Rubber Expansion Joints

Rubber expansion joints have been at our core since the beginning. From a simple flanged, single open-arch type expansion joint with rubber tube and cover and fabric and metal reinforcing to much more demanding and exotic styles. Our rubber liners and covers can be constructed of virtually any type of synthetic or natural elastomer, including Viton. PTFE liners are also an option. For greater movement capabilities, we can build expansion joints with double, triple, or even quadruple arches. For applications involving sediments or high-velocity media, filled-arch styles are available. To accommodate changes in pipe sizes, we offer either concentric or eccentric reducing style joints. For basic flexible connections and noise reduction at pumps, consider our spherical expansion joints with rotating steel flanges. Necessary accessories for most rubber expansion joint applications include retaining rings and control units. Safety shields are also an option.

Why choose a rubber expansion joint?

Rubber expansion joints and connectors are the ideal choice for many piping situations, and they have several uses.

1. Rubber expansion joints are most often used as a flexible connector between a vibrating piece of mechanical equipment and the pipeline. These rubber connectors are generally the best solution for isolating noise and vibration and to keep these unwanted dynamics from being transmitted down the pipeline to occupied areas. Single and double spheres are quite common for this application in conveying water in HVAC systems.
2. They can also be used to absorb pipe movements. Spherical connectors are available in either single sphere and double sphere to absorb greater pipe motions. Spool type expansion joints can be built with multiple arches to take up greater movements.
3. Rubber connectors will also provide for a reasonable amount of pipe offset caused by equipment settling.

Flex Connector vs. Expansion Joint

A rubber expansion joint can be used as a flex connector, to absorb noise and vibration from adjacent equipment. In this application, there are usually not anchors in the piping systems and the rubber expansion joint should employ control units to keep the product from expanding under pressure. Control unit nuts should be snug (using 1/4″ thick rubber washers. Alternately, these connectors can be used as a piping expansion joint to absorb thermal pipe growth or temporary pipe movements. Like metal bellows expansion joint systems, in these cases, this rubber product becomes part of the expansion joint system which includes main anchors and pipe alignment guides. Rubber expansion joints can also be used as both flex connectors and expansion joints in the same system. When using rubber connectors as an expansion joint in the piping system, they may or may not be located next to vibrating equipment. Control units can be used as a back-up safety device in the case of an main anchor failure, but nuts and washers should be loosened to allow for the full extension or contraction of the expansion joint.

(Above) Rubber connector used as an expansion joint to take up thermal growth and other pipe movements. There are anchors located on either side of the expansion joint, the joint is located as close to an anchor as possible, and pipe alignment guides are spaced out on the piping to prevent pipe bucking under column loads.

(Above) Rubber connectors used as flex connectors for noise and vibration. There are no piping anchors present and control units are installed on the rubber connectors.

Anchor Load Considerations

Introducing a flexible product like an expansion joint to your piping system adds an aspect that must be taken into consideration when designing the piping system. Due to pressure thrust forces and spring loads, main anchors must be engineered to handle these increased loads. Unless restrained by control rods, expansion joints expand under pressure, creating pressure thrust forces on the anchors. In addition, the inherent stiffness of the expansion jointy must be overcome in order for these products to absorb thermal pipe growth. For each size and type of expansion joint, we can calculate the effective area of the joint. This figure is multiplied by the system pressure to determine the pressure thrust force. Each product and size also has a spring rate–the force required to compress, expand or offset the product by 1-inch. If we are expecting, for instance, 2-inches of pipe growth and the compression spring rate of our rubber expansion joint is 1000 lbs. per inch, our spring force is calculated to be 2000 lbs. This figure will be added to the pressure thrust force to determine the combined force on system anchors. If there are pipe alignment guides involved, we will also have some frictional forces of the pipe passing through the guides. More information on expansion joint systems can be found in our Metal Expansion Joint section of our website.

Anchor Load = Pressure Thrust Load + Spring Load + Frictional Loads

Configurations

There are many choices of styles and configurations of rubber expansion joints. Rubber spheres are mainly used as flex connectors and connected to HVAC equipment to absorb noise and vibration. This type of connector is available in single sphere and double sphere flanged connectors, and double sphere threaded connectors. Flanges are made of plated steel and are able to rotate for easy alignment. Generally, these connectors are made of EPDM or Neoprene rubber. Spool or arch type rubber expansion joints are generally built for more specified applications. They are at least partially hand-built, with wrapped rubber covers, duck and rubber flanges, and a sharp arch configuration to absorb pipe movements. Consider these configuration choices:

