Quick-disconnect couplings provide a means of quickly disconnecting a line without the loss of hydraulic fluid or entrance of air into the system. Each coupling assembly consists of two halves, held together by a union nut. Each half contains a valve, which is held open when the coupling is connected. This action allows fluid to flow in either direction through the coupling. When the coupling is disconnected, a spring in each half closes the valve, preventing the loss of fluid and entrance of air. The union nut has a quick-lead thread that permits connecting or disconnecting the coupling by turning the nut. The amount the nut must be turned varies with different styles of couplings. For one style, a quarter turn of the union nut locks or unlocks the coupling. For another style, a full turn is required. Some couplings require wrench tightening; others are connected and disconnected by hand. Some installations require that the coupling be safetied with safety wire; others do not require any form of safetying. Because of these individual differences, all quick disconnects should be installed in accordance with the instructions in the applicable MIM. The series 145 and 155 (Aeroquip) couplings make up one type of quick-disconnect coupling found on naval aircraft. These couplings may be identified by the part number (145 or 155) stamped on the face of the union nut.

Each quick-disconnect coupling consists of two halves, referred to as S1 half and S4 half. See figure 2-39. When disconnected, the union nut remains with the S1 half. The S4 half has a mounting flange for attaching to a bulkhead or other structural member of the aircraft.

All parts referred to in the following paragraphs are identified in figure 2-39. The two halves of the coupling may be connected by placing the tubular valve (1) within the protruding nose (6) of the mating half, and rotating the union nut in a clockwise direction. The union nut must be rotated until its teeth (5) fully engage the lock spring (8). A properly tightened coupling will have compressed the lock spring until a 1/16-inch minimum gap exists between the inside lip of the spring retainer fingers and the spring plate. Figure 2-40 shows the coupling both properly connected and improperly connected. The locking action may be followed by referring to figure 2-39. Positive locking is assured by the locking spring (8) with teeth, which engage ratchet teeth on the union nut (5) when the coupling is fully connected. The lock spring automatically disengages when the union nut is unscrewed. An O-ring packing (3) seals against leakage as the coupling halves are joined. Positive opening of the valves occurs as the halves are connected. 

When the coupling halves are joined, the protruding nose (6) of the S4 half contacts the sleeve (4) of the S1 half. Simultaneously, the head of the tubular valve (1) contacts the face of the poppet valve (7), thus preventing air from entering the system. Tightening the union nut pulls the coupling halves together. This causes the nose of the S4 half to push the sleeve into the S1 half, uncovering the ports to the tubular valve. At the same time, the head of the tubular valve depresses the poppet valve. 

When the coupling halves are fully connected, the sleeve and poppet valve have reached the positions shown in the left-hand view of figure 2-40. The nose of the S4 half has engaged the O-ring packing of the S1 half, providing a positive seal.

Figure 2-40.-Quick disconnects properly and improperly connected.

Figure 2-41.-Series 320 (Aeroquip) quick disconnect. 

NOTE: Modified union nuts may be identified by the letter C preceding the part number on the nut. On these modified union nuts, a wrench may be used to assist in tightening the coupling. Torque values for the various size couplings may be found in the aircraft MIM, and should be strictly complied within all instances.

A newer type of quick-disconnect coupling is the series 3200 (Aeroquip). This is an improved version and is simple to operate. This series is designed for use in hydraulic systems up to 3,000 psi operating pressure. Figure 2-41 shows the quick disconnect in both the disconnected and connected positions. To connect, align the tabular valve of the hose-attaching half with the recess in the bulkhead-coupling half. The nut is then brought forward to engage the threads, and rotated in a clockwise direction until the hex nut engages the hex on the coupling body. This may be done in one continuous turn of the union nut, about one-quarter of a revolution. The quick-lead Acme thread allows the coupling to be connected by hand, against pressures up to 300 psi.

The connection may be inspected by three different methods as follows: If the nut can be turned by hand in a clockwise direction, the coupling is not locked. A slight tug on the hose will separate the halves if the couplings are not locked. Inspect the locking male hex on the bulkhead coupling half; if the coupling is not connected, the red male hex of the bulkhead half will be visible.