Snowblower Snowblower impeller/auger speed question

[RedDirt]

What is a typical speed for a snowblower impeller? Auger? Impeller:auger ratio? I have web searched and searched and mostly find the speeds not listed in mfg specs and in other sources just too much info that does not apply to my specific needs.

Here's what's up. Yesterday I purchased a 46" "garden tractor" snowblower for $250 (a great deal...I think) and I want to convert it to run off my bx23 pto. There are no make/model numbers on the unit but it would seem to be similar to a Berco, more or less. Owner says he purchased from Orchard supply (now Sears?) ten years ago to run on his Kubota scut pto but never got to it, moved to a lower elevation and now moving again and he is "lightening up". The machine has never been used, original paint without a scuff on it but faded for living ouside a number of years, still turns over freely but seems a tad bit stiff. I suspect some disassembly, clean up and fresh lube change will improve that. Alas, no manual.

Here's a couple of photos.



MY unit has a 12" dia four blade impeller and a 16" dia auger. The impeller to auger ratio is 10:1 impeller:auger.

Here are a few example specs:
Kubota B2781 rear 50" 17.5 dia impeller rpm not given, 14" dia auger 286rpm
Kubota BX2750C front 10" 16" dia impeller 903rpm, 12.8" dia auger rpm not given
Puma 48" rear, 20" dia impeller 540rpm, 16" auger rpm not given
Berco snowblowers - impeller/auger dia and rpm's not given

With my smaller impeller (12"dia) and 10:1 impeller:auger ratio I am thinking I need to run faster than any of the above, something like 1000 - 1500 impeller rpm w/ 100 - 150 rpm auger speed. Too fast? Maybe it should run even faster.

If anyone has the missing specs for the examples above that may help. If anyone has a blower similar to mine (or similar specs) that would really help. If anyone has any general observations/comments regarding impeller/auger speeds that would be most appreciated.

Bottom line is I am looking for informed suggestions regarding what speed I should run my impeller.

Thanks - Ray

 

[RedDirt]

If my particular snow situation affects impeller speed here is "normal".

We get low elevation Sierra snow commonly known as "Sierra Cement" because it is usually pretty wet. It begins to snow here at around 34 degrees and we rarely get into the teens. Normal night temps are 22-36. Every 8-10 years we get to zero but it only lasts a week or so.

Normal snowfall is just a dusting to 6-8". Oftentimes big, fat, quarter (25cents) sized, flakes. A fun snow is the fifty cent variety. I normally don't bother to plow unless there is over 4". A "big" snow accumulation on the ground is 18". Snow can be dampish/dry to very wet. The latter, left on the ground a relatively short time, can be surely labeled slush. If it is snowing heavily I can usually stay on top of plowing before it turns to slush. Powder is rare at this elevation.

I've only had the bx for two winters and I have been using a rear blade with gauge wheels. This normally works fine and I expect I'll continue to mostly blade since a regular storm does not drop enough to warrant firring up the blower. When I get the blower modified I'll just swap with the blade this winter and if it works good I'll build a front blade next year. Then I'll have the hydraulic angle front blade for most of the clearing, and, in bigger snowfalls, push the snow from the edges to center then blow the windrow. At least that's the plan. I won't know for sure until I see how far the blower throws.

Driveway is graveled so I intend to use high gauge wheels or skids on both the plow and blower. The gauge wheels have worked great on the rear blade. They are the extended type for road grading not the short ones attached to the back of the blade. Last year the only gravel I grabbed was a little bit with the front bucket making more space to plow.

 

[Willl]

I don't do snow blowers but I believe the impellers spin the same as the PTO input speed, 540 RPM.

 

[RedDirt]

I don't do snow blowers but I believe the impellers spin the same as the PTO input speed, 540 RPM.

That seems to be the case for the Puma example above but apparently others are geared-up like the one Kubota example.

 

[Adrian Dang]

pronovost snow blower :impeller 540PRM,and there are a gear box behind,the chian for the auger is 50. not have the auger prm yet. but i think it is near the 10:1 too.

 

[RedDirt]

So I"m reading old TNB posts. Impeller speeds seem to be all about tip velocity. From several examples common tip velocities seem to be between 3000 and 4000 ft/min. For these velocities my 12" dia impeller should be run between 955 and 1273 rmp. Seem right?

This would have a fairly slow auger speed with my 1:10 ratio impeller:auger. My auger flighting is 3" wide whereas I see some specs w/ 1 1/4" and 1 1/2" flighting. Maybe the wider 3" flighting can be run slower? Seems reasonable. Might even run better on our wet snow than thinner flighting turning faster(?).

 

[ChuckinNH]

Perhaps you could look under a few new lawn tractors, and see what size the drive pulleys are there. You have a drive pulley on the blower probably so you could get some kind of ratio. I would think that blowers are run at max rpm like mower decks. Just a thought.

