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Fluid Couplings

Hydrodynamic power transmission with soft start, overload protection, and vibration damping — constant-fill, variable-speed, and delayed-fill designs for mining, cement, and heavy-duty applications.

Anand Gears fluid coupling for soft-start power transmission

Power Transmission

Hydrodynamic Fluid Couplings for Smooth Power Transfer

Anand Gears fluid couplings deliver soft-start, overload protection, and vibration damping for heavy-duty applications in mining, cement, and industrial processing. Unlike rigid mechanical couplings, our hydrodynamic designs use a sealed chamber of viscous fluid to transmit torque progressively. An input impeller (pump) accelerates working fluid, which strikes the output runner (turbine), producing smooth, shock-free acceleration. Available in constant-fill (fixed soft-start), variable-speed (energy-saving load control), and delayed-fill (extreme soft-start for high-inertia loads) types. Power range 0.5 kW to 500 kW with torque transmission efficiency of 97%+ at synchronous speed. Compatible with standard IEC motors and easily integrated with gearboxes, crushers, pumps, conveyors, and fan drives.

Soft start — no electrical or mechanical shock to motor
Overload protection — slips on stall to protect equipment
Vibration damping — reduces torsional oscillations
No wear parts — sealed for maintenance-free operation
Energy efficient — variable-speed models reduce power at part load
Efficiency 97%+ at synchronous speed

Coupling Types

Fluid Coupling Variants

Three specialized hydrodynamic designs optimized for different load profiles — constant-fill, variable-speed, and delayed-fill configurations.

Constant-Fill Fluid Couplings

Maintains fixed fluid volume in working chamber for consistent soft-start characteristics and stable load transmission. Output speed approaches input speed asymptotically. Ideal for fixed-speed applications like mining conveyors, crushers, and mills where steady operation is required.

Slip Control Gradual, fixed soft-start
Best For Steady-load applications
Load Profile Constant or slowly varying

Variable-Speed Fluid Couplings

Uses a scoop tube or variable fill mechanism to control fluid volume dynamically. During light loads, coupling maintains reduced output speed, reducing power consumption and motor current draw. At full load, fluid volume increases, bringing output to synchronous speed. Energy-saving solution for applications with fluctuating loads — pumps, fans, mills.

Slip Control Dynamic, load-responsive
Best For Variable-load applications
Energy Saving 15–30% power reduction at part load

Delayed-Fill Fluid Couplings

Advanced design with time-delay fill mechanism that releases fluid gradually into chamber over several seconds as motor accelerates. Provides extreme soft-start for ultra-high inertia loads and massive flywheels. Dramatically reduces peak inrush current and mechanical shock. Used in kiln drives, heavy mill machinery, and large-volume pump systems.

Soft-Start Duration Adjustable, up to 30+ seconds
Best For High-inertia loads
Current Reduction Minimizes peak inrush current

Technical Principles

How Hydrodynamic Fluid Couplings Work

Fluid couplings operate on hydrodynamic principles using the Föppl circulation theory. Inside a sealed housing, an impeller (pump) is connected to the motor shaft, while a runner (turbine) is connected to the load shaft. The space between them is filled with viscous mineral oil at a controlled volume. As the impeller rotates at motor speed, centrifugal force accelerates the oil outward, creating a pressure gradient. The accelerated oil flows radially outward and strikes the runner blades, transferring kinetic energy and causing the runner to rotate. The oil then flows back through the center of the impeller, completing a continuous cycle.

At startup, when the runner is stationary, slip is maximum and the coupling acts as a speed reducer, producing high torque multiplication with a smooth, progressive rise in output speed. As the runner speed increases toward the impeller speed, slip decreases and torque transmission increases. At synchronous operation (output speed equals input speed), slip is minimal (typically 1–3%) and efficiency reaches 97%+ — nearly equivalent to a rigid coupling. The smooth transition from high-slip/high-torque startup to low-slip/high-efficiency steady-state operation, combined with the viscous damping properties of oil, produces the characteristic soft-start and vibration-damping benefits of fluid couplings.

Key Operating Characteristics

Soft Start (Acceleration Phase)

Motor accelerates unloaded to full speed in 1–5 seconds, then coupling gradually engages and transmits load. Typical inrush current limited to 2–3x full-load current (vs 5–7x for direct start).

