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.