Lovejoy SX 158-6 Disc Coupling, SX-6 Series

Lovejoy SX 158-6 is the 158-6 size of the SX-6 industrial disc coupling: two hubs, a stock-length spacer and two unitized six-bolt disc packs. It is rated 17,700 in-lb (2,000 Nm) nominal and 35,400 in-lb (4,000 Nm) peak, with bores to 2.76 in (70 mm), and is built to run without lubrication in drives that need torsional rigidity and no backlash.

Two flex planes for parallel, angular and axial offset

The SX type has a flex plane at each disc pack, so parallel misalignment is taken up by angular deflection in the two packs, in addition to angular and axial movement within the stated limits. Lovejoy developed its disc pack profile with finite element analysis and states that the pack accommodates one half to one and a half degrees of angular misalignment. Packs are made of AISI-301 stainless steel, and condition can be inspected with a strobe light while the machine is running.

The catalogue lists these advantages: no lubrication or coupling maintenance, no wearing parts, inspection without disassembly, high power density, resistance to harsh environments and long life when properly sized and aligned. SX couplings are assembled on the equipment at installation, and custom spacer lengths can be made.

Technical specifications

SX-6 sizes

Nominal torque and maximum bore across the six-bolt range:

Eight-bolt sizes 278-8 to 570-8 transmit more torque (177,000 to 2,292,300 in-lb) but accept less angular misalignment, 0.5 degree per pack.

Selecting the size

Calculate application torque and multiply by the service factor from catalogue page D-7; the worked example uses 3.0 for a three-cylinder reciprocating air compressor driven by a 225 HP motor at 1,150 RPM. Choose a size whose nominal torque exceeds the selection torque, then confirm shaft diameters, shaft separation and the unbalanced speed limit. Where larger bores are needed, the next size up may be chosen even if torque is over-rated.

The related types are SU (single flex plane, angular and axial only), SXC close-coupled, SXCS and SXCST split-spacer styles, and the DI drop-in design, which Lovejoy says is designed to meet the balance and anti-flail requirements of API-610.

Installation and operation notes

Lovejoy recommends installing at roughly 20 percent of the allowable misalignment. Allowable parallel offset is the tangent of the angular limit multiplied by the distance S between the disc packs; derived for this size, tan 1.5 degrees x 4.00 in is about 0.105 in. Do not operate without coupling guards. Tighten disc pack bolts to the values Lovejoy specifies and check them after the first run.

Where it is used

Disc couplings suit compressors, pumps, fans and gearbox drives where torsional rigidity matters and lubricated grid or gear couplings are a maintenance burden. Compare with the API 610 Dodge StratoLink disc coupling.

Operating notes for Oman and the GCC

Disc couplings are used on pumps, compressors, fans and generators in oil and gas, power and water plants, where a coupling with no lubrication and no backlash is preferred. Because the disc packs are stainless steel, they suit humid coastal sites better than many plain-steel designs, but bolts and hubs should still be checked for corrosion during maintenance. Check the disc packs with a strobe light while running, and look for cracks or loose bolts at each shutdown.

Information to send with an enquiry

• Machine power, speed and duty
• Shaft diameters and keyways on both sides
• Shaft separation and spacer length
• Any API or client specification that applies

Frequently asked questions

What is the SX 158-6 coupling?

A two-flex-plane disc coupling with two hubs, a spacer and two unitized disc packs, six bolts per pack, rated 17,700 in-lb (2,000 Nm) nominal.

Does it need lubrication?

No. Lovejoy lists elimination of lubrication and coupling maintenance, no wearing parts and torsional rigidity without backlash among the advantages.

What misalignment can it take?

Axial 0.122 in (3.1 mm) for the two packs and 1.5 degrees angular per disc pack on this size; parallel offset follows from the angular capability times the distance between packs.

How are the disc packs made?

From AISI-301 stainless steel, as unitized packs, which Lovejoy says gives high strength, fatigue endurance and resistance to most environmental conditions.

Can it protect against over-torque?

Overload bushings are available to protect the disc pack from momentary torsional overloads and allow a shorter shaft separation.

Documents and quotation

The Lovejoy disc coupling catalogue section is hosted on this page. See Couplings and Shaft Locking Devices. Seven Star LLC is an independent supplier in Muscat; send size, bore and keyway data, BSE and balance requirements for a quotation.