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Understanding A Fluid Coupling

A fluid coupling is a simple device that connects the prime mover to a driven machine where the driven machine can be a fan, pump, blower, conveyor, or a crusher. A fluid coupling is used in almost every industry. For example, it can be used in power generation, mining, quarrying, and steel production.

How a coupling works

A fluid coupling consists of two elements: impeller and runner. The impeller is connected to a prime mover while a runner is connected to the driven machine. These two elements are positioned face to face and they are placed inside a casing which is usually filled with a number of fluids.

When the motor is rotated, the fluid in the casing is picked up in the vanes of the impeller and it’s thrown outwards towards the vanes of the runner. When the fluid hits the runner, the runner begins to rotate and drives the driven machine.

Types of fluid couplings

Constant fill fluid coupling: this device is characterized by three elements: driving impeller (pump) that is mounted on the input shaft, driven impeller (turbine) that is mounted on the output shaft, and cover that is flanged to the output impeller.

For proper functioning of the device, a slip is essential. The formula for the slip is:

Slip%= ((input speed-out speed) /input speed) X 100.

In normal conditions the slip varies from 1.5% to 6%.

Variable fill fluid coupling: this device has a very simple and effective working mechanism. Oil is pumped from a pump through a heat exchanger to the hydrodynamic coupling circuit where it’s drained off through a number of orifice plugs. By controlling the rate at which oil flows into the circuit, the working of the coupling is greatly altered.

In addition to a simple working mechanism, this device also has a number of other advantages such as: soft starting, accurate speed variation, vibration dampening, and overload protection.

Hydraulic couplings: they are used for fast and easy connection and disconnection of hydraulic circuits, forest, agricultural and other machinery and equipment. The good thing with these devices is that they are very effective in their working. Installation of the devices is very easy.


This is what you need to know about fluid couplings. Regardless of the device that you go for, you should ensure that you buy from reputable sellers. This way you will be assured that you are buying a high quality devise.


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