• Narrow or wide arch style

• Multiple arches for greater movement capabilities

• Filled arch types (with rubber foam) so that arches do not fill with media

• Reducing styles – concentric or eccentric

• Flange options – standard or custom drilling or no drilling (drilling one side only is sometimes a good option)

• Face-to-face dimension choices

• Imprinting of serial number for traceability

Elastomer Choices, Pressure Ratings, Sizes

Choice of elastomer is very important when your pipeline is conveying liquids other than water. Various elastomers, fluoroelastomers, and fluoroplastics have differing compatibility to chemicals and abrasive slurries. For instance, expansion joint liners can be formulated to handle raw sewage, acids, alkaline, hot air, pure drinking water, abrasive slurry, and many other chemicals and media. Tube liners of natural or pure gum rubber are ideal for use with abrasive material. Synthetic Nitrile rubber is best for raw sewage, EPDM is a good choice for many hot air applications. For chemical applications, your best choice may be Viton, PTFE, or Hypalon. Unisource does not recommend rubber expansion joints for use with compressed gases, steam, or extreme temperature liquids. For shipboard service for commercial vessels, we offer rubber expansion joints that meet the requirements of the U.S. Coast Guard and the Code of Federal Regulations. Our U.S. Navy mil-spec joints can be built with ANSI flange drilling or Navy drilling.

Also, look carefully at the maximum pressure that your piping system will see, It may be during the system hydro-test. Standard rubber expansion joints are made in working pressures of 150 to 225 PSI in most sizes. High pressure products can be manufactured upon request. Keep in mind that higher pressure expansion joints will be heavier and more stiff than lower pressure joints. Generally, rubber expansion joints are reinforce with polyester fabric plies along with steel hoops for vacuum rating. For higher-pressure ratings, Kevlar reinforcing might be indicated.

Rubber expansion joints are readily available in sizes from 1-1/2 inch to 36 inch. Single and double rubber spheres are made in hydraulic molds and range in size from 1-1/2 inch to 16 inch, with larger sizes to 20″ available upon special order. Spool-type or arch-type expansion joints can be made in much larger sizes. Sizes on these products vary from 1-1-/2″ to 102″ diameter.

Series 301 Ultra-Sphere Single Sphere

Precision molded Ultra-Sphere connectors will perform double duty as a vibration elimination pump connector, or as an expansion joint, absorbing pipe movements.

Ultra-Sphere connectors are perfect for HVAC or industrial applications where a flexible connector is needed to absorb axial, transverse, or angular pipe movements. Ultra-Sphere rubber connectors are also superior to braided metal connectors for absorbing vibration and noise generated by mechanical equipment.

Ultra-Sphere connectors are precision molded in hydraulic presses. The spherical design ensures that internal pressures are exerted in all directions, distributing the forces evenly over a large area. The spherical design acts as a free-flowing arch, reducing turbulence and growth due to pressure thrust forces.

These connectors are manufactured with a high-quality EPDM rubber tube and cover, and nylon tire cord reinforcing. Special elastomers such as Neoprene, Nitrile, Hypalon, and Butyl are also available. The standard EPDM material is superior to competitive connectors made of Neoprene due to their higher temperature resistance and physical properties. Galvanized steel floating flanges are recessed to engage the rubber beaded end of the expansion joint and rotate easily for speed of installation.

Style 301 single sphere connectors are ideal for absorbing small stress motions and absorbing the noise and vibration emitted by mechanical equipment. The face-to-face dimensions of these single sphere connectors match the corresponding dimensions of spool type expansion joints, facilitating direct replacements. This short face-to-face dimension translates to economy of space in the piping system and ease of handling and installation.

Ultra-Sphere Series 301 connectors are manufactured to meet or exceed the pressure, movement, and dimensional ratings of the Rubber Expansion Joint Division, Fluid Sealing Association.

Sealing Information: When installing rubber expansion joints, it is the responsibility of the installer to ensure bolting forces are evenly distributed to provide optimum clamping force to prevent the connection from leaking. When the expansion joint is being installed in non-ferrous piping systems, such as PVC, reinforcement of the mating flanges may be required to increase the mating flange rigidity.

Unisource recommends the use of ring gaskets or full face gaskets when a rubber expansion joint is being installed against a raised face flange. The use of ring gaskets or full face gaskets may be required when installing PTFE lined expansion joints. If you should have any questions pertaining to the installation, please call Unisource or refer to the Fluid Sealing Association Technical Handbook for Non-Metallic Expansion Joints.

