Some fasteners cannot be classified as rivets, turnlocks, or threaded fasteners. Included in this category are connectors, couplings, clamps, taper and flat-head pins, snap rings, studs, and heli-coil inserts.

FLEXIBLE CONNECTORS AND COUPL-INGS. A variety of clamping devices are used in connecting ducting sections to each other or to various components. Whenever lines, components, or ducting are disconnected or removed for any reason, you should install suitable plugs, caps, or coverings on the openings to prevent the entry of foreign materials. You should also tag the various parts to ensure correct reinstallation. You should exercise care during handling and installation to ensure that flanges are not scratched, distorted, or deformed. Flange surfaces should be free of dirt, grease, and corrosion. The protective flange caps should be left on the ends of the ducting until the installation progresses to the point where removal is necessary. In most cases it is mandatory to discard and replace seals and gaskets. You should ensure that seals and gaskets are properly seated and that mating and alignment of flanges are fitted. This will prevent the excessive torque required to close the joint, which imposes structural loads on the clamping devices. Adjacent support clamps and brackets should remain loose until installation of the coupling has been completed.

Figure 2-12.Dzus fastener.

Some of the most commonly used plain-band couplings are shown in figure 2-13. When you install a hose between two duct sections, the gap between the duct ends should be a minimum of 1/8 of an inch and a maximum of 3/4 of an inch. When you install the clamps on the connection, the clamp should be 1/4 of an inch from the end of the connector. Misalignment between the ducting ends should not exceed 1/8 of an inch.

Marman clamps are commonly used in ducting systems and should be tightened to the torque value indicated on the coupling. Tighten all couplings in the manner and to the torque value specified on the clamp or in the applicable maintenance instruction manual.

When you install flexible couplings, such as the one shown in figure 2-14, the following steps are recommended to assure proper security:

1. Fold back half of the sleeve seal and slip it onto the sleeve.

Figure 2-13.Flexible line connectors.

Figure 2-14.Flexible line coupling.

Figure 2-15.Installation of rigid line couplings.

2. Slide the sleeve (with the sleeve seal partially installed) onto the line.