Overload Protection

If output is stalled (e.g., belt jam), coupling continues to slip rather than stalling motor. Motor continues running at full speed while coupling transmits zero torque to load, preventing mechanical shock and motor damage.

Vibration Damping

Viscous fluid absorbs torsional vibrations and shock loads from the driven equipment, reducing vibration transmission to motor and bearings. Extends bearing life and improves equipment reliability.

Steady-State Efficiency

At full load and rated speed, slip is minimal (1–3%). Torque transmission efficiency is 97%+, allowing coupling to operate as a rigid coupling with only negligible losses.

Product Specifications

Fluid Coupling Performance Data

Standard performance specifications for Anand Gears fluid couplings across the full power range.

Coupling Type Power Range Max Torque Standard Speed Efficiency (Steady-State) Soft-Start Duration
Constant-Fill 0.5–500 kW To 3000 Nm 1450/1500 RPM 97%+ 2–5 seconds
Variable-Speed 1–250 kW To 2000 Nm 1450/1500 RPM 95%+ (at part load: 85–92%) 2–4 seconds
Delayed-Fill 5–500 kW To 3000 Nm 1450/1500 RPM 97%+ (at full engagement) 5–30 seconds (adjustable)

Standard Features

  • • Cast iron or ductile iron housing with finned design for heat dissipation
  • • Sealed bearing arrangement with grease lubrication (5000+ hour interval)
  • • ISO VG 46 mineral oil fill (customizable for high-temp applications)
  • • Elastomeric seals protecting against dust and moisture ingress
  • • Flexible coupling interface for connection to motor and gearbox
  • • Thermal expansion relief valve to prevent overpressure during operation
  • • Optional condition monitoring and oil analysis ports for predictive maintenance

Industry Solutions

Fluid Coupling Applications

Proven performance in mining, cement, chemicals, food processing, and power generation.

Mining Conveyors

Heavy-load conveyor systems transporting ore, coal, and aggregates. Constant-fill couplings provide soft start to prevent belt slip on incline, overload protection against spillage jams, and vibration damping to extend belt and pulley life. Enables longer conveyor runs and higher throughput.

Cement Mills

Rotary kilns and grinding mills with variable load profiles. Variable-speed couplings optimize energy consumption by reducing power draw during low-load periods (empty mill rotation, startup). Delayed-fill couplings manage extreme soft-start for massive kiln inertia during acceleration.

Crushers & Pulverizers

Jaw crushers, cone crushers, and impact mills processing hard materials. Overload protection prevents motor stalling on bridged material or tramp metal. Soft start reduces mechanical shock to crusher frame and bearings, improving reliability and reducing maintenance downtime.

Centrifugal Pumps

Large-capacity water, slurry, and process pumps. Soft start reduces water hammer in long suction lines, protecting pipes and pressure vessels. Overload protection handles sudden pressure spikes. Vibration damping reduces bearing wear and improves pump seal longevity.

Axial & Centrifugal Fans

Large HVAC fans in power plants, refineries, and industrial facilities. Variable-speed couplings reduce power consumption by 20–30% during partial-load operation (part-year cooling demand). Vibration damping extends bearing life in high-speed fan applications.

Sugar Mills

Cane crushers, molasses pumps, and boiling pans with variable seasonal loads. Variable-speed couplings save energy during low-throughput periods. Constant-fill couplings prevent belt slip under high crushing loads. Sealed design resists moisture and corrosion from molasses residue.

Pricing & Availability

Anand Gears Fluid Couplings are competitively priced for the Indian market. Pricing depends on power rating, coupling type, and customisation.

Starting From

₹8,000

Compact Units (2–5 kW)

Mid-Range

₹30,000

Standard Models (7–20 kW)

Industrial

₹1,25,000+

Heavy-Duty (30+ kW)

Prices are indicative and vary based on specifications. GST extra. Contact us for an exact quotation.

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Need a Fluid Coupling for Your Application?

Contact us for specifications and quotation. Provide motor power (kW), speed (RPM), load type (constant/variable/high-inertia), and application details. We'll recommend the ideal coupling type with technical data sheet and delivery timeline.

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