Series 302 Ultra-Sphere Double-Sphere

Series 302 double sphere connectors are similar in construction to the single sphere style, but with a second sphere to provide even more pipe movement absorbing capability and even greater efficiency for noise and vibration control. In fact, Series 302 connectors offer the industry’s best option for vibration reduction—up to 98%, depending on pressure and frequency. A plated steel external root ring surrounds the connector between the spheres, preventing ballooning or swelling under pressure

Ultra-Sphere connectors are precision molded in hydraulic presses. The spherical design ensures that internal pressures are exerted in all directions, distributing the forces evenly over a large area. The spherical design acts as a free-flowing arch, reducing turbulence and growth due to pressure thrust forces.

These connectors are manufactured with a high-quality EPDM rubber tube and cover, and nylon tire cord reinforcing. Special elastomers such as Neoprene, Nitrile, Hypalon, and Butyl are also available. The standard EPDM material is superior to competitive connectors made of Neoprene due to their higher temperature resistance and physical properties. Galvanized steel floating flanges are recessed to engage the rubber beaded end of the expansion joint and rotate easily for speed of installation.

Series 303 Ultra-Sphere Union Connector

Unisource Series 303 female union connectors are ideal for isolating small diameter piping from vibrating mechanical equipment.

In smaller size applications where threaded connectors are normally used, Series 303 double sphere union connectors will accommodate both pipe motions and vibration. Series 303 connectors will provide over 1” of axial compensation, as well as impressive ratings for lateral and angular deflection. The Neoprene or EPDM rubber body construction is also far superior to metallic connectors for eliminating noise and vibration generated by equipment such as pumps, chillers, and air handlers. These connectors are extremely versatile and can be used in a variety of services, and are available in designs to handle up to 150 PSIG and temperatures up to 200 degrees F.

Ultra-Sphere expansion joints are precision molded in hydraulic presses. The spherical design ensures that internal pressures are exerted in all directions, distributing the forces evenly over a large area. The spherical design acts as a free-flowing arch, reducing turbulence and growth due to pressure thrust forces.

Series 303 Ultra-Sphere connectors are constructed with a high-quality EPDM tube and cover and nylon tire cord reinforcing. Neoprene construction without cables is also available.

Series 303 EPDM connectors offer high-temperature EPDM rubber for tube and cover construction. Galvanized ductile iron threaded female union ends are standard. Special cable restraint attachments surround each end to prevent the connector from over-extending due to pressure thrust. A steel body ring encircles the rubber between the spheres to provide stability under pressure.

Series 1200 Flexi-Spool Expansion Joints

Style 1200 “Flexi-Spool” rubber expansion joints are designed to handle a multitude of industrial applications. “Flexi-Spool” expansion joints are a spool-type, hand-wrapped expansion joint with several construction features that provide advantages over standard expansion joints. The wide-arch style of “Flexi-Spool” provides several times the movement capability of standard narrow arch style joints. A high-pressure reinforcing combines both polyester fabric plies with steel wire for impressive working pressure and vacuum ratings, even at extended temperatures. A thick, wrapped-on rubber cover protects the reinforcing from damage and the environment. The arch can be filled with a rubber foam if needed (designate style FA) to accommodate media that might clog or degrade an open arch. Full-face duck and rubber flanges provide an optimum sealing surface. Both tube and cover can be provided in a variety of materials in order to handle conditions involving chemicals, moderate temperature extremes, abrasion, or other conditions. Materials include Neoprene, Chlorobutyl, natural rubber, Nitrile, Hypalon, and are also available with white PTFE liners. Series 1200 Flexi-Spool expansion joints can also be manufactured in reducing styles–both concentric (style RC) and eccentric (style RE). Also, to accommodate greater pipe movements and to reduce spring rates, multiple arch styles can be built. Two or three arch expansion joints are common. Spool type expansion joints are designed to be used with metallic retaining rings, and metallic control units when required.

Series 1500 Ultra-Spool Expansion Joints

Series 1500 Ultra-Spool expansion joints are a hand-built product for the most demanding of applications. A precision built product designed to provide exacting specifications for tube and cover requirements, pressure ratings, markings, and special options. The wide arch will provide much greater movement capabilities than standard narrow arch designs. The tube can be constructed using a variety of elastomer products including EPDM, Chlorobutyl, Neoprene, Nitrile, Hypalon, Viton. When needed, a white PTFE liner can be added. Rubber tube thicknesses are approximately 1/4” thick for greater wear life. The arch can be filled with a rubber foam if needed (designate style FA) to accommodate media that might clog or degrade an open arch. Reinforcing of multiple plies of polyester provide 225 PSIG working pressure in sizes up to 14” diameter. Thick steel body rings add hoop strength and assure high vacuum rating, even at extended temperatures. Each expansion joint has a permanently embossed brand on the cover with information including individual serial number for identification. Series 1500 Ultra-Spool expansion joints can also be manufactured in reducing styles–both concentric (style RC) and eccentric (style RE). Also, to accommodate greater pipe movements and to reduce spring rates, multiple arch styles can be built. Two or three arch expansion joints are common. Spool type expansion joints are designed to be used with metallic retaining rings, and metallic control units when required.

