What is the best rpms for blowers?

It has been a long time since I have owned and operated a truckmount. I have
been using Cross-American Recoils and Jaguars with 2HT propane heaters since
the last 1990s.  I now have ordered  an EZ 18HP Vanguard with a 36 blower
from Nick Nellos. His setup is similar to a brand I used to sell Steamaction in that
they both use the oridginal throttle to operate the machine. My Steamactions were
direct coupled and the new EZs are belt driven but the pulley ratio is one to one.
So the engine speed is the same as the blower speed.  Back in the 1980s and 1990s
almost all truckmounts either had the throttle independent of the engine so as to
keep the rpms at their recommended speed. Most ran at 3000 . I am reffering to
truckmounts with 3L/36s ,4M/45s, 4L /47s. Back then the maximum for most blowers
was recommended at 3050-3275rpms or less as best I can remember. Now the ones I am reffering to all have a maximum rating of 3600 rpms. Also for some of the blowers the vacuum pressure allowed is higher. For instance the 3L/36 used to have
a max of 12HG recommendation.
So for you truckmount guys I am just asking what are you doing? If is safe to run these blowers at higher rpms then that could be a good thing providing more cfms.
Another thing is it better for air cooled engines to run at 3600 rpm than like 3000 rpms?

Lots of questions...good ones actually. Not sure if there is a universal answer independent of the machine. I've always seen 36 blowers get spun faster than others, but I think it all depends on the machine.

I'm sure Odin or ACE will be along to shine light on this...I just run them, I don't build them.

My blower is direct coupled to the engine and the manufacturer recommends 3200-3300 rpm. My blower is a Tuthill 4007. You can go to the manufactures website of who makes your blower and they should list that info.

The slower they run the longer they will the last and the quieter it will be. However you get reduced performance. The manufacturing company of your blower will have performance charts that will determine those numbers. The maximum rpm for most blowers is 3600. Higher end units like Gardner Denver will have a max of 4000 rpm. How ur machine runs will be up to you. The more hp you have to work with the faster u can run it. I have heard of people who over drive them and use water to cool them.

Thank you all for such good answers to my questions. My first truckmount was a Prochem CubXL and I remember that the engine and the blower were setup to run at 3275 rpms. That was a long time ago. You probably remember that it used a 16HP Vtwin with a Sutorbilt 3M. When I started looking for a truckmount I could have purchaced  from Nick a
EZ 16HP V twin Vanguard with a 33 Roots . In fact I went down to Wichitah Falls Texas where he lives with that intention. When I got down there however I remembered how much more air flow and just overall vacuum my 2nd truckmount had which was a Prochem Legend. Back then it came with an 18HP Kohler turning a Sutorbilt 3LVL blower. The difference was great. I one time put 350 feet of vacuum hose on my Legend when cleaning the carpet in a Target store. It did that with relative ease which was something the CubXL could not have done without taking numerous vacuum passes. In fact I only had 250 feet of vacuum hose   when I was had the Cub.
More heat as well. Nick made me a great deal for an 18HP Vanguard / 36 Roots blower.  I remember that the Legend Prochem had it set to where it ran at
3050 rpms. 250 CFM@12HG. To be honest for a single wand setup I think that is plenty of vacuum. I suppose I could run it faster when the need for more vacuum and heat. If I can maintain 190 at the truck I feel in most cases it is enough. I believe if I turned it up to 3400-3500 it would give me an additional 20 degrees or so.  
I have one more question. Are air cooled engines typically supposed to run at 3600 rpms? I never ran any of mine that fast but I was thinking that they may run cooler with the additional air flow created by the fan built inside the engine. On the otherhand I suppose running it slower creates less engine heat in the first place.

You can overdrive it a little if needed. They set the specs to cover their rear while under warranty. I have overdriven mine will no bad effects.
Direct coupled an air cooled engine is designed to run 3600 rpms and so is the blower until you reach a #5. Not sure about a #47 but I bet it could tolerate it with no ill effects.
The increase in vacuum from 2800 rpms to 3600 rpms is tremendous and well worth it in my opinion.
If it's choked down by restrictions in the inlet and exhaust then open it up and let it breathe and re- jet your wand to keep up with the flow and temp desired.

