Crush installation is when an O-ring is crushed into a space having a cross-section different from that of a standard gland. O-ring volume is usually 90-95% gland volume. This use of an O-ring is a variation of the static seal. While it is an effective seal, the O-ring is permanently deformed and therefore generally considered non-reusable.
For more information, review our static crush seal grooves chart from the O-Ring Handbook (ORD 5700).
Reciprocating seals are a dynamic version of either a male radial or female radial O-ring design. In a reciprocating seal, there is relative reciprocating motion (along the shaft axis) between the inner and outer elements. This motion tends to slide or roll the O-ring, or sealing surface of the O-ring, back and forth with the reciprocal motion. Examples of a reciprocating seal would be a piston in a cylinder, a plunger entering a chamber, and a hydraulic actuator with the piston rod anchored.
Note: O-rings are generally not recommended for reciprocating installations in which the speed is less than one foot per minute. Consult a Parker Territory Sales Manager for more information on special seals to meet this requirement.
A standard application for an O-ring is sealing a tube fitting. There are industry standards for boss fittings, with a series of O-rings corresponding to each boss size. AS4395 is a fitting end that corresponds with AS5202 bosses. O-ring sizes are detailed in SAE J1926. O-rings used as boss seals can withstand much higher application pressures because the threaded hardware mates to eliminate a clearance gap.
It is sometimes necessary to add a retention feature to a face seal gland. The result is a dovetail and half-dovetail. This shape may also be called an undercut. It should be noted that although this method has been used successfully, it is not generally recommended. The inherent characteristics of the groove design limit the amount of void area. Normally acceptable tolerance extremes, wide service temperature ranges, and fluid media that cause high swell of the elastomer are conditions that cannot be tolerated in this type of groove design.
The cross section of the O-Ring can be measured in both the axial and radial direction. A face seal uses the axial cross section, or face of the O-ring to seal. When using an O-Ring as a face seal, a groove is cut in a flat surface, such as a plate. The O-Ring is placed in the groove and a second flat surface compresses the O-Ring. An O-Ring in a face seal design is static, meaning that that once installed, the O-Ring does not move. While the application pressure may cause the O-Ring to shift slightly, this is still considered a static seal. Face seals can seal internal pressure, external pressure, or both.
The cross section of the O-ring can be measured in both the axial and radial direction. A radial seal uses the radial cross section of the O-ring to seal around a piston. There are two variations of a radial seal: a male and a female design. The male design places the groove and O-ring on the piston. This may also be called a piston seal. A variation of this is the female design, which places the groove inside the bore. This may also be called a rod seal. Radial seals will see movement during installation, however once in place, the O-ring is considered static.