Regal Rexnord
Fluid Couplings
Regal Rexnord fluid couplings are hydrodynamic drive components that use the kinetic energy of a fluid(typically mineral oil or water) circulating between a pump impeller(connected to the motor) and a turbine runner(connected to the load) to transmit torque with no mechanical contact between the driver and driven shafts.This fluid - based power - transmission principle provides three primary benefits unmatched by mechanical couplings: soft, controlled acceleration of high - inertia loads that protects motors from stall and reduces mechanical shock; built -in torque limiting that isolates the drivetrain from overload damage; and natural vibration isolation between the motor and driven equipment.Plant engineers in mining, aggregate processing, material handling, and power generation specify Regal Rexnord fluid couplings — manufactured under the Stromag and Rexnord brands — when they need to start a fully loaded conveyor, crusher, or mill without oversizing the motor for starting torque, or when they must protect expensive, inaccessible equipment from the torque spikes caused by jams, stalls, or sudden load changes.Available in constant - fill and variable - fill(scoop - controlled) designs, with power capacities from fractional kilowatts to several megawatts, our fluid coupling portfolio provides the controlled - start and torque - limiting capabilities that enable safe, efficient operation of the world’s largest bulk - material handling and processing systems.
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Soft, Controlled Load Acceleration
Fluid - coupling slip during startup limits motor inrush duration and lets the driven load accelerate smoothly, reducing belt tension spikes, gear - hammer impact, and structural stress on conveyor and crusher frames.
Inherent Overload & Stall Protection
During a jam or stall, the fluid coupling slips without transmitting damaging torque to upstream equipment — converting excess energy to heat that can be dissipated or, in extreme cases, safely discharged via fusible - plug release.
Motor Sizing Optimization
By uncoupling motor starting requirements from load inertia, fluid couplings allow the use of smaller, less expensive, and more energy - efficient motors that are sized for running torque rather than breakaway torque.
Vibration Isolation Between Driver & Load
The fluid mass provides near - perfect isolation of torsional vibrations between the motor and the driven machine, protecting gearboxes and bearings from motor - side vibration and vice versa.
Multi - Motor Load Sharing
On dual - drive conveyors and mills, fluid couplings naturally balance the load between two or more motors by allowing minor speed differentials — no complex electronic load - sharing controls required.
Variable - Fill(Scoop) Control for Process Flexibility
Scoop - tube - controlled variable - fill couplings allow operators to adjust the output speed of a fixed - speed motor, providing the process flexibility of a VFD without the power electronics.
Fluid Couplings vs.Variable Frequency Drives for Conveyor Start Duty
The choice between fluid couplings and VFDs for starting and controlling large conveyors involves capital cost, operational simplicity, and reliability tradeoffs.Fluid couplings offer a purely mechanical, grid - independent soft - start that requires no control programming, no cooling infrastructure, and no harmonic filtering — and they provide inherent overload protection that no VFD can match without complex torque - limiting algorithms.For remote, unstaffed mining installations where electrical infrastructure is limited and maintenance skills are mechanical, the simplicity and reliability of a fluid coupling are compelling advantages.VFDs, by contrast, provide continuous speed control beyond just starting, enable regenerative braking for downhill conveyors, and offer energy savings when the conveyor operates at varying speeds or partial loads.In many large - conveyor installations, Regal Rexnord engineers design hybrid systems: fluid couplings for the controlled start and overload protection, with the balance of conveyors on the same site using VFDs where speed control adds value.This multi-technology approach matches the solution to the specific operational requirements of each conveyor, avoiding the pitfalls of a single - technology mandate.
Fluid Coupling Maintenance, Fluid Selection & Fusible - Plug Safety
Proper fluid selection and level maintenance are the key determinants of fluid coupling service life and performance.Regal Rexnord recommends specific mineral - oil grades with the viscosity, thermal stability, and anti - foaming characteristics required for hydrodynamic power transmission — not standard hydraulic or gear oils.Fluid level must be maintained within the specified range: overfilling reduces slip and soft - start benefit while increasing steady - state operating temperature; underfilling causes excessive slip and overheating that can activate fusible plugs.Fusible plugs are a critical safety element designed to melt at a specified temperature and safely release the fluid charge before internal pressure can cause a casing rupture — their replacement with non - OEM plugs of unknown melting temperature is among the most dangerous field modifications possible on a fluid coupling.Regal Rexnord offers fluid - analysis programs, ultrasonic level - checking equipment, and on - site maintenance training that equip plant teams to manage fluid couplings safely and effectively, achieving the decades - long service life that makes them the lowest - total - cost starting solution for severe - duty conveyors and crushers.