Eaton 155S5-4D - Size -4 Self-Sealing Hydraulic Coupling

The Eaton 155S5-4D is the Style I, size -4 hose-attaching half of the Aeroquip 145 and 155 Series self-sealing hydraulic quick-disconnect coupling. Engineered for petroleum-based hydraulic systems using MIL-H-5606 or MIL-H-83282 fluid, this coupling half allows aircraft hydraulic lines to be connected and disconnected quickly without fluid loss or air ingestion — a critical capability for line maintenance, component changeouts, and ground servicing operations.

Originally produced under the Aeroquip brand and now part of Eaton's Aerospace Group portfolio, the 155S5-4D mates with the bulkhead-mounting half TB155S4-4D and conforms to the AS4395 flared end-fitting standard. The coupling uses a quick-lead blunt-start thread that connects and disconnects by hand with a simple turning motion. During connection, ratchet teeth on the inner sleeve of the union nut engage a unique lock spring assembly that provides positive locking under extreme vibration, and the lock automatically releases during disconnection.

Key Features

• Style I, size -4 hose-attaching half for 145/155 Series self-sealing couplings
• Compatible with MIL-H-5606 and MIL-H-83282 petroleum-based hydraulic fluid
• Self-sealing design prevents fluid loss and contamination during disconnection
• AS4395 flared end-fitting standard for hose-side termination
• Quick-lead blunt-start thread for hand connection without tools
• Lock spring assembly provides positive locking under high vibration
• Mates with bulkhead-mounting half TB155S4-4D (sold separately)
• Fully interchangeable with all fielded Aeroquip 145/155 Series hardware

Specifications

• Manufacturer: Eaton (Aeroquip Aerospace Group)
• Part Number: 155S5-4D
• Type: Self-Sealing Coupling, Hose-Attaching Half
• Series: 145/155 Series
• Style: Style I
• Size: -4
• End-Fitting Standard: AS4395 (Flared)
• Fluid Compatibility: MIL-H-5606, MIL-H-83282 (Petroleum-Based Hydraulic)
• Mating Bulkhead Half: TB155S4-4D
• Phosphate-Ester Equivalent: 015567S5-4D (for Skydrol systems)
• CAGE Code: 00624

Compatible Dust Cap and Plug

To protect the coupling halves when disconnected, use the dust cap on the bulkhead half and the dust plug on the hose-attaching half:

• Dust Cap: Eaton 155S7-5D
• Dust Plug: Eaton 155S9-5D

Note: Union nut, lock springs, flange, dust plug, and dust cap size 5 is used on coupling half sizes 4 and 5.

Applications

The 155S5-4D is used throughout military and commercial aircraft hydraulic systems wherever a size -4 self-sealing quick disconnect is required. Typical applications include flight control systems, landing gear hydraulics, brake systems, hydraulic test stand connections, and component-level servicing where rapid disconnection without fluid loss is essential. MROs, FBOs, repair stations, OEMs, and military maintenance shops rely on the 145/155 Series for its proven vibration resistance, hand-operable design, and broad interchangeability across legacy and current aircraft platforms.