Coupling Selection How to Select The fluid coupling is a multiple-use device: • Provides soft, cushioned starts • Provides increased starting torque • Provides overload protection • Reduces current draw when starting • Provides load balancing for multiple drives • Provides load dampening To achieve these objectives, use a standard NEMA B motor with sufficient breakdown torque to start the machinery and with adequate continuous rating for the normal continuous load. The function of the fluid coupling is to allow the motor to come up to speed with minimum load. The fluid coupling is selected on the basis of the full load running horsepower as well as the torque required to start the load. In some applications, such as belt conveyors, it may be desirable to limit the maximum starting torque. If possible, select the coupling on the basis of the load rather than the motor rating, especially if the motor is oversized. Couplings that are selected on the basis of the motor size will have starting torque and maximum overload torques in relation to the motor rating. Selection Procedure 1. Determine the running load horsepower (preferred) or the motor horsepower. 2. Choose a Start Factor from the Table below. Start Factor: the ratio of a pertinent starting torque to the running load torque (the torque required to maintain the load (speed) once equipment has been accelerated to its design speed). For belt conveyors select from pages 14 and 15. Start Factor is the average starting torque exerted by the fluid coupling during load acceleration, expressed as a percent of running load torque. Page 15 (HFDD) also states initial start factor, which is the nominal torque applied at the inception of acceleration, expressed as a percent of running load torque. The low initial start factor (HFDD) assures an extra soft empty belt start on low inertia conveyors, yet is adequate to overcome the breakaway torque of the conveyor. For general duty (other than belt conveyors), select from pages 16 thru 19. Start Factor is equivalent to the initial start factor mentioned in the paragraph above. For these general duty applications, the initial start factor ensures breakaway of the driven machinery. Start Factor Table Applications Belt Conveyors Fans Mixers Crushers Armored Face Conveyors Start Factor 120% to 140% General Duty 140% 170% to 200% 250% Refer to the Factory Select From pages 14-15 pages 16-19 pages 16-19 pages 16-19 Refer to the Factory 3. Refer to the Quick Selection tables (pages 14 thru 19). For belt conveyors, select HFN or HFD from page 14. For extra soft empty belt starts on low inertia belt conveyors, consider HFDD selections on page 15. For general duty (other than belt conveyors), select HFD or HFN/HFR from pages 16 thru 19. Note the percent slip and fill angle. 4. Select one of the Mounting Arrangements (gear coupling, disc coupling, etc.) from page 12. 5. For coupling size, basic type, and mounting arrangement selected, see Availability Table, page 13. This table indicates whether the selection is available and, if so, the allowable speed. 6. If the initial basic type and mounting arrangement are not available or there is insufficient allowable speed, consider an alternative basic type/mounting arrangement. 7. Check bore capacity of the coupling selected from the dimension tables, pages 20 thru 29. Selection Example: 1. Belt Conveyor: Fluid coupling connects a motor to the input shaft of a gear drive. Motor is NEMA B, rated 100 hp at 1775 rpm. Running load = 98 hp. Motor shaft 2.875", gear drive input shaft 2.250". 2. With the Start Factor 120% to 140%, select from pages 14 and 15 as appropriate (selections for belt conveyors). 3. Use HFD selections for belt conveyors, page 14. For 98 hp running load, select 370HFD, 4.1% slip, fill angle 63 degrees. 4. Select 370HFD20 (gear coupling mount) from page 12 – economical and includes drop-in/drop-out servicing. 5. From the Availability Table, page 13, 370HFD20 is available, allowable speed is 1800 rpm, exceeds the requirement of 1775 rpm. 6. Alternative basic type/mounting arrangements are listed on page 13. 7. From page 21 dimensions, max bore is 2.875", which is adequate. (521-110) 11
