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Brand: Lovejoy
Lovejoy SIER-BATH FHSA 3 High-Speed Gear Coupling
Description
Lovejoy FHSA 3 is size 3 of the SIER-BATH FHSA High Speed Standard gear coupling: a spacer-type alloy-steel gear coupling rated 68,000 in-lb (7,680 Nm) and 15,000 RPM, with a maximum bore of 3.0 in (81 mm metric keyway) and a standard 5 in (127 mm) shaft separation. It is built for turbomachinery drives where balance and gear-tooth precision matter more than catalogue convenience.
A high-speed gear coupling for turbomachinery
The Lovejoy SIER-BATH F Series high-speed gear couplings are designed for exacting high-speed, high-efficiency performance beyond the ranges and limits of standard coupling specifications. Typical applications are high-speed centrifugal and axial flow compressors, gas turbines, steam turbines and test stands. The FHSA type is the high-speed standard grade between the close-coupled FHS and the precision FHSAA and ultra-precision FHSPAA types, with FHSMA for marine and FAC for centrifugal pumps.
Lovejoy lists these features: dynamic balancing, weigh-balanced fasteners, body-fitted bolts in reamed holes, precision-manufactured close tolerances, a piloted gear fit, and hubs, sleeves and spacers in alloy steel. Gear teeth can be nitrided; for the FHSA the catalogue specifies Class AN with a surface hardness of 85.5 minimum on the Rockwell 15N scale.
Technical specifications
| Parameter | Specification |
|---|---|
| Size | FHSA 3 |
| Torque rating | 68,000 in-lb (7,680 Nm) |
| Maximum speed | 15,000 RPM |
| Maximum bore, square keyway | 3.0 in |
| Maximum bore, metric keyway | 81 mm |
| Nominal BSE | 5 in (127 mm) |
| Weight, complete coupling at maximum bore | 56.0 lb (25.4 kg) |
| Moment of inertia WR2 / GD2 | 325.0 lb-in2 / 3.7 Nm2 |
| Torsional stiffness | 18.3 x 10^6 in-lb/rad (2.07 x 10^6 Nm/rad) |
| Maximum angular misalignment | 1/2 degree |
| Overall length (OAL) | 12.19 in |
| Spacer dimension S | 4.81 in |
| Hub length through bore (LTB) | 3.59 in |
| Flange diameter (FD) | 8.38 in |
| Dimension D / HD | 4.69 in / 4.25 in |
| Flange bolts | 10 off, 1/2 in |
| Core hardness | HRC 30-35, magnetic particle inspected |
FHSA sizes 1.5 to 6
| Size | Torque rating | Max RPM | Maximum bore |
|---|---|---|---|
| 1.5 | 12,600 in-lb (1,420 Nm) | 18,000 | 1.5 in (38 mm) |
| 2 | 22,600 in-lb (2,550 Nm) | 17,000 | 2.0 in (52 mm) |
| 2.5 | 46,600 in-lb (5,270 Nm) | 16,000 | 2.5 in (65 mm) |
| 3 | 68,000 in-lb (7,680 Nm) | 15,000 | 3.0 in (81 mm) |
| 3.5 | 135,500 in-lb (15,310 Nm) | 14,000 | 3.5 in (95 mm) |
| 4 | 209,900 in-lb (23,720 Nm) | 13,000 | 4.0 in (107 mm) |
| 4.5 | 310,700 in-lb (35,110 Nm) | 11,000 | 4.5 in (114 mm) |
| 5 | 441,000 in-lb (49,830 Nm) | 10,000 | 5.0 in (137 mm) |
| 5.5 | 590,500 in-lb (66,720 Nm) | 9,600 | 5.5 in (150 mm) |
| 6 | 731,000 in-lb (82,600 Nm) | 9,000 | 6.0 in (162 mm) |
Selecting a high-speed gear coupling
These couplings are engineered per application: provide power, speed, shaft diameters and keyways, BSE, balance grade and any API or customer specification so that Lovejoy can confirm the spacer length, balance and nitriding class. The catalogue gives a method for finding the torsional stiffness when the spacer is longer or shorter than standard: for a spacer n inches longer, 1/kx = 1/ks + n x 1/ki, where ks is the stiffness of the standard coupling and ki that of one inch of spacer body; for a shorter spacer the sign changes to minus.
Related sizes are tabled for FHS close coupled, FHSAA precision, FHSPAA ultra precision, FHSMA marine and FAC centrifugal pump couplings in the same catalogue section.
Installation and operation notes
High-speed gear couplings are matched sets: components are not interchangeable between units, so keep match marks and mount the assembly as supplied. Fasteners are weigh balanced in sets; replace them only with correct balanced sets. Lubrication, alignment and bolt torque must follow the manufacturer instructions, and the catalogue warns not to operate with improper alignment and to recheck if the coupling vibrates or beats.