Retaining Rings

Unisource metallic retaining rings are designed for use on all elastomeric expansion joints with duck and rubber flanges. Metallic retaining rings must be used when connecting the rubber flanges of expansion joints to the mating piping system flanges. Retaining rings consist of split circular sections of 3/8” thick carbon steel or stainless steel, drilled to match the expansion joint flanges. Edges are chamfered. Standard retaining rings are zinc plated or galvanized, but can be specially ordered in stainless steel or epoxy coated. Sizes range from 1-1/2” to 144”. Constructed to meet FSA Rubber Expansion Joint Division standards.

Control Units

Unisource recommends the use of control units on rubber expansion joints when piping anchors are not present and to act as a back-up safety device in the event of anchor failure.

Control units are recommended for use on both sphere and spool type rubber expansion joints when it is not possible to install solid anchors in the piping system. Although it is theoretically possible to pre-elongate spherical connectors to avoid the effects of extension due to pressure thrust forces, Unisource does not recommend this practice in lieu of anchors and control units due to the unpredictability of subsequent pressure spikes and system pressure tests. To isolate vibration that could travel across solid control rods, Unisource utilizes minimum 1/4” thick reinforced grommets on each end of our control unit rods.

A standard control unit set consists of two threaded rods, four triangular plates, eight steel nuts, four flat washers, and four 1/4” thick rubber grommets. Always consult the system engineer to determine the highest pressures that the system will see to determine the number of rods needed. Unisource control units are based on Fluid Sealing Association standards and are rated to equal or exceed the following specifications:

Series ED, Style U, Rubber U-Joint For Duct Systems

UNISOURCE SERIES ED, Style U expansion joints are elastomeric in both body and flange and are available in Neoprene, Hypalon, EPDM, Butyl, or fluoroelastomer Viton. Thinner in overall gauge than pressure piping expansion joints to protect thin wall duct systems. Standard circular expansion joints have integral duck and rubber flanges, drilled to order. Rectangular style also incorporates rubber flanges, utilizing square corners and special drilling. “Continuous corners” eliminate splices through the body of the expansion joint near the corners. The inherent flexibility of rubber provides long service life even in applications of high vibration or flutter. Style “U”, a U-joint without arch, designed for normal ducting movements. Series ED expansion joints require metallic backing rings or bars. Typical retaining bars are made of 3/8” x 2” wide A-36 chamfered or round edge bar stock.

Series ED, Style A, Rubber Expansion Joint For Duct Systems

UNISOURCE SERIES ED, Style A expansion joints are elastomeric in both body and flange and are available in Neoprene, Hypalon, EPDM, Butyl, or fluoroelastomer Viton. Thinner in overall gauge than pressure piping expansion joints to protect thin wall duct systems. Standard circular expansion joints have integral duck and rubber flanges, drilled to order. Rectangular style also incorporates rubber flanges, utilizing square corners and special drilling. “Continuous corners” eliminate splices through the body of the expansion joint near the corners. The inherent flexibility of rubber provides long service life even in applications of high vibration or flutter. Style “A”, a rounded arch type joint, is designed for increased axial movement capabilities without pre-extension or compression. Series ED expansion joints require metallic backing rings or bars. Typical retaining bars are made of 3/8” x 2” wide A-36 chamfered or round edge bar stock.

Series ED, Style HA, Rubber Expansion Joints For Duct Systems

UNISOURCE SERIES ED, Style HA expansion joints are elastomeric in both body and flange and are available in Neoprene, Hypalon, EPDM, Butyl, or fluoroelastomer Viton. Thinner in overall gauge than pressure piping expansion joints to protect thin wall duct systems. Standard circular expansion joints have integral duck and rubber flanges, drilled to order. Rectangular style also incorporates rubber flanges, utilizing square corners and special drilling. “Continuous corners” eliminate splices through the body of the expansion joint near the corners. The inherent flexibility of rubber provides long service life even in applications of high vibration or flutter. Style “HA”, a sharp arch type joint, is designed for increased axial movement capabilities without pre-extension or compression. Series ED expansion joints require metallic backing rings or bars. Typical retaining bars are made of 3/8” x 2” wide A-36 chamfered or round edge bar stock.