by Larry Thau, Victaulic

Unanticipated noise and vibration can be problematic for both occupants and processes within structures. Noise and vibration in piping systems can originate at pumps and other mechanical equipment. If the system design does not accommodate vibration, a variety of issues ranging from annoyances to actual business interruptions can occur.

Traditional Vibration Reduction

Designers have traditionally specified elastomeric flexible arch connectors to minimize noise and vibration where pumps connect to piping systems. These flex connectors create a discontinuity in the metal piping, which reduces the amount of vibration transmitted down the line. Commonly constructed of nylon, DacronÒ or polyester, these connectors are often spheroidal in shape to permit deflection in all directions. The disadvantage is in the weakness of the elastomeric arch: the lack of metallic containment and compression rather than pressure-responsive sealing.

The elastomeric flex connector's shape allows pressure to exert in all directions, but this often requires control units such as restraining rods, plates and/or anchors. These items are used to prevent excessive stretching of the unsupported elastomer due to system pressure thrusts. However, when such thrusts occur repeatedly and the connector is overextended through time, use and pressure, rupture or leakage can result. The connectors can be fairly expensive, and installation can be time consuming due to the complexity of the reinforcing systems. The compression sealing of the flanged construction often requires re-torquing to maintain a leak-tight joint.

Couplings' Sound and Vibration Reduction Qualities

Flexible couplings have proven as effective as flex connectors in handling deflection and reducing noise and vibration in commonly experienced frequency ranges. Couplings included in grooved mechanical piping systems provide additional performance benefits, making them a good option for pump connections, as well as joints throughout entire piping systems. These benefits include prevention of overstretching, and accommodation of deflection, expansion and contraction.

The elements of a grooved pipe joint

The elements of a grooved pipe joint

The mechanical joint, or coupling, is comprised of four elements: grooved pipe, a gasket, coupling housings, and nuts and bolts. The pipe groove is made by cold forming or machining a groove in the pipe end. A gasket enclosed in coupling housings is wrapped around the two pipe ends, and the key section of the coupling housing engages the groove in the pipe. The bolts and nuts are tightened with a socket wrench or impact wrench to hold the housings together. In the installed state, the coupling housings encase the gasket and engage the groove around the circumference of the pipe to create a leak-tight seal in a self-restrained pipe joint.

Like a flex connector, the coupling reduces vibration and noise transmission while handling deflection. The elastomeric gasket creates a discontinuity similar to that of a flex connector, while the design of a flexible coupling allows the joint to accommodate up to 5 deg of deflection.

3-D model of a pump with flexible couplings

3-D model of a pump with flexible couplings

The design of the coupling is different from a flex connector. The coupling's housings hold the gasket in compression to create a seal against the pipe, while providing both space for the elastomeric material to flex, and containment to prevent overstretching. Full metallic containment is provided. Couplings maintain noise and vibration attenuation qualities, as well as the ability to accommodate deflection, expansion and contraction, throughout the piping system's life.

The gasket material attenuates vibration as well as noise transference, and the ductile iron housings provide vibration-dampening qualities due to the materials' inherent dampening coefficient. In fact, testing conducted by SSA Acoustics in Seattle showed that three couplings placed in series in a pipe section dampened overall vibration amplitude by 80 to 90 percent, with each successive joint creating a further reduction in vibration.