 

[charlz]

Well you have 3 factors right? Impeller speed, auger speed and ground speed. I would think the engineering between impeller and auger speed has already been done. If the augers feed more snow then the impeller can expel you will simply start 'pushing' snow. This is where your ground speed comes in... if you start pushing snow, slow down HST gives you a big advantage here as you can slow down without affecting your pto speed... not so on my old gear tractor

I guess the real question on impeller speed is what the gear box can handle. The faster you spin it the further it will throw and likely the faster you can go ground speed wise.

My old Kubota b2551 pto shaft is straight to the auger gear box. I have played around (we don't get enough snow to call it 'work') with the different PTO speeds 540/800/1000 and throwing distance is the only real difference. My manual says to run it as fast as possible... not sure what that really means... PTO speed? engine RPM? No doubt my blower is old and tired and probably doesn't throw as far as it should but I find 540 works just fine as I don't need to move the snow very far.

 

[RedDirt]

That's a good idea Chuck to check out an existing lawnmower pulley. My Wards tractor has a mower deck but it runs from a front electric clutch pulley not a vertical drive pulley below the motor, the way this blower was designed to operate. I intend to check my clutch pulley rpm but I haven't yet had the chance. That's likely my best chance as town is an hour away and I don't go often. I agree the blower is probably meant to run at full throttle. The blower has a 1:0.6 reduction gearbox on it to slow down the impeller some. If the engine speed was 2500 rpm that would still have the impeller running 1500 which seems high so there is probably a pulley reduction before the gearbox.

You are right Charlz in that the impeller:auger ratio is already engineered. I'm not sure what the gear box will handle but it's fairly beefey. The drive is double chain and sprocket in a housing. Big gear is 19 tooth on a 1 1/4 shaft but has bronze bushings. Small pulley is 11 tooth on a bearing mounted 1 1/8" shaft. Auger box is a shaft driven off the center of the impeller and is a worm and gear assembly. This is bushed too but here rpms are quite small. The bushed big gear in the main box is probably my speed limiting factor.

But I may do away with the primary box altogether. It is a reduction box and I need to increase speed. But then again, I have a 4:1 gear box that may work to increase pto then I'd reduce with a pulley to the main blower box to get the right impeller speed. There is a lot of mechanical losses in this set up but I've got the important parts in hand and I think I have pto power to spare. I may check ebay for an appropriate box.

And a buddy/mechanical mentor is coming Thursday to give me some feedback. His bag is hydraulics and has a bunch of stuff in his bone yard so we could go that way too. In short, drive train is yet to be determined.

I tore down the blower today, cleaned both boxes and re-greased. What used to take a firm grasp on the pulley to rotate the impeller can now be done with one finger!

And while down I could get an accurate measurement of the impeller. What I first thought was a 12" diameter impeller (measured with poor lighting and reaching back into the housing) turns out to be 14". So I'm now looking at about a 900rpm impeller speed that will give me almost 3300ft/min tip velocity. I don't need 5000ft/min to throw 100ft as someone else posted elsewhere on tbn.

Still looking for an informed opinion if my target impeller tip velocity of 3000 - 4 000 ft/min is close to correct.

 

[rbargeron]

.......still looking for an informed opinion if my target impeller tip velocity of 3000 - 4 000 ft/min is close to correct.

Based on a 3pt hitch single-stage direct drive snow thrower I once had, 3k -4k ft/min tip speed is on the slow side. Dry snow will fly 20-25 feet but wet slushy stuff will fall 8 or 10 feet away. That may be enough unless you are clearing a double-width driveway area. I found that a tip speed up around 4500 did a good job under most conditions. There's some talk of tip speed scattered in this thread about adding a 2nd pto speed to my tractor.

 

[RedDirt]

Thanks rbargeron, your reply and especially your linked post was quite helpful. I think I am going to up my target velocity a bit and try for at least 4000, maybe 4200ft/min. This would put my impeller rpm around 1000, 1200. If my mod works I think the unit can handle the increased rpm's.

My buddy's coming by tomorrow and I am anxious for his input. He was my equipment fabrication instructor in college thirty + years ago so I value his opinion. If he steers my to hydraulics I'm likely to have to ask a bunch more questions. Not only do I need to increase speed I need to reverse direction and this is a challenge mechanically (on a budget!) which is why hydraulic may be easier.

Will keep you posted.

 

[rbargeron]

.............. I need to reverse direction and this is a challenge mechanically.......

Yes - I noticed the chute was on the opposite side from most machines. In past years Bervac made an interesting adapter for putting a rear-mount up front - they used an extra sprocket to change pto direction. There would be some opportunity to change speed with sprocket sizes. pics below. Erskine's chain box is enclosed running in oil. But for homeowner use an exposed setup might hold up well enough.

 

[RedDirt]

they used an extra sprocket to change pto direction.

Boy, would that be a handy item for me to have right now. Anyone got one to let go?

I have searched for a suitable gear box on the web and come up empty. Lots of boxes available, especially right angle ones, but parallel shaft in the 2:1 range are not to be found. Anyone know a source?

I had a better reply written then accidentally closed the page before sending. Hate it when that happens. Here's the condensed version.

