An expansion joint can relieve stress in piping systems and prevent flange gaskets from being crushed. But which expansion joint is best for your specific application? Let us first describe the two types of expansion joints:
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Rubber &#; a flexible connector fabricated of natural and/or synthetic elastomers and fabric and, if necessary, internal metallic reinforcements designed to provide stress relief in piping systems due to thermal movements and mechanical vibration.
Metal &#; a flexible element (bellows) constructed of relatively thin gauge material (generally stainless steel) designed to absorb mechanical and thermal movements expected in service.
Typical Metal Expansion Joint
Temperature
Rubber joints with standard construction and materials have an upper range to 230°F. Most manufacturers, however, can offer special constructions up to 400°F. Metal expansion joints do offer a far greater range, from -420°F to +°F. However, working pressures are reduced at elevated temperatures.
Pressure
Rubber joints typically, depending on diameter, can have pressure capabilities up to 250-psi with a full vacuum rating. Metal joints can be designed for pressures up to -psi. The strength of metal is definitely an advantage in high pressure applications; however, the relative stiffness or spring rates coupled with thrust forces should be carefully examined. Piping systems/anchors must be designed to handle the combined load.
Typical Rubber Expansion Joint
Movements
Rubber and metal expansion joints have similar movement capabilities in the axial plane (compression and extension). However, rubber joints are certainly able to absorb far greater lateral movements when compared to metal joints that have similar face to face dimensions. Constructions (dual or universal) are available for metal joints where large movements in the lateral plane are required but these are considered special design and can be costly.
Spring Rates
Defined as the total force required to move an expansion joint 1&#; in any direction. Rubber and metal joints do have similar characteristics in the axial plane for the standard face to face dimensions. Metal joints are much stiffer when subjected to lateral motion and, therefore, typically have a much lower lateral movement capability. Note that all spring rate values are at 0-psig. Both rubber and metal joints produce thrust forces when pressurized that must be considered for proper system design.
Acoustical Impedance
Although well designed (multi-ply) metal joints can lower the transmission of visible vibration, they will continue to transmit distracting and/or damaging noise. Rubber joints significantly reduce the undesirable transmission in piping systems. The elastomeric composition of the joint acts as a dampener that absorbs the greatest percentage of perceptible noise and vibration.
Abrasion/Erosion Resistance
Metal joints typically have a wall thickness anywhere between .012&#; to .080&#;. Rubber joints on the other hand are much thicker, 0.5" to over 1". The thin gauge construction of metal joints makes them susceptible to erosive chemicals and abrasive liquids and slurries. Rubber joints are highly resistant to abrasion and erosion of all types and do outperform metal joints in the applications where these conditions prevail. Drop-in or fixed liners can be provided to enhance the life of metal joints in many of these applications but at best can only prolong the time to eventual failure.
Fatigue/Cycle Life
The fatigue life of a metal joint is affected by many factors such as temperature, pressure, movement, vibration and, of course, how the joint was initially designed. Typically, metal joints have a defined cycle or fatigue life that can be calculated through various formulas. Metal joints frequently succumb to fatigue failure from excessive cycling/movement. Rubber joints on the other hand are constructed of resilient elastomers and the joint itself acts as a vibration dampener, not susceptible to fatigue/cycle failure.
Installation/Maintenance
As a rule of thumb, rubber joints are 25% to 50% than metal joints. Rubber joints do not require additional gasketing and, in many cases, are installed easily by one or two men without the use of special handling equipment. Metal joints must be serviced occasionally to insure that the flange gasket is still intact and not deteriorated. For both rubber and metal expansion joints, control units are recommended to minimize possible damage to the expansion joint caused by excessive motion of the pipeline and in some applications, to absorb thrust forces. When control units are set to eliminate axial extension and compression, the only movement the joint can take is in the lateral plane.
Metal expansion joints are applied more frequently than rubber primarily because application conditions, e.g. temperatures and pressures, favor their use. Some experts in this industry estimate the metal expansion joint market to be 4X larger than the rubber expansion joint market. The writer of this article has been in the manufacturing business of both rubber and metal joints for over 35 years and would venture to say that is a good estimate.
It may appear that the above comparison is slanted toward the rubber expansion joints. The fact is, rubber can&#;t replace metal in all applications, but it is a better choice for many applications involving high vibration and sound dampening within the guidelines mentioned above. Consultation with a reputable manufacturer for your specific application is always recommended.
If you have questions about what joint is right for your application, please contact Gallagher's Engineering Department.
This article is a reprint of an article that appeared in Pumps & Systems in September of , and is included in the Fluid Sealing Association's Expansion Joints - Piping Technical Handbook.