When I have talked with kohler engineers they said they are designed to run at 3200 to 3600 under periodic heavy load conditions. Which is what we as carpet cleaners do. This is for the speed of the fan to keep it cool as well as to keep up with hp demands. The hp rating on your motor is assuming a speed of 3600. Anything slower and you get less hp on a sliding scale. I have run all of mine at 3400_3600 at all times with no problems and thousands of hours. Thats what they are made to do. The worst thing you can do to these motors is put them in a metal box with no ventilation. So machines like nicks, judson, tcs etc are not the prettiest girls at the ball but they are using the motors the way they are supposed to be. Out in the open. If you want more life out of your motor go buy a ventilation system to blow that hot air out from behind your motor. I use a transmission cooling fan from autozone, pointed right out the back door. Dropped the inside van temp by 80 degrees.

I'd say the short answer as for blower RPM, would be to run it at the manufactures rated RPM that produces the Max CFM.

From the reading and research I've done it seems like that max RPM varies quite a bit from one manufacture and blower size to another. So like someone else already suggested, find the specs or manual .pdf file online for the blower you have.

I did just that awhile back for my Roots 36, in a quest to improve CFM and found the CFM to be much higher when I tested it spinning it at it's max, 3600, and compared to the way it was setup and I've been running it for many years, 3000 RPM. Being my blower is direct drive via flex-coupler to my engine, it was setup to run 3k RPM's because that's what was good for the 20hp Onan I had.

When I recently replaced my Onan eng with a new 25hp Kohler, I had intentions of running it at 3600 RPM to get the added CFM. Since the Kohler's "max RPM" is 3600, and that's where it produces peak HP I figured it was the plan.

BUT, when I got the K eng in and running, I soon realized and it occurred to me, running it at max 3600 RPM for sustained periods of time was not going to be a good idea if I wanted it to last........I ran it for about 2 min @ 3600 to test the CFM, and I couldn't run back to the machine fast enough to turn it down, in fear of it hand-grenading.
Once you get those little eng up to about 3400 RPM and beyond they're just absolutely screaming, and for me it became pretty apparent I'd better stick to 3-3200 RPM to be safe.   

I really think the "max RPM" for theses small engines is no different than the max RPM (Redline) in your car, or really any other eng for that matter. Sure you can rev your car that high, and that's where it makes the max HP, but it's certainly not made to run down the freeway for hours running at Redline.

Again thanks to all for all your informative posts.
I really like this forum. So much better than a bigger one I know of. No BS here! This forum should be a great source for serious carpet cleaners ..

Good to have you aboard Jan. Alot of guys here have built and refurbished their own machines. So stick around and join the revolution.

Fuzz, what size in Inches is the fan you added, and what CFM is it, that are you using for van?

I've been planning to add one to the back of my van for the same reason.......I actually just put a 7" 2300 CFM one on the side of my TM for cooling.

Fuzzsucker wrote:When I have talked with kohler engineers they said they are designed to run at 3200 to 3600 under periodic heavy load conditions. Which is what we as carpet cleaners do.............................

If I could get Consistent higher CFM by only running my eng at "periodic" higher RPM's I would do it, but since I frequently run mine for hours at a time on a lot of jobs, it's way beyond what I could consider "periodic"............so help me out here, what I'm I missing?  I doubt you could be doing most jobs in just a few min, or what could be described as "periodic", but maybe some of you are really that fast?...or I'm I just that slow!      

No, what I mean is the machine goes under load. Like when you have your wand on the carpet the motor works harder. Then u pick it up and the motor speeds up from the lack of vacuum pressure. Periodic load. Consistent load would be if the motor was running a drilling rig or something always using the same hp.

just run it the way it comes to you and don't worry about all the numbers and stuff

It would seem horsepower to load ratio  would have to be a factor in considering rpms. I wonder if it would be better for instance to use a 20 horsepower engine using a larger sheave or pulley and running the engine at 3000 rpms and turning a 36 blower@3400 rpms. Also where the pressure relief valve is set could be a factor as well. Of course heatexchangers must be efficient and capable of providing sufficient heated solutions . It seems it's all a sort of balancing thing in order to get the best performance vacuumwise as well as the engine at moderately high rpms and still get plenty of hot water . I use to have a White Magic that had a 24 horsepower Onan that only ran 2500 rpms. It had no trouble turning the 45 Whispair blower 2900  + rpms
but did not provide as much heat as another White Magic which had a 20HP Kawasaki liquid cooled engine that ran 3000 rpms and 45 blower at the same 2900 + rpms.
This example however is 1990s heatexchanger technology which I would think has improved over the years.