Buddy came and we brainstormed a pulley/belt solution. Seemed better than my chain/sprocket. Hours of struggling to get it developed on CAD just led to the conclusion it would not work. Too many twists in confined spaces. Belt would have jumped the sprockets. I'm now reviving a previously dicarded concept using spur gears. The design came out well and the plan is off to Owen for look-see-comment.

I had to sacrifice 200 rpm from the belt design to keep cost comparable and keep the conversion package within the confines of the blower body. If I use the bigger gears material cost goes up 40% and the gears need more complicated support. I should get 1080 rpm, 4000ft/min impeller tip velocity. Hope that is enough. I don't need to throw but about 10' -15', 20' - 25' would be a bonus. Too bad wet snow is what we normally get.

I'm also having trouble finding a web source for American gears. Found a great metric gear place, Quality Transmission Components, qtcgears.com compleate with detailed measurements and cad drawings of thousands of gears. But no one like it for fractional gears. Owen is a quality machinist so we will bore out metric gears if we need to but finding the right bores in the first place could save that step. Anyone know a source?

 

[RedDirt]

Here is my current plan if anyone is interested. I value all comments and advice.

My main concern with this design is if the 3" impeller gear is too small. I had larger pulley and a larger sprocket on those designs but I think a solid gear can be smaller. A 1" bigger gear here means a 2" bigger gear above, etc, and the whole assembly gets much larger and likely cost prohibitive.

View attachment Snowblower Gear Drive_112009.pdf

This is a 24x36 drawing so it is only viewable onscreen unless you have a plotter. Also it is is a see-through drawing. You may need to compare the two views to see what overlaps what. For me This type of drawing works to find conflicts. If it was a published drawing I'd hide appropriate lines/layers and add additional sections so there was no overlap of details in depth.

 

[PILOON]

Reddirt:
I sent you a PM

 

[RedDirt]

Reddirt:
I sent you a PM

Thanks PILOON, I've replied.

--------------

BTW the reason I'm using 1 1/4" shafting in the pdf drawing is that 1 1/4" is the existing shaft from the blower (with a 7/8" dia spline tooth end that goes into the back of the impeller fan). This shaft went into a gear reducer box that I am discarding except for the shaft. The big gear jack shaft is 1 1/4" because Surplus Center has a neat and reasonable 15hp pto shaft that ends with a 1 1/4" bore where I can connect with a shear pin.

 

[ChuckinNH]

I picked up a brochure on the Frontier 3pt hitch snow blowers today, and it has this information about impeller / auger speed.

Tractor PTO speed: 540 rpm
Auger speed : 170 rpm
Impeller Speed : 540 rpm

This information is for the smaller ( up to 74" blowers)

 

[RedDirt]

Tractor PTO speed: 540 rpm
Auger speed : 170 rpm
Impeller Speed : 540 rpm

Nice to see another slow impeller speed. Most of the specs I found give higher auger speeds. As far as impeller speeds I think tip velocity seems to be the critical issue and that depends on both the rpm and impeller diameter.

I did find a web source for American gears but I cannot yet comment on pricing as I have to wait for a quote. But their website has a good online catalog and dwg drawings and also a pdf downloadable catalog. What I really liked was their online HP formula calculator. Once I figured out gear terminology I could change variables and compare one gear choice to the next. Gear material, Dia, pitch angle, tooth count, gear thickness, rpm, service factors, etc are the variables and the tool instantly calculates the HP, velocity, torque, pitch loading, etc. It was easy to see which gear would perform better. I was lucky with my uninformed gut reaction choice and had happened to pick very suitable gears for my project. The calculator answered comparative questions like more teeth better or not but more importantly confirmed my gears aren't going to fly apart on the first trial run after putting in a lot of fabrication hours. I can rest a bit easier. The site is rushgears.com.

 

[JohninCT]

This place has parellel shaft gear drives similar to what you're building. I don't know how much they cost, but it may save you time/effort buying vs fabricating.

Hub City Inc - Standard Products

 

[RedDirt]

This place has parellel shaft gear drives similar to what you're building. I don't know how much they cost, but it may save you time/effort buying vs fabricating.

Hub City Inc - Standard Products

Whoopie! I had searched for parallel shaft gearboxes but could not find any the fir my purpose. Thank you. First glance at Hub City's catalog and specs indicate they may have a suitable reduction box. I got a quote for a "think it may work" gearbox from my local distributor and it is $600...almost triple my homemade reduction assembly. But the distributor just happened to have four new "surplus" boxes exactly the same that he would sell for $400ea. So now that's got me thinking again and back to deciphering specifications. By the time I add supporting steel to my gear, jackshaft and bearing assembly the $400 may be about a wash.

In the meantime I received the gear quote from Rush Gears. You can go to their site for the good design tools and drawings but buying there is out of the question for a single gear. The 6" gear I need was $1600 for one or $350 for 10! I found a similar gear at McMaster & Carr for $136. Unfortunately Mc does not carry the heavier duty 20 degree pitch angle gear, only the 14.5PA type. A trip to rushgear.com HP tool calculator says the 14.5 gear just meets my HP needs.