The compression fitting has a flared metal tube or a compression fitting that is surrounded by a threaded flare nut. Because the tube is flared or has a compression fitting installed, the threaded flare nut cannot be removed from the line and is considered part of the assembly.
Compression fittings are most often used when a pressure line attaches to an assembly, much like the fluid lines found at the brake master cylinder or on the inlet fuel line for the firewall-mounted fuel filter found on some Toyota Camry and Avalon models.
The compression fitting does not have a gasket or seal, rather it uses the threaded flare nut to seal the flared end of the line or a compression fitting on the line to the assembly. The flared end of the fuel line or the compression fitting is sealed between the component and the flare nut.
A compression fitting is most often found where the fluid in the line is under considerable pressure.
The flare nut is one of two types:
To disconnect a fuel line using a compression fitting:
- Hold the component that the flare nut is threaded onto securely, and using a flare nut type wrench, loosen the flare nut.
- Installation is the reverse of the removal procedure.
- When attaching a flare nut on the high pressure line, follow the below steps;
- Apply a light oil to the flare nut before installation. This will help insure that the threads mesh properly.
- Always start the nut on to the line by hand to prevent possible cross-threading.
- Tighten the flare nut using only a multi-sided flare nut wrench which was designed specifically for the job. Regular open ended wrenches, pliers, vise grips, etc. will only damage the nut.
- Torque the line nut to 21 ft. lbs. (28 Nm).