Causes of leakage:

1. Elbows loosen up after short service.
2. O-ring leakage after short service.
3. 0-ring leakage after long service.
4. Instant leakage upon start up.

Causes may be either human error or faulty parts!

(Figure 6.10). A lubricated seal will move into the pocket as intended in the D direction. An unlubricated seal may move in the C direction.
(Figure 6.11):An unlubricated seal moving in the C direction will be pinched as the jam nut is tightened.

Cures:

1) Replace 0-ring seals and start over.

• Jam nut and washer must be to the back side of the smooth portion of the elbow adapter.
• It is very important to lubricate the O-ring.
• Thread into port until washer bottoms onto spot face. (Make certain that the spot face is large enough for the washer or the hex of the straight adapter.
• Position elbows by backing up the adapter.
• Tighten jam nut.

2) Lubrication is essential for the O-ring.

• Fitting engaged to point where O-ring touches face of boss (Figure 6.10). Lubrication on 0-ring permits it to move in direction D.
• When 0-ring and boss are dry, rotary motion of assembly can cause friction and 0-ring can move in direction C.
• Jam nut and washer cannot bottom fully if the 0-ring is between the washer and the face of the boss (Figure 6.11).
• The compressed elastomer between the washer and the boss face will cold flow out from compression and the fitting will be loose and usually leak (Figure 6.12).
• A properly assembled fitting will result in the washer securely containing the elastomeric seal with the face of the jam nut parallel with the washer and spot face (Figure 6.13).

This design depends on compression or squeeze of the O-ring, the jam nut, washer, face of boss, and the body threads to hold the elbow tightly in position.

3. If some elbows loosen up and others do not:

• If the jam nut loosens, the whole fitting becomes loose.
• SAE permits a chamfer on both sides of the jam nut (Figure 6.14).
• When both sides of nut are chamfered, there is much less compression area to squeeze onto the washer when tightened (Figure 6.15).
• When the washer side of the jam nut is left flat, the contact and squeeze area is greatly increased and makes a big difference (Figure 6.16).

If the problem persists consider a jam nut that is flat on the washer side with the jam nuts and retaining washers prepositioned to the far side of the smooth area to help eliminate human error.

The sectional view of a typical mobile-type directional valve shows the straight thread, pocket for the O-ring, and spot face in the work port (Figure 6.17). The plug used to secure the load hold check also uses the straight thread and 0-ring configuration. The supply line to the valve and the return to tank may be fitted with a four bolt flange connection, typically in sizes of one-inch or larger.