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What Is a Flexible Coupling?

A person repairing a CV joint, which is a solid rotational flexible coupling.
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  • Written By: Paul Scott
  • Edited By: R. Halprin
  • Last Modified Date: 06 July 2014
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    Conjecture Corporation
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A flexible coupling is a mechanical device that allows an adjustable union to be formed between otherwise inflexible pipes or shafts. Flexible couplings permit transfer rotational motion between shafts and a continuous gas or fluid tight seal between pipes while allowing for a degree of axial misalignment. Solid shaft couplings typically consist of metal universal or U type hinges or machined metal half shells with flexible rubber inserts. These include couplings such as constant velocity (CV) joints and universal joints. Pipe couplings are generally molded rubber or stainless steel mesh sleeves which attach to the two pipes with standard jubilee type hose clamps.

Flexible couplings allow rigid shafts or pipes to be joined with a degree of deflection or axial misalignment while maintaining an uninterrupted transfer of torque or fluid flow. This functionality is particularly useful where shaft outputs change direction or pipes do not line up accurately. Examples include the change in drive shaft direction in rear wheel drive automobiles and the slight pipe misalignment common in automobile exhaust systems. Flexible coupling allows a rear wheel driven vehicle's drive shaft to dip down to the differential while maintaining full rotational speed and torque transfer. A stainless steel sleeve also allows two misaligned ends of an exhaust system to be joined with no carbon monoxide leaks or exhaust noise egress.

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Shaft couplings are generally rigid steel assemblies that allow for changes in drive direction courtesy of rotational or flexible elements in their design. Examples of rotational flexible coupling designs include the universal joint on the vehicles drive shaft and the double U type Cardan shaft joints used on machine drives. Other solid rotational flexible couplings include CV joints used to transfer drive torque from the half shafts to the front wheels on front wheel drive vehicles. Rigid/flexible combination joints consist of a pair of rigid steel elements which join two shafts via a flexible insert. These include joints such as the jaw coupling with its rubber insert and disc couplers which utilize a spring arrangement between two rigid discs.

Joining pipes with a flexible coupling allows the uninterrupted flow of fluids or gases where pipes are misaligned. These simple couplings are no more than rubber sleeves designed to fit snugly over the ends of both pipes and be locked firmly in place with hose clamps. These fittings may feature straight profiles where like pipe diameters are joined or stepped profiles to accommodate joints between dissimilar pipe diameters. Pipes carrying hot gases such as exhaust systems utilize heat resistant joints made of overlapping layers of stainless steel mesh and are attached to the pipes with U or hose clamps and exhaust sealant. As with all flexible coupling types, these joints allow continuity in the original purpose of the system while imparting flexibility to accommodate misalignment.

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