Fluid clutches

Fluid clutches

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Fluid clutch or hydraulic coupling is a hydrodynamic device used for rotating mechanical power transmission. In fluid coupling, there is no mechanical contact between driving shaft and driven shaft. It transmits power from one shaft to another with the help fluids or oils.

Construction of hydraulic coupling

Hydraulic clutch consists of a pump impeller and turbine runner, which are identical in shape, completely housed in an oil filled casing. Typically mineral oil is used as working fluid. The pump impeller (primary wheel) is connected to the drive shaft (input shaft), and the turbine runner (secondary wheel) is connected to the driven shaft (output shaft). Both shafts are in coaxial. Both pump impeller and turbine runner have vanes to guide fluid flow direction. The wheels are facing each other with very narrow clearance between them.

Application of Fluid clutch

Hydraulic coupling has many application in industrial machines and locomotives. They are used in mining, textile industries, oil and gas industries and other material handling industries. Fluid coupling can be used in very extreme condition like high engine vibration. The fluid utilized in the coupling can successfully absorb such vibration, so they are best for cyclic loading conditions. The fluid coupling can also act as a hydrodynamic break.

Advantages of Fluid clutch

Controlled start up speed without shock loading of power transmission system.
There is no mechanical contact between driving shaft and driven shaft (or between pump wheel and turbine wheel). Hence there is no frictional wearing of them.
Power transmission is smooth. Motor or engine starts unloaded.
Fluid coupling can dampen shock loads. Fluid coupling can run smoothly even in extreme conditions.
The power transmission is free from vibration. There is no chance of vibration noises when power transmitted from vibrating engine to the driven shaft by using a fluid coupling.
Fluid coupling can be used in both vertical and horizontal application.
In case of overloading, it can disengage from driver by automatically draining the oil filled by blowing of fusible plug
The maximum torque can be adjusted by varying the amount of oil filled in the casing.

Disadvantages of Fluid clutch
There is always slip. There is always slight difference in speed of pump wheel and turbine wheel
The fluid filled in casing must be compatible with coupling component, it directly affects the transmission behaviour of the fluid coupling.
Fluid coupling cannot develop torque when the driving shaft and driven shaft are rotating in same angular velocity.
Under stalling condition, the coupling dissipates energy as heat it may lead to damage.