S-Flex (Sleeve) Couplings: How To Select a Coupling

While the Lovejoy S-Flex PDF catalog provides the necessary information and data to properly size an S-Flex sleeve coupling, a few things to keep in mind that you will need to know are: 

• Horsepower (HP or KW) and speed (RPM) of the driver and/or torque
• Shaft and keyway sizes of driver and driven equipment
• Application description
• Environmental conditions (such as temperature, corrosive chemicals, space limitations) as well as misalignment expected

Lovejoy's published torque ratings are maximum nominal values, and care must be taken to insure that proper service factors are applied for the application to come up with a design torque. 

This calculated design torque must still be less than the published nominal torque rating. Service factors allow for adequate coupling life given that different types of equipment, even if the torque requirements are the same, will put different stresses and wear on a coupling.

Other critical characteristics to be sure to check before making a final coupling selection include:

• Maximum bore capacity of the flanges (as well as minimum bore in some cases)
• Maximum speed capability of the coupling size
• Resistance of the sleeve to the environmental conditions expected
• Size of the coupling (O.D. and OAL) fits into the "envelope" available

Lovejoy's catalogs also give charts with the specific UPC # (Universal Product Code) for each component of a complete coupling. For help with quickly determining design torque and selecting the proper S-Flex coupling size, consider downloading the Lovejoy iPhone & Android selection app or use a similar tool on your desktop. 

To keep learning about S-Flex couplings on this blog, go to:

S-Flex (Sleeve) Couplings: Product Overview

S-Flex (Sleeve) Couplings: Flange Types

S-Flex (Sleeve) Couplings: Elastomer (Sleeve) Types

S-Flex (Sleeve) Couplings: Failure Analysis

S-Flex (Sleeve) Couplings: Elastomer (Sleeve) Types

S-Flex elastomeric sleeve type flexible couplings come in three different standard material types, as well as single piece, split single piece, and split two piece designs.

Materials

EPDM - This is the standard material, a rubber-like compound which has the highest temperature rating (275°F/135°C) of the sleeves available. It provides good resistance to most commonly found chemicals and is not affected by dirt or moisture. This sleeve is a dull black color, can handle 1° of angular misalignment, .010" (size 3) to .062" (size 16) parallel misalignment, up to .124 inches axial misalignment, and up to 15° torsional wind-up.

NEOPRENE - This material has better chemical resistance than EPDM, especially to oil, but is rated only for a max. temperature of 200°F (93°C). The color of the sleeve is black with a shiny finish and a green dot for easy identification. The Neoprene and EPDM sleeves have the same torque rating, misalignment ratings, and wind-up rating.

HYTREL - This is a polyester elastomer designed for high torque and excellent chemical resistance. It carries four times the torque of the EPDM/Neoprene materials but is limited to ¼ ° angular misalignment and parallel from .010" (size 6) up to .035" for size 14 couplings. The Hytrel material is orange in color, with torsional wind-up up to 7°. When using this coupling, care should be taken to ensure the coupling is not over-sized and some wind-up occurs (otherwise tooth chatter could lead to premature elastomer wear and failure).  

 

Sleeve Designs 

 
One-piece solid - The one piece solid sleeve design is noted as the JE (EPDM), JN (Neoprene), and H (Hytrel) types, and is generally the least expensive of the rubber sleeves. It is available in sizes 3-10 for JE, 3-8 for JN, and 6-12 for H.

One-piece w/split - The one-piece split design is noted as the JES (EPDM) and JNS (Neoprene) types. This design is used for applications where the shafts are positioned closely together and the sleeve must be "peeled away" for replacement. The design is stocked by Lovejoy in sizes 3-9 for JES, and 3-8 for JNS.

Two-piece split - The two-piece split style sleeve is made up of two completely separated halves. For the E (EPDM) and N (Neoprene) styles, a retaining ring is used to prevent the sleeve from extruding outward under speed. The H (Hytrel) is such a rigid material that the ring is not necessary. The E sleeve is available for size 5-16 couplings, the N sleeve for 5-14, HS for 6-14. This design is popular given its ease of installation and replacement.

 

 

Bulk Packs

For high usage customers, the JE, JES, and E sleeves are available in the most popular sizes in bulk packs of 5 or 10 pieces. 

To get technical information on S-Flex couplings, please visit Lovejoy's S-Flex product page, or download the PDF catalog. Additionally, installation instructions and installation videos can be accessed here. 

