERNAL SEAT FOR GASKET SEAL (BOSS) SECOND ENDEXTERNAL SEAT FOR GASKET SEAL (BOSS) SECOND END |
| Connection Style | GASKET SEAL(BOSS) FIRST ENDGASKET SEAL(BOSS) FIRST END |
| Connection Type | THREADED INTERNAL BOSS FIRST ENDTHREADED INTERNAL BOSS FIRST END |
| Connection Type | THREADED EXTERNAL BOSS SECOND ENDTHREADED EXTERNAL BOSS SECOND END |
| Material Document and Classification | AMS 5643 MFR REF 2ND MATERIAL RESPONSE FLOW CONTROL DEVICE |
| Material Document and Classification | AMS 5643 MFR REF 2ND MATERIAL RESPONSE FLOW CONTROL DEVICEQQ-S-764,TYPE 303-CANCELED FED SPEC 3RD MATERIAL RESPONSE SEAT |
| Material Document and Classification | QQ-S-764,TYPE 303-CANCELED FED SPEC 3RD MATERIAL RESPONSE SEATQQ-S-764,TYPE 303-CANCELED FED SPEC 1ST MATERIAL RESPONSE BODY |
| Nominal Outside Diameter Tube Accommodated | 0.500 INCHES SECOND END IN |
| Nominal Outside Diameter Tube Accommodated | 0.500 INCHES SECOND END0.500 INCHES FIRST END IN |
| Operating Pressure | 35.0 POUNDS PER SQUARE INCH (PSI) MAXIMUM SINGLE RESPONSE LBS |
| Features Provided | PRESSURE TIGHT OUTLET SIDEPRESSURE TIGHT OUTLET SIDE |
| Bonnet Type | PACKING RETAININGPACKING RETAINING |
| Thread Direction | RIGHT-HAND SECOND ENDRIGHT-HAND SECOND END |
| Thread Direction | RIGHT-HAND FIRST ENDRIGHT-HAND FIRST END |
| Nominal Thread Size | 0.750 INCHES SECOND END0.750 INCHES SECOND END IN |
| Nominal Thread Size | 0.750 INCHES FIRST END0.750 INCHES FIRST END IN |
| Maximum Operating Temp | 275.0 FAHRENHEIT SINGLE RESPONSE275.0 FAHRENHEIT SINGLE RESPONSE DEGF |
| Disk Loading Method | SPRINGSPRING |
| Media for Which Designed | HYDRAULIC FLUID, MINERAL BASE SINGLE RESPONSE |
| Thread Class | 3A SECOND END3A SECOND END A |
| Thread Class | 3B FIRST END3B FIRST END |
| Thread Quantity Per Inch | 16 FIRST END16 FIRST END |
| Thread Quantity Per Inch | 16 SECOND END16 SECOND END |
| Material | STEEL COMP 630 FLOW CONTROL DEVICE |
| Material | STEEL COMP 303 SEATSTEEL COMP 303 BODY |
| Material | STEEL COMP 630 FLOW CONTROL DEVICESTEEL COMP 303 SEAT |
| Thread Series Designator | UNF SECOND END |
| Thread Series Designator | UNF SECOND ENDUNIFIED NATIONAL JOINT FINE (UNJF) FIRST END |
| Acquisition Status | ACTIVE |
| DEMIL Code | DEMIL A — No Demilitarization Required |
| Hazard | No hazard code in the DLA record (HMIC N) |
| Criticality Code | X |
| Part Number | Manufacturer |
|---|---|
| H555 PRIMARY | Ausco Inc (USA) |
| Reference | Meaning |
|---|---|
| 65651-09106-102 | 7/2 Vendor item drawing reference Sikorsky Aircraft Corporation Dba Sikorsky Aircraft Corp |
NSN 4820-00-451-0570 is a Valve,safety Relief, manufactured by Ausco Inc, classified under FSC 4820, Valves, Nonpowered. Status: active.
NSN 4820-00-451-0570 has 1 manufacturer part number on file: H555 (Ausco Inc).
1 possible match (shared part number, not a government interchangeability claim): 5310-00-857-5559. Verify interchangeability with system specifications before substitution.
Key specifications for H555: Flow Control Device: POPPETPOPPET; Connection Style: EXTERNAL SEAT FOR GASKET SEAL (BOSS) SECOND ENDEXTERNAL SEAT FOR GASKET SEAL (BOSS) SECOND END; Connection Style: GASKET SEAL(BOSS) FIRST ENDGASKET SEAL(BOSS) FIRST END; Connection Type: THREADED INTERNAL BOSS FIRST ENDTHREADED INTERNAL BOSS FIRST END. 29 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.
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.