Pump Expansion Joints
Construction
An elastomeric expansion joint consists of the tube, carcass and cover (see Figure 1). The tube is a leak-proof lining that protects the carcass from contact with the fluid medium. The tube material is selected to withstand the fluid’s temperature, chemical and abrasive characteristics. A full range of materials are available including chlorobutyl, nitrile, chloroprene, EPDM, chlorosulfonated polyethylene and fluoroelastomers, as well as PTFE.
Multiple plies of rubber-impregnated polyester or aramide tire cord are used in conjunction with steel reinforcement to achieve the necessary strength. The resilient arch is primarily designed to handle the required flexibility, but it also has to withstand the required temperature and pressure. The steel rings at the arch’s base are particularly important to prevent arch broadening from the continuous pressure. Arch broadening or migration can result in premature joint failure.
The cover, like the tube, acts to protect the carcass. The cover material is selected for its resistance to chemicals, oil, sunlight, acid fumes or ozone contamination, depending on the environmental conditions.
Control Rods
It is important to use control rods to protect the expansion joint when the piping system is not adequately anchored since pressure forces can quickly stretch the joint beyond its allowable limit and cause failure. This can be avoided with control rods set with clearances within the allowable movement limit of the joint.
Control rods cannot protect the expansion joint from thermal movements that exceed the design criteria of the expansion joint when the pipeline is fully anchored.
Conclusion
The primary functions of pump expansion joints include absorbing directional thermal movements, reducing noise, and vibration. They are also used to resist system shock, relieve pipe and anchor stresses, compensate for misalignment, and provide access to piping and equipment.
Single Wide Arch – Style 1101
Style 1101 single (1) wide arch rubber expansion joint (REJ) is designed to absorb large all-directional movements, reduce noise and vibration, have a cycle life in the tens of millions, compensate for misalignments, provide access to piping and equipment and relieve pipe and anchor stresses. Its spool type body is constructed with full rubber flanges, a high-grade leak-proof tube, multiple layers of high-strength tire cord, high tensile steel reinforcement, a seamless cover, and hot dip galvanized steel retaining rings. This construction, as a standalone expansion joint, represents the most cost-effective arrangement when used in rigid piping systems with main anchors (MA) and numerous guides at specific spac-ing. Control units can be externally or internally attached and used as limit rods for secondary restraint, or as tie rods when the support struc-ture or adjacent equipment have load limitations.
• Versatile hand-built construction, made in the USA
• Standard or custom face-to-face dimensions
• Available in custom offset arrangements and sizes not shown
• Wide flowing arch design
• Exceptional all directional movement capability
• Virtually eliminates sediment buildup
• Absorbs noise, vibration and shock
• Higher pressure rating than conventional expansion joints
• Hot dip galvanized retaining rings standard
• ANSI 125/150 lb. drilling standard, other standard drilling available, including ASA 300, DIN, PN, JIS, API, and Navy
• Excellent chemical and abrasion resistance
• Full vacuum rating (30″ Hg) in all sizes
• 250°F continuous service standard (400°F available)
• Compensates for minor misalignment and offset
• Low stiffness and deflection forces
• Integrally flanged design, no gaskets required
• High strength and simple to install
• Provides easy access to piping and equipment
• Filled arch design available (reduces movement by 50% & increases spring rates by 400%)
• Wide variety of tube and cover elastomers available, including Pure Gum Rubber, Neoprene, Butyl, Nitrile, EPDM, Viton®, Teflon®, Food Grade, and more
PUMP EXPANSION JOINT STYLE 1101
PUMP EXPANSION JOINT STYLE DN900
Assessing alternative pump piping solutions
Some industry professionals have voiced their concerns relating to the use of rubber expansion joints in pump piping applications. One recent claim cited installation misalignment and the expansion joint’s stiffness or spring rate as the reason for increased vibration levels across the system and more force being applied on the pump. While every pumping system is different, it is much more likely that the pressure thrust force from an un-restrained expansion joint would impose far more force and adversely affect pump performance, as opposed to a few hundred pounds of spring rate load. An important point that is commonly missed is that unless the rods of the control unit are snug tight (tied) the expansion joint could impose a potentially damaging pressure thrust force on the pump. Nevertheless, some feel the solution is to eliminate expansion joints, increase the rigidity of the piping system, and tighten installation tolerances; which is an impractical and problematic approach.
Contact Us
Contact us for more information or for help with your specific application.