Dear engineers would you please help me about belt driven motor? i would like to know what happen for fans in ventilation system ( i mean their efficiency) if we change single revolution pully to dual revolution therefor the motor can work with two speed : low speed and high speed . I f we do that what can we do for tightening the belt ? Mary
Dear John OBrien I dont understand what you said . would you please tell me what do you suggest for me ? Thanks alot Azadeh
If you change speed by moving the belt to a smaller pulley, the belt will not be tight unless you have a "take-up" of some sort. What I think he means is an idler pulley on a spring-loaded lever; it will keep the belt tight. Such a device might be called a "tensioner". Look to the web sites that supply Power Transmission Components.
You can put the same two different pulleys on the motor and on the fan. Then when you change they have the same length. This is common on simple drill presses where one belt may select different speeds. But this is a manual change. You did not say you wanted an automatic means. You did not describe the belt type. There are many. Efficiency is terrible with v shaped belts and sheaves, but toothed timing type belts are much better. A timing belt is unsuitable for transferring between different pulleys.
Hello engineers Thank you for all your answers . I should examin your susggestion .Transmission and inverters are expensive . There is one vbelt (simple belt without tooth) with 2different size pulley, and i will move the belt manually to change the speed(slow-fast) . the problem is the belt isnt tight and it seems i should use belt tightner(sth to take up on belt) or... i dont know.... Best regards Mary
Dear John OBrien I dont understand what you said . would you please tell me what do you suggest for me ? Thanks alot Mary
A "take u"p means some way to control the looseness of the belt - a tensioner. This can be as simple as a third pulley on an arm in the middle of one side of the belt - called an "idler." The the rotational axes are horizontal then you can simply hang a weight on the "idler" pulley. If a weight cannot be used then a spring is simple to use. Google on "belt drive idler" then look at the images. You may wish to consider a flat, grooved belt; they are more efficient. But, v belts are common everywhere and inexpensive.
If you have two different size pulleys on one shaft, you will also need two pulleys on the other shaft, otherwise they will be misaligned. In this case you might as well have different sizes so the total belt length is unchanged. If the shafts are far enough apart you might get away with it, then you either need an adjustable idler pulley, or the motor needs to be on a moveable mount to take up the difference. You would need a way to adjust the tension even if there's only one pulley on each shaft.
