(3) Installation tolerances. These tolerances apply to tube end gap limits, and acceptable or nonacceptable
limits of the standard Permaswage union fitting.
The following instructions apply to union fittings, as in figure 4-87, shaped fittings, (elbows, tees, crosses,
and shaped reducers), as in figure 4-88; and separable fittings (MS and AN, male and female), as in figure
(a) For MAXIMUM tube end gap, the leading edge of the tube insertion mark must be In line with the outside
edge of the swaging tool latch.
(b) For MINIMUM tube end gap when using union and shaped fittings, the back edge of the tube insertion
mark must be In line with the outside edge of the latch.
(c) For MINIMUM tube end gap using separable fittings only, the tube is inserted until it is bottomed.
Acceptable tube insertion limits when using unions are shown in figure 4-90 detail A. Unacceptable limits
are shown In figure 4-90, detail B
4-10. Quick-Disconnect Couplings. Quick-disconnect couplings of the self-sealing type are used at various points in
all hydraulic systems. These couplings are Installed at locations where frequent uncoupling of lines is required for
inspection and maintenance. 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, allowing fluid to flow in either direction through the
coupling. When the coupling is disconnected, a spring in each half closes the valves, preventing loss of fluid and
entrance of air. The union nut has a quick-lead thread which permits the coupling to be connected or disconnected by
turning the nut. Various types of union nuts are used in hydraulic systems. For one type, a quarter-turn on the union nut
locks or unlocks the coupling For another type, a full turn is required Some couplings require wrench tightening, others
are connected and disconnected by hand Some installations require that the coupling be secured with safety wire; others
do not require any form of safetying. Because of these differences, all quick disconnects must be Installed In accordance
with the Instructions in the applicable maintenance manual. However, following are general guidelines for installation and
Installation. When installing a coupling, the coupling can be fully connected by hand The external shape of the
union nut sleeve is such that it can be tightened by a wrench. The union nut must be tightened until It can no longer
Inspection. The quick-disconnect coupling will be Inspected as follows:
(1) Inspect union nut for tightness and security.
(2) Inspect coupling for leaks when pressure is applied.
(3) Actuate affected component to ensure free flow through the coupling.