To keep learning more about S-Flex couplings on this blog, please see:

S-Flex (Sleeve) Couplings: Product Overview

S-Flex (Sleeve) Couplings: Flange Types

S-Flex (Sleeve) Couplings: How To Select a Coupling

S-Flex (Sleeve) Couplings: Failure Analysis

S-Flex (Sleeve) Couplings: Flange Types

The S-Flex (sleeve) coupling has 5 primary flange types, each with their own benefits. 

J Type

J Type 

The first four sizes of flanges (size 3J to 6J) are available in this type which differs from the S Type in that the J Type does not have as great a length-thru-bore. This is due to the absence of a projection in the cast material on the J-type flange at the inner face. Thus, where both J and S flanges are available (sizes 5 and 6 couplings), the S flange has a greater maximum bore capacity than the J.  

This flange is very economical and provides a coupling which is only slightly more expensive than a comparable jaw coupling. Due to the high torque of the Hytrel sleeves, the J-type flanges can only be used with EPDM or Neoprene sleeves.

S Type (with E Sleeve)

S Type 

The S Type covers the 11 coupling sizes from 5S through 16S. These flanges all have the projection at the inner face of the casting which provides for greater shaft engagement. The S-type flanges can be used with any of the sleeve materials.
 

B Type 

The B Type flange is modified to accept the industry-standard QD bushing, and is offered in sizes 6B through 16B. The use of bushings limits the bore capacity of the coupling, but provides a very firm grip on the shaft and can simplify the stock room of many customers (if they use bushings on other power transmission components). Due to the torque limits of the QD bushing, B Type flanges cannot be used with Hytrel sleeves. 


T Type 

Similar to the B Type for QD bushings, the T Type is a standard flange modified to accept the style of bushing called Taper-Lock.  There are two ways to mount the bushing to the flange, from the serration side (Rear) or from the same side of the flange as the shaft is inserted initially (Front). We call these versions the TR for Taper-Lock/Rear and the TF for Taper-Lock/Front. Be sure to determine if the bushing being used has either UNC threads (which have a 60° thread angle) or B.S.W. (55° thread). As with the B Flanges, the T Type cannot be used with Hytrel sleeves due to the limits of the Taper-Lock bushing ratings.
 

SC Type Coupling

SC Type

These meet standard API (American Petroleum Institute) spacing requirements for pump disassembly. One of the other benefits to the S-Flex spacer couplings is that the various components can be mixed/matched in combinations to achieve dozens of other shaft separations beyond the API standards of 3 1/2", 5", and 7". 

SC Type Flange

The SC Type spacer coupling is achieved by using a Spacer Flange (with nomenclature such as 8SC35 or 8SC44) to which is bolted a Spacer Hub (8SCH for example). There are usually three lengths of Spacer Flanges available in each size coupling. The Spacer Hub has the finished bore and keyway for the driver/driven shaft. Each half of the full spacer coupling uses a Spacer Flange/Hub combination. Half-spacer couplings are possible, as well as combining different lengths of Spacer Flanges.

SC Type Hub

S-Flex spacer couplings are available from size 5 through size 14 couplings. Any of the sleeve materials can be used with the SC Type coupling. The Spacer Hub is bolted to the Spacer Flange with four hex head cap screws. By removing these screws, the center section of the coupling can be dropped out.

To get technical specifications fo S-Flex couplings, please visit Lovejoy's website product page or download the S-Flex pdf catalog. Detailed installation instructions and videos for these products can also be found here. 


To keep learning about S-Flex couplings on this blog, go to:

S-Flex (Sleeve) Couplings: Product Overview

S-Flex (Sleeve) Couplings: Elastomer (Sleeve) Types

S-Flex (Sleeve) Couplings: How To Select a Coupling

S-Flex (Sleeve) Couplings: Failure Analysis

S-Flex (Sleeve) Couplings: Product Overview

The S-Flex (Sleeve) coupling is a coupling type that Lovejoy has been selling since 1985, and one that has very strong acceptance in the US pump industry. While this coupling has gained acceptance in other applications and in other parts of the world, the US pump industry (and especially the ANSI chemical process pump segment) remain its strongest core market.

