O-rings are manufactured according to military specifications and are identified from the technical information printed on the O-ring package. See figure 2-44. The size of O-rings cannot be positively identified by visual examination without the use of special equipment. For this reason, O-rings are made available in individual, hermetically sealed envelopes labeled with all the necessary pertinent data.

NOTE: Colored dots, dashes, and stripes or combinations of dots and dashes on the surface of the O-ring are no longer used for identification of O-rings. O-rings still found with these color identification markings are NOT to be used in naval aircraft hydraulic systems or components and should be depleted from stock.

Figure 2-44 shows the information printed on O-ring packages that is essential to determine the intended use, qualifications, and age limitations. The manufacturers cure date is one of the more important printed items listed on the package. This cure date is denoted in quarters. For example, the cure date 2Q82 indicates that the O-ring was manufactured during the second quarter of 1982. Synthetic rubber parts manufactured during any given quarter are not considered one quarter old until the end of the succeeding quarter. Most O-ring age limitation is determined by this cure date, anticipated service life, and replacement schedule.

Age limitation of synthetic rubber O-rings is based on the fact that the material deteriorates with age. O-ring age is computed from the cure date. The term cure date is used in conjunction with replacement kits, which contain O-rings, parts, and hardware for shop repair of various components. O-ring cure dates also provide bases for O-ring replacement schedules, which are determined by O-ring service life. The service life (estimated time of trouble-free service) of O-rings also depends upon such conditions as use, exposure to certain elements, both natural and imposed, and subjection to physical stress. Operational conditions imposed on O-rings in one component may necessitate O-ring replacement more frequently than replacement of identical O-rings in other components. It is necessary to adhere to the recommended replacement schedule for each individual component. The age of O-rings in a spare part is determined from the assembly date recorded on the service or identification plate and/or on the exterior of the container. All O-rings over 24 months old should be replaced or, if nearing their age limit (24 months), should not be used for replacement.

Proper storage practices must be observed to prevent deformation and deterioration of rubber O-rings. Most synthetic rubbers are not damaged by several years of storage under ideal conditions. However, most synthetic rubbers deteriorate when exposed to heat, light, oil, grease, fuels, solvents,

Figure 2-45.Typical O-ring installation and removal tools.

thinners, moisture, strong drafts, or ozone (form of oxygen formed from an electrical discharge).

Damage by exposure is magnified when rubber is under tension, compression, or stress.

There are several conditions to be avoided, which include the following:

. Deformation as a result of improper stacking of parts and storage containers

. Creasing caused by a force applied to corners and edges, and by squeezing between boxes and storage containers

. Compression and flattening, as a result of storage under heavy parts

. Punctures caused by staples used to attach identification

. Deformation and contamination due to hanging the O-rings from nails or pegs

O-rings should be kept in their original envelopes, which provide preservation, protection, identification, and cure date. Contamination is caused by piercing the sealed envelopes to store O-rings on rods, nails, or wire hanging devices. Contamination may be caused by fluids leaking from parts stored above and adjacent to O-ring surfaces. Contamination can also be caused by adhesive tapes applied directly to O-ring surfaces. A torn O-ring package should be secured with a pressure-sensitive, moistureproof tape, but the tape must not contact the O-ring surfaces. O-rings should be arranged so the older seals are used first.