Figure 3-44. - T-seals.

designed because of the following advantages of such a system:

Simplicity

Ruggedness

Low cost

Ease of installation

Ease in maintenance

No adjustment required

No critical torque in clamping

Low distortion structure

Small space requirement

Effectiveness over wide pressure and temperature ranges

O-rings are used in both static (as gaskets) and dynamic (as packing) applications. An O-ring has always been the most satisfactory choice of seals in static applications when the fluids, temperatures, pressure, and geometry permit.

Quad-Rings. - The quad-ring is very similar to the O-ring, the major difference being that the quad-ring has a modified square type of cross section, as shown in figure 3-45. Quad-rings are molded and trimmed to extremely close tolerances in cross-sectional area, inside diameter, and outside diameter. Quad-rings are ideally suited for both low pressures and extremely high pressures.

U-CUPS. - The U-cup (fig. 3-46) is a popular packing due to its ease of installation and low friction. U-cups are used primarily for pressures below 1,500 psi; but, they can be used for higher pressures with the use of backup rings. When more than one U-cup is installed, they are installed back to back or heel to heel. This back- to-back installation is necessary to prevent a pressure trap (hydraulic lock) between two packings.

Figure 3-45. - Quad-ring.

Figure 3-46. - Typical U-cup seal.

HYDRAULIC SYSTEM MAINTENANCE

Maintenance of a hydraulic system that is properly operated and cared for is a routine task. Maintenance usually consists of changing or cleaning filters and strainers, and occasionally adding or changing the fluid in the system. However, overheating, excessive pressure, and contamination can damage an improperly operated system.

Proper maintenance reduces your hydraulic troubles. By caring for the system using a regular maintenance program, you can eliminate common problems and anticipate special ones. These problems can be corrected before a breakdown occurs. 3-25