Much like Lovejoy's signature jaw coupling (Lovejoy was the patent holder for the straight jaw coupling), the S-Flex is simple three part design.  A standard coupling is comprised of 2 flanges and 1 sleeve.  Unlike a standard jaw coupling, the sleeve of an S-Flex coupling is in-shear between the two flanges, with teeth around its perimeter which mate to corresponding teeth in the flanges (much like a gear coupling). The torque is transmitted through the twisting of the elastomeric sleeve. There are several features to this coupling which translate into tangible benefits to the user:

• As with other elastomeric couplings, it is maintenance-free and non-lubricated.
• Since the design is double-engagement, it is very soft radially. It provides very low reactionary loads when misaligned which protects bearings/shafts.
• The torsionally soft design of an in-shear elastomer helps to damp out most peak overloads and prevent vibratory torque from going back to the driver. The EPDM and Neoprene sleeves will twist as much as 15° at full torque, Hytrel up to 7°.
• The sleeve has a large open center which allows close positioning of the shafts.
• The in-shear design allows the coupling to act as a "fuse" to protect the driver and driven from torque spikes or system overloads which might cause more expensive damage than just a replacement sleeve. The torque overload capacity of this coupling is only 3 or 4 times the rated torque (the point at which the sleeve will tear, round-off the teeth, or "pop out"), versus the 6 or 7 times for a jaw coupling.

The S-Flex style of coupling is best suited in the following applications:

• Where coupling alignment may be hard to maintain over a period of time. The S-Flex is a somewhat forgiving coupling and will not load the bearings due to misalignment. The sleeves won't last as long but the coupling doesn't harm the equipment.
• Non-piloted pump applications, where the motor and pump are on a base plate but there is no pump mounting bracket involved.
• Closely coupled shafts.
• For shafts that are relatively small for the torque loads or the bearings are light duty.

Care should be taken however, that S-Flex is not used under the following conditions:

• High-inertial loads, especially if they produce variable torque loads.
• Where overloads/spikes are expected to be greater than 2x nominal ratings.
• Any reciprocating engine driven equipment. S-Flex does not respond well to torsional vibrations. This applies to reciprocating pumps and compressors as well.
• Do not select this coupling if it is used at anything less than 25% of its rated torque. The sleeve teeth will wear prematurely due to the rubbing action against the flange if too lightly loaded. This can be a concern particularly with the Hytrel sleeves since they have such high ratings.

In general, the S-Flex coupling will work well on electric motor driven applications with uniform loads such as; centrifugal pumps, blowers and fans, screw compressors, some conveyors, line shafts, and vacuum pumps. It competes primarily with other elastomeric designs such as tire types, jaw couplings, as well as Grid spring couplings for some pump applications.

The major manufacturers of this design all produce their product to be broadly dimensionally interchangeable. However, since the design has quite a few "mating" points with the sleeve/flange teeth, the possibility of imperfect fits from one manufacturer to another is always possible. This is due to the tolerance that is built into each company's initial design criterion (i.e. how tight or loose they want the fit between components to be), and the state of wear of the tooling that produces the sleeves and flanges. Furthermore, rubber quality/performance does vary between manufacturers. As such, Lovejoy recommends that mixing of components from different manufacturers be avoided if at all possible. This also assures that the product warranty is not voided.

To keep learning on the blog, go to:

S-Flex (Sleeve) Couplings: Flange Types

S-Flex (Sleeve) Couplings: Elastomer (Sleeve) Types

S-Flex (Sleeve) Couplings: How To Select a Coupling

S-Flex (Sleeve) Couplings: Failure Analysis

To get Lovejoy S-Flex technical data, part numbers, or download a product catalog, please visit Lovejoy's product page, where you can download catalogs, search for part numbers, and click through to watch installation videos. 

Flexible Coupling Basics - A Quick Primer

Speaking from 30,000 feet, power transmission couplings are devices used to connect two shafts together, transmitting system torque from one shaft to the other. (When one shaft spins, the coupling's job is to make the other shaft spin.) Within the huge array of coupling solutions, couplings can be broadly broken down into two primary types: rigid (which we will briefly touch on) and flexible (which we will then dive into). 


Rigid couplings (an example pictured left) are exactly that... rigid. They firmly connect the two shafts together without any additional features or capability of accommodating/handling system misalignment. Rigid couplings are generally simple and cost-effective for applications where misalignment is not a concern.

In contrast to rigid couplings, flexible couplings (the focus of this article) have an integrated flexing element or design component that allows for some degree of misalignment handling & management. Within the vast flexible coupling world, couplings can further be broken into two major sub-groups: elastomeric couplings and metallic couplings.

