Squirrel cage blower rpm. Check my math.

[Ron_J]

So i just picked up a used blower and it doesnt seem to put out the air that i think it should.

It is a 12" wheel (with no markings or labels) and from what i can tell, 1550rpm is pretty standard for that size.

It has a 1/6hp, 1725 rpm motor on it. A 2 1/2" pully on the motor and 8" on the wheel.

I figered a reduction of .3125. So that means the wheel is making about 540 rpm.

1725 seems to be typical for an electric motor. But the 540 appears to be pretty slow.

Am i missing something?

 

[Bert_]

So i just picked up a used blower and it doesnt seem to put out the air that i think it should.

It is a 12" wheel (with no markings or labels) and from what i can tell, 1550rpm is pretty standard for that size.

It has a 1/6hp, 1725 rpm motor on it. A 2 1/2" pully on the motor and 8" on the wheel.

I figered a reduction of .3125. So that means the wheel is making about 540 rpm.

1725 seems to be typical for an electric motor. But the 540 appears to be pretty slow.

Am i missing something?

1/6 hp isn't going to move a ton of air. You can speed up the blower but will probably need more motor.

 

[Ron_J]

1/6 hp isn't going to move a ton of air. You can speed up the blower but will probably need more motor.

I'm not sure i understand this statement...not saying that you're wrong.

I would think that the rpm of the motor would dictate the amount of air you move. Assuming the motor has enough hp to turn the wheel at the rpm that the motor is rated for.

Matbe the motor isn't reaching the max rpm, but it isn't overheating.

 

[Bert_]

I'm not sure i understand this statement...not saying that you're wrong.

I would think that the rpm of the motor would dictate the amount of air you move. Assuming the motor has enough hp to turn the wheel at the rpm that the motor is rated for.

Matbe the motor isn't reaching the max rpm, but it isn't overheating.

You can change the pulley but it's going to overheat the motor. These would have not had much more hp than required.

The pulleys are set up to work with that 1/6 hp motor. Whatever the original application was it didn't need a lot of airflow. So they ran the blower at a low speed with a small motor.

Easiest way to see how loaded the motor is with an amp meter. You don't want it to pull more amps than it says at the motor.

 

[Renegade1LI]

The best way to check rpm is with a tach, I check all my equipment with this to get a true speed. It's great for double checking vfd output.

 

[karoc]

On the open side of the blower take piece of cardboard and cover the opening. Some of those blower section motors are two/three speed

 

[Leaflessshadetree]

How much air is it putting out?
How much do you think it should put out?

Is it just sitting in the open or is it enclosed and attached to something (duct work)?

 

[Ron_J]

How much air is it putting out?
How much do you think it should put out?

Is it just sitting in the open or is it enclosed and attached to something (duct work)?

It is just sitting in the ope at the moment. I know it will blow more with a little restriction. I am just comparing it to what my 8" does sitting in the open. Just seems like it doesnt blow any more than the 8".

I will be builda housing for it shortly, but wanted to make sure it is turning the correct rpm before i did.

Like i said, i picked it up used and I'm pretty sure the motor on it isn't the original.

 

[nbpt100]

You math is fine but it seems like you need to back into what you need for a blower. What SCFM do you want or need for air flow.? From there you can determine if you have an appropriate motor and reduction.

 

[TRWham]

How do you know how much air it is moving?