Chapter 6: Page 1

There are two types of leakage: external and internal. Because internal leakage (i.e., inside components) is a complex topic all its own, this discussion is limited to troubleshooting external leakage. Monitoring external leakage is fairly easy (Figure 6.1); stopping it is not difficult, but preventing its recurrence may be a challenge that may require piping and/or circuit changes. Every industry has been plagued by piping system leakage. This condition exists at all levels of industry between the drawing board and/or computer aided design and computer aided manufacturing (CAD-CAM) and the scrap dealer:

At the original equipment manufacturers (OEM) level the delivery of new units is frequently delayed because of fluid system leakage.
At the dealer level-sales are lost when oil is observed dripping from the unit onto the showroom floor.
At the user level-costly work stoppages occur to replace blown 0-rings and retighten fittings.

The basic causes of fluid system leakage are:

human error
lack of quality control
poor protection of components in handling
difficult if not impossible to reach fitting connections
lack of education
poor selection of materials
improper design of piping or pipe routing

FIND THE LEAK

Pinpoint the leak location; make sure that the leak is not up higher and draining down:
- wash down leakage area.
- watch for the leak to show.
- place a paper towel above the connection, it will catch any fluid dropping from above.
Determine if the leak is at a valve spool, rod packing, motor or pump shaft, cracked casting, piping joint, or hose or tube. Seepers or weepers can be hard to locate.

Figure 6.1 Troubleshooting procedures
for hydraulic leakage problems. Courtesy
of Vickers, Incorporated.

Left: The troublesome NPT thread. Right: The dry seal thread did not cure all leakage problems and, in fact, created some new problems

TAPERED PIPE THREAD

All other factors notwithstanding, the greatest contributor to external leakage has been the tapered pipe thread. When components with pipe threads are assembled, the threads leave a space shaped like a conical helix. This helix is a ready-made leakage path (Figure 6.2). Various methods have been used to eliminate this leakage path-from mechanically crushing the threads to using sealing tapes or other sealant materials-but results are not always satisfactory, particularly when connections must be opened and remade. A redesigned taper pipe thread called the dry seal eliminated the helix and crushed the thread when engaged (Figure 6.3). Manufacturers found that when cast iron components with dry seal threads were tested by the manufacturer prior to shipping the dry seal thread form in the relatively soft body was damaged and new components often leaked when installed on the machine. A taper pipe thread when over-tightened may split the casting or cause distortion which causes valve malfunctions. The solution is not to use NPT or NPTF threads at all. Substitute straight thread and/or flange connections that are leak free.

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