Elastomeric (flexible) couplings - Elastomeric couplings are couplings that include a flexing rubber or plastic element to both accommodate misalignment and dampen system vibrations. Within the elastomeric coupling subset, there are many style and designs. This post will focus in on and provide a quick cliff notes overview of the 3 major elastomeric flexible coupling product types: compression loaded, shear loaded, and torsional.

(Note: Lovejoy's "The Coupling Handbook" takes a much deeper dive into everything this blog post covers, and the Mechanical Power Transmission Association also has an excellent 7 page PDF document, title Elastomeric Coupling Primer, that would make for great follow-on reading as well.)  

Compression Loaded: Let's start the elastomeric compression loaded discussion with the bread and butter all-purpose industrial coupling: Lovejoy's very own straight jaw coupling. This coupling comprises two hubs with straight jaws that are interlocked with an elastomeric spider (we call it a spider because, yes, it looks like one) in between the two hubs (with the spider serving as the flexing element) transmitting torque in compression. One feature of this coupling is that it is considered "fail-safe". If/when the spider eventually wears out (which, after a full service life it will, as any/every rubber based product will eventually break down), the metallic jaw hubs can then continue to carry the load (though not as smooth, and with a bit more noise). (Note: It is certainly preferable to replace a spider before it fails, generally when it has been compressed to 75% its original size... as this is much cheaper and quicker than replacing both hubs and the spider, which will be required if the hubs start to wear on each other if the coupling is run in the absence of a functional spider.)

The basic jaw coupling (known as an L-line, and pictured above next to "Compression Loaded" title), has many variations for specific applications. These include aluminum (lightweight) and stainless steel (for food and pharmaceutical applications) hubs, special spiders made for high temperatures, high torques, chemical and oil resistance (and even a bronze spider for high torque, low speed applications), quick change out radial spiders, drop out spacers, and a variation (known as a jaw in-shear & pictured left) that turns a "fail safe" jaw coupling (where the elastomer is in compression) into a "non-fail safe" coupling (where the elastomer is a combination of both in-shear and in compression, preferable for applications where torque transmission should cease should the coupling not be operating at full capacity).

In Europe, a curved jaw coupling variation has become the standard industrial coupling, and Lovejoy sells a large number of curved jaw couplings into Europe through Lovejoy's German affiliate. Lovejoy also replaces a significant number of curved jaw coupling components on equipment in the United States that has been imported from overseas. (Note: Just like Lovejoy's L line, curved jaw couplings are manufactured, finished, and readily available from Lovejoy's Downers Grove, IL manufacturing facility.) While curved jaw couplings cannot be turned into jaw in-shear like straight jaw (due to their tooth profile), one nice feature of curved jaw couplings is that, by tightening their tolerance and using a very stiff elastomer, the curved jaw couplings can be turned into a very affordable backlash free coupling. (Backlash refers to the looseness of fit of a coupling, which is generally undesirable in very precise motion control applications.) 

Shear Loaded: In addition to the Jaw In-Shear couplings, there are several other popular elastomer in-shear designs. These popular designs include the tire (or tyre) coupling, and the sleeve coupling (or S-Flex coupling, pictured left). A common trait among all of these shear loaded designs is that system torque transmission will cease if/when the elastomer fails. In this capacity, the coupling is acting similar to a non-calibrated fuse. (Elastomers generally are not rated or designed to fail under specific load conditions, and should not be used or trusted to be a fuse. However, they are often designed as the weak point in a power transmission system... and will fail if there is a major system lockup. Solutions to include adding rated shear pins and/or a torque limiter to the coupling design are available if a user is looking/requiring their coupling to act explicitly as a fuse.)

Torsional: The third and final elastomeric coupling grouping to cover are torsional couplings. Mechanical power transmission systems can have devastating natural frequencies (think Tacoma Narrows Bridge Collapse). Diesel engine applications are one of the most common applications where natural frequencies need to be managed. The goal of a torsional coupling is to tune the system above or below its natural frequencies... and both torsionally soft (incorporating soft rubber) and torsionally hard (often incorporating hard plastics) are available to tune the system. 

Selecting the proper torsional coupling is not a trivial task (generally involves a formal torsional vibration analysis), and it is highly recommended that you consult with a coupling manufacturer's staff prior to making your own product selection. (Lovejoy offers multiple types of torsional couplings, and can be interchangeable with specific other manufacturers.)