Matching and ordering data
Because the FHSA is a matched, balanced assembly, an order should state the size, the bore and keyway for each shaft, the shaft separation, the operating speed, the torque and any balance or nitriding requirement. Lovejoy then confirms the spacer dimension and component set. The maximum bore depends on the keyway standard, so always confirm the finished bore against the table before machining or fitting hubs. Misalignment capability is limited to the figure in the table, so alignment of the driver and driven machines should be checked cold and hot.
The FHSA 3 figures here are catalogue data for the standard configuration; special lengths, materials or balance grades are handled as engineered options.
Where it is used
Compressor trains and turbine-driven machinery in gas processing, power generation and petrochemical plants are the typical home of this grade. Compare with the standard-duty Flender ZAPEX gear coupling or the API 610 Dodge StratoLink disc coupling for pumps.
Operating notes for Oman and the GCC
High-speed gear couplings are found on compressor, turbine and generator trains in gas processing, refining, petrochemical and power plants in the region. These couplings are usually specified to the machine maker’s data and the end user’s specification, so replacements should be ordered with the original coupling data, balance requirements and lubrication method. Check the lubrication system, seals and alignment at each planned outage.
Information to send with an enquiry
- Equipment train, speed and power
- Shaft ends, shaft separation and any existing coupling data
- Balance grade and lubrication method required
- Any API 671 or other specification named in the purchase order
Frequently asked questions
What is the FHSA 3?
Size 3 of the Lovejoy SIER-BATH FHSA High Speed Standard gear coupling: an alloy-steel spacer gear coupling, rated 68,000 in-lb (7.68 kNm) and 15,000 RPM.
How is it balanced?
Lovejoy states the couplings are dynamically balanced as assemblies and match marked, with fasteners weigh balanced in sets; components are not interchangeable between units.
What material is used?
Alloy steel with a core hardness of HRC 30-35, magnetic particle inspected, with ground bores; nitrided gear teeth can be specified as Class AN.
What are typical applications?
High-speed centrifugal and axial flow compressors, gas turbines, steam turbines and test stands, per the catalogue overview.
What misalignment is allowed?
The FHSA table lists a maximum angular misalignment of 1/2 degree on the sizes shown.
Documents and quotation
The Lovejoy high-performance gear coupling catalogue section is hosted on this page. See Couplings and Shaft Locking Devices. Seven Star LLC is an independent supplier in Muscat; send the duty, speed, shaft data and specification for a quotation.
Datasheets & Documents
- Datasheet Lovejoy high-performance gear coupling catalogue section (FHS to FAC types) Download
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About brand
Lovejoy is an American maker of industrial couplings and power transmission products, based in Downers Grove, Illinois. Thomas Lovejoy founded the company in Chicago in 1900 to make tooling for the railroad and steel industries; in 1927 it bought Louis Ricefield's patent for the jaw coupling, which became its core product. Timken acquired Lovejoy on 8 July 2016.
Lovejoy company profile
| Founded | 1900, Chicago, by Thomas Lovejoy |
|---|---|
| Headquarters | Downers Grove, Illinois |
| Ownership | The Timken Company, since July 2016 |
| Key product | Jaw coupling, patent bought in 1927 |
| Product families | L-type and CJ curved jaw couplings, jaw in-shear couplings, S-Flex and Quick Flex elastomeric couplings, SX disc couplings, grid and gear couplings, universal joints |
Milestones
- 1900: Thomas Lovejoy founds the company in Chicago.
- 1927: Lovejoy buys the jaw coupling patent.
- 1960s: Universal joints and variable speed pulleys are added.
- 2016: Timken acquires Lovejoy.
Couplings and universal joints from Lovejoy
The Lovejoy range includes jaw and jaw in-shear couplings, S-Flex and Quick Flex elastomeric couplings, curved jaw couplings, HercuFlex and high-speed gear couplings, disc couplings and grid couplings, together with Curtis block and pin universal joints.
Lovejoy products at Seven Star LLC
Seven Star LLC lists Lovejoy coupling families with catalogue data, torque ratings and bore tables so that engineers can match a coupling to a drive. Send the shaft sizes, torque, speed and misalignment for a quotation.
Lovejoy products we list
Facts checked against Lovejoy's own history page and Timken's 2016 SEC filings, October 2026.
Related products
Frequently Asked Questions
What is the FHSA 3?
Size 3 of the Lovejoy SIER-BATH FHSA High Speed Standard gear coupling: an alloy-steel spacer gear coupling, rated 68,000 in-lb (7.68 kNm) and 15,000 RPM.
How is it balanced?
Lovejoy states the couplings are dynamically balanced as assemblies and match marked, with fasteners weigh balanced in sets; components are not interchangeable between units.
What material is used?
Alloy steel with a core hardness of HRC 30-35, magnetic particle inspected, with ground bores; nitrided gear teeth can be specified as Class AN.
What are typical applications?
High-speed centrifugal and axial flow compressors, gas turbines, steam turbines and test stands, per the catalogue overview.
What misalignment is allowed?
The FHSA table lists a maximum angular misalignment of 1/2 degree on the sizes shown.
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