Universal tied, hinge, gimbal, in-line pressure balanced and elbow pressure-balanced are also possible. They all incorporate a restrained design, which manages pressure thrust forces in the piping system. The selection and application of these Rubber Expansion Joints categories are particularly useful in systems that have support structures or adjacent equipment with load limitations. All these styles can absorb set movements, reduce noise and vibration, have a long cycle life, compensate for planned misalignments and relieve pipe and anchor stresses.
Universal tied rubber expansion joints feature two resilient arch sections separated by a straight section to facilitate greater lateral-movement capability and a set of control or tie rods system. Control units are used as limit rods for secondary restraint in a properly anchored piping system, or as tie rods when the support structure or adjacent equipment have load limitations.
Hinge rubber expansion joints are designed to absorb angular movement in one plane only. The arrangement consists of a pair of hinge plates connected with pins and attached to the expansion joint’s hardware. The hinge assembly must be designed for the internal pressure thrust forces of the system. These Expansion Joints can be used in sets of two or three to absorb large lateral movements in a single plane.
Gimbal rubber expansion joints are designed to facilitate and isolate angular movement in all planes. The arrangement consists of two pairs of hinge plates connected with pins to a common gimbal ring and attached to the expansion joint’s hardware. The gimbal assembly must be designed for the internal pressure thrust forces of the system. They can be used in sets of two or sets of two with a single hinge design to absorb large lateral movements in multiple planes.
In-line pressure-balanced rubber expansion joints provide the only effective solution for directly absorbing large axial thermal movements (a specific design can also be provided to absorb some lateral movements) while continuously self-restraining the pressure thrust forces. This arrangement consists of tie devices interconnecting the main joint sections to the opposing balancing joint section and is commonly used when the support structure or adjacent equipment have load limitations.
Elbow pressure-balanced rubber expansion joints are designed to absorb all directional movement while continuously self-restraining the pressure thrust forces. This consists of tie devices interconnecting its main joint section to its opposing balancing joint section and is often used when the support structure or adjacent equipment have load limitations.
Unusual applications of rubber expansion joints may require the specification of: protective shields, protective cover or fire cover. These three types of covers, when manufactured of metal, have one end which is bolted to or clamped to the mating pipe flange. The other end is free, designed to handle the movements of the expansion joint.
Protective shields should be used on expansion joints in lines that carry high temperature or corrosive media. This shield will protect personnel or adjacent equipment in the event of leakage or splash. Wrap around protective shields of fluoroplastic impregnated fiberglass are the most common.
Internal liner consists of a sleeve extending through the bore of the expansion joint with a full-face flange on one end. Constructed of hard rubber, metal or fluoroplastic it reduces frictional wear of the expansion joint and provides smooth flow, reducing turbulence. This type sleeve should not be used where high viscosity fluids, such as tars, are being transmitted. These fluids may cause packing-up or caking of the arch area, which reduces movements and in turn may cause premature expansion joint failure.
Protective covers of expanded metal are used to prevent exterior damage to the expansion joint. Fire covers, designed oversize, are insulated on the I.D. to protect the expansion joint from rupture during a flash fire. They are normally installed on fire water lines.
Sun covers protect the elastomer against UV radiation. When possible, it is not recommended to insulate over elastomeric expansion joints.
Protection / Spray shield have some insulating properties. The containment of system temperatures can accelerate the aging of the product and makes required external inspections difficult.