Metallic (flexible) couplings - Metallic couplings are different from elastomeric couplings in that they do not employee elastomeric (soft) materials to provide coupling flexibility & dampening. The breadth of metallic coupling offerings is massive (covered in depth in The Coupling Handbook), and this post will focus in on and provide a quick cliff notes overview of the 2 major metallic flexible coupling product types: lubricated and non-lubricated.

Lubricated metallic couplings achieve flexibility through loose fitting parts rolling or sliding against one another, while non-lubricated metallic couplings achieve flexibility through a flexing or bending of a metal component itself. Lubricated couplings are generally less expensive, but do require periodic maintenance/more lubrication, and will eventually "wear out". Non-lubricated are generally more expensive, require minimal maintenance, and categorizes as having theoretical "infinite life" (no metal on metal wearing parts).  

(Note: While the Lovejoy brand is near synonymous with the elastomeric coupling market, the company has been a major player in the metallic coupling industry for several decades. Many people are surprised to learn that Lovejoy's metallic coupling sales are on par with Lovejoy's elastomeric coupling sales, and that their knowledge of the products and applications is so great.)

Lubricated Couplings: The three major types of lubricated metallic couplings are: gear, grid, and chain. The primary form of failure for these type couplings is wear (metal on metal contact), meaning torque peaks/overloads as well as poor or improper lubrication/grease maintenance will shorten the coupling's life.

Of the three major lubricated metallic coupling types, gear couplings (where misalignment is achieved through crowning on the gear tooth surfaces) are historically the big boy on the block. Gear couplings have a very high power density (can carry huge torque loads in a small footprint), have many available custom application options (i.e. - flanged or continuous sleeves, spacers, floating shafts, limited end float, sliders, insulation), can be balanced to operate at high RPMs, and are generally lower cost than other equivalent high torque coupling alternatives. Inclusive of Lovejoy, a number of manufacturers' flanged gear couplings are half coupling for half coupling interchangeable through size 9, given they adhere to the common AGMA standard (AGMA 9008-B00: Flexible Couplings -- Gear Type -- Flange Dimensions, Inch Series). Please remember, interchangeability does not mean coupling quality, reliability, ratings, or performance characteristics are equivalent... so please proceed cautiously when selecting a vendor.

Grid couplings (where misalignment is achieved between a single spring steel serpentine grid wrapped around two flanges) are also a very well respected lubricated metallic coupling. One advantage of this coupling is that the flexibility of the grid provides it an ability to spread out impact energy over time... allowing the coupling an opportunity to reduce the magnitude of peak loads. Grid couplings can be used in both horizontal and vertical axis applications, and also have may additional feature upgrades (floating shafts, break discs, spacers, etc.). Grid couplings generally compete with large elastomeric couplings (which may be too large to fit inside the system's space constraints), as well as with gear couplings (given the grid coupling's enviable all-metal ability to modestly dampen vibration). Most major grid coupling manufacturers (inclusive of Lovejoy) have kept the majority of their grid coupling components directly interchangeable... with the exception being unique seals and gaskets. (If interchanging manufacturers, corresponding seals and gaskets should be procured from the same manufacturer to avoid potential sealing issues). 

In contrast to gear and grid, chain couplings are somewhat of a dirty step child. In full disclosure, Lovejoy does not manufacture chain couplings... so we may be a bit biased... but, generically speaking, chain couplings are found and used on unsophisticated applications (i.e. - makeshift farming equipment). Chain couplings are known for being relatively rugged and very low cost. A chain coupling consists of two sprocket hubs with a single double roller chain connecting the two hubs. These couplings are relatively easy to install, maintain, and rough align.

Non-Lubricated Couplings: Popular non-lubricated metallic flexible couplings include the disc (or disk), diaphragm, link, spiral wound, bellows, and beam coupling types. All six have a theoretical infinite life (meaning they have no metal on metal wearing parts), assuming the flexing or load carrying methods stay within the mechanical endurance limits of the flexing metal material. (Overload on these type couplings, be it continuous torque or cyclic misalignment forces, will result in fatigue failure.) 

These couplings have been historically complex to understand and evaluate... as significant stress analysis (finite element analysis) must be conducted to flush out performance characteristics (inclusive of taking torque load, misalignment,  temperature, and varying system speeds into consideration). Non-lubricated couplings generally have a higher upfront cost, relative to traditional lubricated couplings, but can offer long term "total cost of ownership" savings opportunities.

