Dear Shri Rekhawar,

There are various types of fluid couplings to suit belt conveyor applications, such as traction type, traction type with delay fill chamber, traction type fluid coupling with enlarged delay fill chamber, traction type fluid coupling with three chambers, fill controlled turbo fluid coupling, scoop type coupling, etc.

The couplings have differing characteristics which permit different magnitude of starting time i.e. degree of softness of the start. The starting stress in the belt occurs as per the starting factor from the drive unit (including fluid coupling). Therefore, use of particular type of fluid coupling is related with total design of belt conveyor.

If you want to change the type of fluid coupling, it should be preferably done after checking the tensions in the belt, load on pulley etc.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

In addtion, there may be electrical power side and motor issues.

A scoop type coupling will permit the motor to be started quikcly and without load on the acceleration to full speed ie minimal starting current and time.

James ■

Dear Rekawar:

Yes, you can easily replace the scoop with a simple delay chamber from the details provided. This assumes the belt is not highly inclined such that the running power is near the motor nameplate.

You have not identified enough to provide an accurate and informed position, so take these suggestions with some wisdom.

Assuming the lift from head to tail is only about 10 m. This is enough for some terrain difference plus head station transfer. When we take a guess at , lift, idler spacing, idler details, material density, and other key factors, the following is found:

1. 30 sec start requires about 90% of 250 kW

2. 25 sec start requires about 95% of 250 kW.

This timing to accelerate is within the couplings heat rating, given it is balanced to the motor. How many starts and other important factors need review before you leap.

So, we ask why would an engineer select a more expensive, more complex, more maintenance prone, and less reliable scoop coupling over your interest? Maybe, you have not supplied all information.

The scoop takes about 2 seconds to react to conveyors mechanical resistance. The motor will achieve full speed before 2 seconds. Thus, the motor will start under no conveyor load, only the drive inertia. The power voltage drop would have to be quite severe to be a factor, but it should be checked.

Lawrence Nordell

www.conveyor-dynamics.com ■

Dear rekhawar,

as some of the responses state already:

in most of the cases it is possible to replace scoop tube coupling with a constant filled coupling with delay chamber.

But following has to be taken into consideration.

1. Mass moment of inertia to be accelerated.

If inertia is high this would 'heat up' the coupling more - there is the limit of a constant filled coupling. So in that case a filled controlled coupling may be prefered (as it is installed).

2. Depending on the design of the coupling the start-up could be made softer. In the following sequence coupling get a better start-up function in order to protect the belt:

constant filled (cf)

cf with delay chamber

cf with enlarged delay chamber

cf with enlarged delay chamber and additional annular chamber

fill-controlled scoop tube (open loop system)

fill-controlled (closed loop system)

3. Constant filled couplings reduce during start-up of motor the transmitted torque (torque is a function of speed^2).

Fill-controlled couplings give a nearly load free start-up of the motor as the working circuit is empty.

For exchange of coupling to a constant filled type motor must still be able to start-up with higher load.

Above listed points result in checking in detail the requirements of the belt conveyor, as main point start-up time respectively start-up factor to protect belt and motor during start-up.

For further information kindly contact us or visit our homepage:

http://www.startup-components.com ■

Dear Rekhawar

I only use Scoop (or drain) couplings when I really have to.

This is when I do not want variable speed but I do need a very soft start, and the start time is very long.

The start time is often the important bit as a traction coupling is limited to a relatively short start time. The scoops can have almost infinite start times with external cooling. This is handy for very long conveyors.

Electrical soft starts are rapidly replacing scoops and drains for this application.

For your application however, your scoops can definitely be replaced by traction couplings. Here the TSS ones are the best.

Use TSS 562 with oil fill to about 11.5 to 12 bolts from vertical, and it will be just fine.

Good luck ■