Oh ok, I got ya.

But I doubt K engineers state that running their engines at 3600 RPM for anything more than brief periods, with or without a load is a good idea?.......maybe I'm wrong, but running an eng at redline for hrs on end doesn't seem like a good idea to me?

I'll have to call them Tuesday and see what they say.

3600 is not redline for those motors. Just like on ur car red is 5000+. Like I said I run mine at 3600 for years on end no problem. Got 4000 hours on my last motor and the cylinder pressure was as good as the day I bought it. Same goes for the last two before that. I only replaced it for more hp or a new machine all together. The new owner of that motor is still chugging away at 3600.

Btw I think is a 11inch fan. I dont remember the last time I bought one was a few years ago. They seem to last forever.

Jan Sullins wrote:It would seem horsepower to load ratio  would have to be a factor in considering rpms. I wonder if it would be better for instance to use a 20 horsepower engine using a larger sheave or pulley and running the engine at 3000 rpms and turning a 36 blower@3400 rpms. Also where the pressure relief valve is set could be a factor as well. Of course heatexchangers must be efficient and capable of providing sufficient heated solutions . It seems it's all a sort of balancing thing in order to get the best performance vacuumwise as well as the engine at moderately high rpms and still get plenty of hot water . I use to have a White Magic that had a 24 horsepower Onan that only ran 2500 rpms. It had no trouble turning the 45 Whispair blower 2900  + rpms
but did not provide as much heat as another White Magic which had a 20HP Kawasaki liquid cooled engine that ran 3000 rpms and 45 blower at the same 2900 + rpms.
This example however is 1990s heatexchanger technology which I would think has improved over the years.

This is Exactly what my plan is (what I highlighted in red).  To spin my blower at 3600 RPM while running the K eng at about 2800-3000 RPM.........but easier said than done when your machine like mine and many do, that has the eng and blower shafts inline and are direct coupled, you can't just change the size of a pulley to achieve a difference in RPM's.

I've got a couple ideas on this, from moving the blower over several inches to building a fairly complex pulley and belt system that I could achieve this without having to move the blower.....But I'm not going to take action until I feel like I've come up with the best and easiest way to do it........so I keep looking at pics of other setups for ideas.     Heat for me isn't an issue in this for me, since I use a Propane rather than heat exchangers.

I converted my last unit to belts. Wasn't too bad. Just a thick piece of steel and some rethinking of the plumbing. But depends on the layout of ur unit and size and placement of silencer. Keep in mind overhang load should be kept to a minimum. And more complex belts equals more hp loss.

I like belt drive in most cases because one can
have the engine speed and blower speed and different rpms. I realize we do lose a little efficiency with belt drive as opposed to direct coupled. Not sure it has that much of an effect with gasoline engines. One time I took a 2L Sutorbilt and wanted to get 3600 rpms out of it using a 3600 rpm Marathon
2HP motor. According to  Sutorbilts performance data charts I could that . Could not do it with using belts however. So I direct coupled and it worked just beautifully. Had to get a big silencer .
About 130 cfms with 16 amps. About 40 more that the typical Ametek 3 stage of that time ie.. 1990's
But using gasoline engines it is not so critical. But maybe a couple extra horsepower would be nice if one is going from engine 3000rpm to blower 3400 rpms when before it was 3400 rpms for both blower and engine.

Fuzzsucker wrote:I converted my last unit to belts. Wasn't too bad. Just a thick piece of steel and some rethinking of the plumbing. But depends on the layout of ur unit and size and placement of silencer. Keep in mind overhang load should be kept to a minimum. And more complex belts equals more hp loss.

That's what I have in mind, making a |_| shaped bracket out of heavy ga steal that would hold a double wide pulley. That would enable me to run belt from eng to it and then from it back down to the blower.

Do you happen to have any pics or other info of the ones you converted to belt drive, that I could use for reference?

Oh and also, what do you mean by "overhang load"?.............I don't think I've ever heard that.

No I dont have pics of that. That was an old machine.

Overhang load is the sideways force on the motor or blower shaft. The further the pulley get out on the shaft the greater the overhang load. Which is bad.

Really I would just run that unit at 3400_3600. Call kohler, you will see its fine.