Of all non-lubricated coupling types, disc couplings (with multiple layers of flexing discs) are the most popular... and they continue to pick up steam both in new designs (inclusive of boiler feed pumps, gas and steam turbines, compressors, high-speed test stands, marine propulsion systems, and wind energy) and in replacing traditional installed gear coupling applications (where either maintenance, reliability, or environmental concerns arise). Disc couplings can excel at high speeds (where balancing and lubrication concerns put gear couplings at a disadvantage), and, furthermore, have the built in advantage of no backlash which lubricated metallic couplings cannot claim). 

One drawback of disc couplings is that they are generally less tolerant of misalignment (queue smiles from the shaft laser alignment product sales folks). Without diving too deep into disc couplings, disc packs can be circular (call it version 1.0), flat sided (version 2.0), or scalloped (version 3.0) on the outer dimension... with each revision offering improved performance. (Circular disc packs acts as a beam... stressing the extreme edges, flat sided packs avoid the curved disc pack drawbacks, and scallop disc packs both avoid the curved disc pack drawbacks and provide more flexibility/misalignment handling capability. The additional capability can be attributed to the disc pack's reduced cross-section... which requires less force to flex, translating to lower reactionary loads on the system's adjacent bearings.) All three disc pack styles are readily available on the market (though Lovejoy only sells the scalloped version). 

Diaphragm couplings were originally introduced to service very high speed, high horsepower applications in the petrochemical industry... and has since progressed to other extreme applications such as helicopter drives. Diaphragm couplings handle misalignment through use of a flexing metal plate (or series of flexing metal plates in parallel). The metal plate(s) is loaded in shear, with torque being introduced at the outside diameter of the coupling and then transferred on to the inside diameter. (The process reversed at the opposite flex point.)

Diaphragm couplings are known for their large outside diameters, and, generally, very high cost. Diaphragm couplings are generally sold as custom solutions, and there are a wide variety of options to consider... so those seriously in the market for this coupling should spend a considerable amount of time speaking with manufacturers' application engineering staffs. (Note: Lovejoy does not sell diaphragm couplings, though Lovejoy does sell API 610 or 671 disc couplings that can sometime compete for the same application.)

Taking a huge step back from size and cost of diaphragm couplings, triple wound spring couplings are generally small and much more an off the shelf mainstream product (translation: Lovejoy has lots of these in stock). These couplings handle torques generally only up to ~1800 in-lbs, 213 Nm), with bores up to 1.5 inches (38 mm), and speeds up to 30,000 RPM. They operate by having three tension springs mounted (one inside the other) to the two shaft hubs. The middle spring runs in the opposite direction of the inner and outer spring to allow the coupling to transmit torque in either direction. As each spring can flex independently, both angular and parallel misalignment can be addressed with this coupling. This coupling does have both backlash and windup, but their values are known... so these couplings can be found in use on index positioning and robotic applications.

The three link couplings is variation/cousin to the traditional disc pack coupling, where two sets of three flat strip springs are attached to a triangular plate at the inner diameter and a circular flange at the outer. Links function similar to disc legs, only they are thick enough to be loaded in compression on one side and in tension on the other. With two flex planes, this coupling was designed for lightly loaded, high misalignment (up to ~5° angular) applications with smooth non-cyclic torque loads. 

In addition to disc couplings, bellows couplings (pictured left) and beam couplings (pictured below left) are considered well suited all-metal motion control couplings (Motion control applications include shaft encoders, resolvers, all forms of servo devices, linear and ball screw actuators, robots, step motors, light duty pumps and metering devices, plotters, medical equipment, positioning tables, computers and radar.) Key features/requirements for motion control couplings are their torsional rigidity, low inertia, constant velocity, low radial stiffness, zero backlash, corrosion resistance and the capability of cyclic (repeated start/stop/reverse) activity.

Bellows couplings use thin tubular metal bellows (either one or two layers) formed with annual corrugations as the flexing element, while beam couplings (pictured left) use a single piece of aluminum or stainless steel (generally bar stock) cut with single or double flex planes. While there are many similarities between bellows and beam couplings that make them both well suited for many common applications, one notable performance variance is that bellows couplings are generally more torsionally stiff than beam couplings (though beam couplings are also fairly stiff). 

In concluding this rapid 30,000 foot overview of flexible power transmission couplings, we would invite you to take a deeper dive into this subject matter (by reading "The Coupling Handbook")... and, of course, please don't hesitate to holler if we can be of any further assistance.