Short Answer:

A fluid coupling is a mechanical device that uses fluid to transfer power from one rotating shaft to another. It works without any direct mechanical connection by using the motion of a liquid, usually oil, inside a sealed casing. It provides smooth and controlled power transmission.

Fluid couplings are commonly used in automobiles, conveyors, pumps, and industrial machines where soft start and shock-free operation are needed. They help in reducing wear and tear, making machinery operation more reliable and efficient.

Detailed Explanation:

Fluid coupling

A fluid coupling, also known as a hydraulic coupling, is a hydrodynamic device used to transmit rotating mechanical power through a fluid medium. It provides a smooth and gradual transfer of torque from a driving shaft (like a motor or engine) to a driven shaft (like a conveyor or machine). This is especially useful in machines where sudden starts or stops can cause damage or mechanical shock.

The basic construction of a fluid coupling includes three main parts:

• Impeller (Pump) – connected to the input shaft
• Turbine (Runner) – connected to the output shaft
• Housing – contains the working fluid (usually oil)

The impeller rotates with the input shaft, creating a flow of fluid that imparts motion to the turbine, which in turn rotates the output shaft.

Working of a Fluid Coupling

When the input shaft turns the impeller, the fluid inside the coupling starts to move in a circular motion. This moving fluid carries energy to the turbine. As a result, the turbine begins to rotate and transmits power to the output shaft.

There is no rigid connection between the input and output shafts, which allows for slippage, making the system flexible. This slippage is especially useful during start-up because it allows the output to increase speed gradually instead of suddenly.

Where It Is Used

1. Automobiles
   Fluid couplings are widely used in automatic transmissions of vehicles. They allow the engine to keep running even when the vehicle is stopped, and provide a smooth acceleration without jerks.
2. Conveyors and Crushers
   In industries like mining or cement, where large machines operate under heavy loads, fluid couplings help in starting the equipment slowly, protecting motors from overloading.
3. Pumps and Fans
   Large centrifugal pumps and blowers use fluid couplings to ensure shock-free starting, reduce vibration, and avoid sudden overload.
4. Marine and Rail Systems
   Ships and locomotives use fluid couplings for controlling torque and providing smoother mechanical drive.
5. Textile and Paper Machines
   These industries use fluid couplings in long-length shaft systems to achieve flexible and noise-free operation.

Advantages of Fluid Coupling

• Protects machinery from sudden shocks
• Allows smooth start-up
• Requires less maintenance compared to mechanical clutches
• Reduces mechanical wear and tear
• Acts as a torque limiter in overload conditions

Conclusion:

A fluid coupling is a simple and effective device used for power transmission between rotating shafts through fluid motion. It is mainly used where a smooth, controlled, and flexible start or stop is needed, such as in vehicles, conveyors, pumps, and heavy machines. It increases machinery life, improves safety, and enhances operational efficiency in civil and industrial applications.