Re-Size Calculation of Pulley

Well AP, a guy like me would feel lucky to get a fan that exceeded designed throughput; and looking at it in that light I don't think pulleys and gears will be of much help; unless you intend to dump the power difference between the higher rate of moving air and the lower rate of moving air.

Perhaps you would meet with more success by controlling power input instead of changing mechanical ratio.

I believe it is quite possible that if what you need is an electric motor power controller then the sponsors of this site, and the folks within, can probably fix ya right up.

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Thanks to all, I have no option to controlling power input to change motor rpm. first and last option is change size of pulley of motor or fan. If any body have thumb rule or any equation to calculate re-size of pulley. kindly help to solve problem.

If you increased the size of the motor pulley, you might overload the motor. Making the load (blower pulley) larger would do the same. If you took off the blower pulley, and replaced it with a smaller one, the load will go down. No overload at all. I think Solar Eagle supplied an excellent link which shows this.

No need for complex electronics.

The motor must be sized to handle the load, if you reduce the load you may have to reduce the motor output....by following the calculations in the link you can determine what will work....

Thanks to all dears and also to SOLAR EAGLE, I will made modification accordingly and to be confirmed result very soon.

Thanks for your support, the Blower is centrifugal type and running with heavy air cutting noise due to almost double air quantity. I wants to know how to calculate re-size of blower or motor pulley to reduce the air qty at nearest design.

I believe the opening post is stated incorrectly.

It should read "air handling unit was improperly selected or specified by me".

It's obvious.

You should contact the supplier and ask for help. Let them do a proper analysis and select the correct pulley/pulleys.

Dear Friend,

You know that The Basic Fan Equation involved for the Fan is

CAPACITY is PROPORTIONAL to the SPEED, DRAUGHT (or Pressure) is PROPORTIONAL to the SQUARE of the SPEED, and the POWER is PROPORTIONAL to the CUBE of SPEED.

That is C = k x N, D = k x N^2, and P = k x N^3, where k is a constant for a particular Fan and this vary from Fan to Fan.

Further the VIBRATION will vary as the Square of the Speed, (since the Unbalanced force will increase, to the Square of the Speed) Therefore , increase in the VIBRATION LEVEL (for the increased speed) V2 = V1 x (N2/N1)^2 where V1 is the original permitted Vibration Level, V2 is the New Vibration Level, N2 is the new increased speed, N1 the original speed and it is to be checked for its permissible limits, if exceeds, Dynamic Balancing to be done.

The Capacity cannot be blindly increased as it will over-load the motor. Of course, depending upon the Motor Capacity, the pulley size can be varied.

If you say the Motor can be replaced with a higher H.P Motor, then the shaft strength etc. is to be checked and if need be Bearings are to be replaced to suit the higher RPM of the Fan., and Dynamic Balancing is to be checked as the Vibrations.

DHAYANANDHAN.S

Dear Friend,

Pl.refer my posting No.11. I forgot to add one more point. Treat this as continuation of my Posting No.11.

Pl. measure the current drawn by the motor before you decide to increase the speed, and calculate the KW, drawn by the Motor. Then calculate how much further you can load the motor, this difference will help to decide how much speed we can increase.

Let us say the motor is 100 KW, and initially loaded to 70% and hence further 30 KW can be loaded. Hence the ratio is 100/70 = 1.43 (approx.)

Now the Speed increase required for full getting the full load = (N2/N1)^3 = 1.43. You know the original speed N1, hence N2 can be calculated.

As a result, the capacity increase is N2/N1, Draught increase will be (N2/N1)^2, and Power drawn will be 100 KW (as per the example referred above)

DHAYANANDHAN.S

From the original post, "how to re-size the motor pulley or fan pulley to reduce the air qty.".

Simply reduce the flow at the input manifold, like put a piece of cardboard over the intake hole. Adjust size of cardboard to achieve desired flow. When desired flow as achieved, replace the piece of cardboard with a permanent obstruction, like plywood.

Uh, won't that cause cavitation?

So what. Industrial blower motors run like that all the time. If you reduce the flow you reduce the motor load, therefore reducing current draw.

You're no fun.

How does that work?

Not with a centrifugal blower or pump.

A positive displacement pump, yes.

Decrease flow or SG of pumped fluid, decrease work. Increase flow, or SG increase, work.

Look at a pump curve.

I think we are talking air here.

Doesn't matter. The same principle applies.

Right, That's two threads today that I have totally mis-read. I'm distracted every two minutes by having to blow my nose.

Sorry bout that.

But, as Tornado said the fundamentals are the same.

In a blower; if I restrict intake would I not decrease the air density within the blower?

If I restrict airflow at exhaust would I not increase air density within the blower?

Since the air density would be a variable in blower drag would the effects not be opposite in terms of the rotation slip angle, reactance, back EMF, motor current and power consumption of the electric motor?

Ok, I've got my knife and fork out - is it crow again?