Rubber flooring is a flooring type that has become quite popular in a wide range of settings. This type of flooring has already been used for sports flooring in gyms, fieldhouses, and weight rooms, and it is being used more in homes and commercial buildings. Not only are rubber floors resilient, durable, and easy to maintain, but they are also available in many different colors and designs to fit the decor of any space. Rubber floors have been commonly overlooked because they can be pricey and they have a reputation of being difficult to maintain. However, rubber flooring is actually quite easy to maintain and while it may cost more than some flooring options, its durability makes it a great long-term investment.
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The following are the main advantages of installing rubber flooring in your home or business.
Rubber floors can withstand a high volume of foot traffic and they are also water resistant, so they won&#;t be damaged by moisture or spills. The natural elasticity of rubber is what makes these floors so durable and resilient. They are great for absorbing impacts which is why they are popular in gyms and weight rooms. The ability to absorb impacts also makes rubber flooring an excellent option for commercial settings in which people are constantly on their feet. These floors provide more cushion than other flooring types which improves comfort and reduces injuries and fatigue.
The durability of rubber flooring comes from its density more than its thickness. The denser the rubber flooring is, the more resilient it is to tears and other damage. The following are the most durable types of rubber flooring:
Working out, lifting weights, and playing sports can be tough on the joints. Rubber flooring is excellent at absorbing impact during these activities which reduces the stress on joints like knees, hips, and backs. The ability to absorb heavy impacts lowers the risk of injuries.
Contrary to what many people believe, rubber flooring is relatively easy to maintain. All you need to do is vacuum the floor regularly because rubber floors accumulate dirt and debris, and mop the floor at least once per week using a mixture of water and a mild detergent. You should never use harsh chemicals for rubber floor cleaning because they will damage the rubber. Cleaning up spills quickly is also important for protecting rubber floors.
For more about rubber floor maintenance, check out Cleaning and Maintenance Tips for Rubber Flooring.
Rubber flooring has excellent slip resistance and typically far exceeds the minimum standard of the &#;coefficient of friction.&#; Rubber floors are commonly used as gym flooring for this reason and the high slip resistance also makes rubber floors an attractive option in healthcare facilities and nursing homes.
Unlike other flooring types, rubber flooring becomes more slip resistant as it gets wet. Water from spills, sweat, or condensation will not increase the risk of injuries. This also makes rubber flooring a great option for an outdoor workout space.
Rubber flooring is quite water resistant as it becomes more slip resistant when wet. When rubber flooring is finished with a floor finish and sealer, water will not be able to reach the subfloor.
Rubber is a natural raw material that comes from the sap of a rubber tree. The sap is extracted in a way that does not harm the growth of the tree and it is highly renewable. Rubber is also recyclable and it is regularly reused for a wide range of applications. Recycled rubber flooring is cut up into small pieces which can be used for mulch and playground surfaces, as well as to create entirely new products.
A major benefit of rubber flooring is that it is quick and easy to install. Flooring types like rubber floor tiles, rubber rolls, and rubber gym mats can be installed in a gym within a single day.
Rubber floor tiles can be installed simply by piecing the tiles together like a big puzzle and the tiles are heavy enough that no adhesive is required. Rubber flooring rolls can be installed simply by rolling them out.
While there are many advantages to using rubber flooring in a range of sports and commercial facilities, there are also some disadvantages that you should consider before getting new rubber flooring. The following are the main disadvantages of rubber floors:
Rubber floors have a distinct odor that comes from the rubber material and off-gassing from the glue that holds the floor together. Not all rubber flooring products have a strong smell as virgin rubber flooring is virtually odorless. The smell will depend on the raw materials and production process used for the flooring.
The odor is the strongest right after the installation, but the smell will become weaker within a few weeks. You can also eliminate the odor by mopping the floor with mild soap and water and keeping the area well ventilated.
Rubber flooring is not the most stylish option as they tend to be black, the natural color of rubber. However, there are rubber flooring options available with EPDM color flecks and virgin rubber flooring can be made in full colors. It is important to remember that colored rubber flooring is usually more expensive.
Rubber flooring tends to be an expensive option for gyms and weight rooms, but it is also extremely durable with features like shock absorbency and a non-slip surface that other flooring options do not have. Given the positive characteristics of rubber flooring, the investment may be worth it long term.
The advantages of rubber flooring make it a great option in a wide range of commercial and residential settings. Rubber floors have already been in use in gyms, fieldhouses, educational facilities, healthcare facilities, and other commercial settings and they are being used more in homes for laundry rooms, exercise rooms, and more. Kiefer USA is a leading provider and installer of Mondo rubber flooring and we have a wide range of Mondo products available for a variety of uses. Contact Kiefer USA by calling 800-322- for more information about our rubber flooring products for sports and commercial facilities.
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