How to Determine CFMs of a Leaf Blower?

Hi Twind-Storm,

I don't know what units mpr stands for. I was thinking meters per revolution, but that doesn't sound reasonable.

Anyway, you need to multiply the cross-sectional area of the nozzle by the average velocity at the nozzle, keeping consistent units. Convert that value to CFM and you're done.

Leaf-blower velocities are pretty high, so just a couple of velocity measurements at the nozzle will be close to average.

Best Regards,

Mike

Yes, the cross sectional area of the end of the outlet (in square feet) times the velocity at the outlet (feet/minute) should give you a reasonably accurate measurement of cubic feet per minute. (Remember area equals the diameter squared times pi divided by 4) The actual answer will be slightly less since the actual hydraulic diameter of the air exiting the end of the leaf blower is slightly less than the physical diameter due to orifice and boundry layer effects. Probably negligable considering the accuracy of your velicity measurement.

Now if you are trying to inflate something with air using your leaf blower, figure that your measured CFM number will decrease as the back pressure increases.

If my nozzle end is 2 1/4" round and I have 180 miles per hour air speed what is the CFM then? I am not sure how to figure the square feet of nozzle end.

I am a landscaper and not up on my math skills sorry for my lack in math.

Thank you again for your help

Thank you for your reply

mpr stands for miles per hour

I have a 2 1/4" round discharge opening and the impeller is rotating at 6000 rpm's

and air speed of 180 mph.

what is the cross sectional measurement?

what would my CFM's be then?

Thank you in advance

Twind-Storm

CFM = 5239.8

With 2.25" round discharge port and 180 mph wind speed or velocity

Is that 523.98 cfm?

Thanks for your time and assistance.

Twind-Storm

With round discharge port being 2.25" and air velocity of 180 miles per hour

I came up with 550 cfm is this accurate?

Thanks again for all who assisted with my need to know.

Twind-Storm

ABOUT 525 CFM

With all due respect... If the math works out to 437 cfm, how can some say 525 cfm???

WITH ALL DUE RESPECT, THE MATH IS NOT STRAIGHT FORWARD. THERE IS TURBULENCE NEXT TO THE PIPE SURFACE AND ALL THIS WAS TAKEN INTO ACOUNT WHEN ENGINEERS DESIGNE DUCTULATORS ( CALCULATORS USED IN AIR MOVEMENT DESIGN). THE DUCTULATOR PROVES ACCURATE WHEN TESTED WITH A MANOMETER AND BALOMETER SO I TRUST WHAT THOSE THAT WENT BEFORE ME IS CORRECT IN THIS MATTER

So the math works out to 437 cfm correct?

I am trying to reach 500-550 cfm

1. How can I increase the CFM ?

I am using a 79cc 4 stroke engine(mixed gas and oil) off a shindaiwa Backpack blower for my proto-type the engine alone weighs 10.5 lbs

2.Is there a engine with more power or speed without weight increase?

Thank you all

Twind-Storm

We are talking about a landscaper trying to design a hot shot leaf blower not some fancy air ventilation system. The additional cfm sucked into the exit air stream through turbulence does not come free, nor can it be defined as an absolute quantity in the case of a leaf blower being used as a leaf blower. My take is that this gent just wants more blowing power and wants to know how to get it. In this case, provided that he has the oil/gas mixed at the optimum ratio and the fuel/air mixture adjusted properly for that engine and still can't get it to turn faster than 6100 rpm his only choice is to go to another engine offering more power either through increased rpm turning the same blower wheel or larger displacement turning a larger wheel at similar rpm. We can even get into designing a venturi at the end of the blower pipe and all kinds of interesting stuff but, I don't think this gent is trying to design and manufacture the next super leaf blower that we all must have.

With all due respect TwindStorm is more than a Hot Shot Idea. I am a simple Landscaper that God entrusted stewardship for a New design and I have been working with due diligence for over 10 yrs on redesigning the Backpack blower.I have created two working proto-types and I am currently blowing 180 mph out two seperate discharge tubes and I am sincerly looking for any and all suggestions that will help optimize TwindStorm so that I can hopefully have It manufactured and Sold Globally .

I do not have a engineering back ground yet Through 28 yrs in the field I know that TwindStorm expidites the job of blowing in less time with less man power and effort with greater control. I have climbed up and over many hurrdles and only have a few things that need tweeked or fine tuned.

My previous questions are real and would be benificial if I can solve some of these questions.

Sincere Thanks in advance

TwindStorm

Hallo Twind-Storm,

As Conwaytech stated, the calculation of 437 cfm is purely theoretical.

The actual cfm might be more like 400 cfm to perhaps a bit more. You are asking to get 500 to 550 cfm, that is a big spread, I think.

Roughly speaking, you are looking for 25% more air (400 to 500 cfm). That would not be possible with the same engine. You might squeeze a few % but not 25.

What make engine is it you are using? If you like you may contact me off list at: ropex at rogers dot com. Rolf

PS: I am wondering why the second correct answer was raised from 1 point to 2 points to now 3 points??? Did he complain???

Your Email bounces, Rolf

Rather than starting a new topic, I was wondering if anyone knew the typical specifications for the motors used in an electric leaf blower?

I'm trying to design a leaf blower for a school project, and I'm not sure how motor rpm will translate to airspeed and cfm. I know that the rpm and power of the engine both matter, but I'm not sure exactly how. Any advice/knowledge would really be helpful.

I am willing to be wrong in my answer,but I know what it is like to work through a project with limited background in the technical department.

The power of the engine source determines your maximum RPM's which relate to the air speed in the fact that they (RPM's)regulate the speed of the impeller which in turn determines the air speed which then gives you the ability to figure the CFM's,by using the formulas above.

I have simplified the formula if you need a layman's version.

Your air speed is measured by a couple different devises. 4. is my suggestion to save money.

1.A Pitot tube hooked to a Air speed indicator.(aircraftspruce.com)

2.A type of cup wind vane that is read by a digital mph devise.(maximum products)

3.Anemometer LOOK FOR ON THE WEB

4.If you have a small local airport go in and ask if someone will let you test the air speed on a Pitot tube on one of the aircrafts.I did this and they happily assisted me.

Hope this is accurate and helpful for your project.

Fellow student in the art of ingenuity

Thanks a lot for the fast response. Once I have chosen a motor this will be very helpful and will save a lot of time! I suppose that is where I am stuck. I know what I would LIKE my cfm and airspeed to be, around 250cfm and 190mph..nothing too spectacular, but I just am a little unsure how to pick a suitable motor and impeller.

I know that many electric blowers use a 12amp motor, but it seems like there is such a huge range of watts and rpm that the engines use that I don't know what to look for. Specifically I would like to use a DC motor for the leaf blower, but I suppose I could choose AC.

I actually even thought that I could use a boat bilge blower, or several, to generate the airflow. But all I can find out is that they move air at around 225cm, but I couldn't find anything about the airspeed they generate. I suppose calling a boating supply store and taking a trip to home depot to ask about leaf blower engines may be in order!

Try going to a few local lawn mower shops and ask them if they have any impellers and housings or trashed hand held blowers gas or electric that you can have for your school project.

Then you would only have to retro fit the motor shaft to the existing parts.

God's speed in your endeavor.

If you need to talk over the phone about your process contact me

@ cliffpeters@iol14.com