Snowblower Snowblowers - Long chute or Short chute ?

[TMcD_in_MI]

</font><font color="blue" class="small">( And, the snow will exit at the impeller input speed ...or, it would back up in the chute.)</font>

Joel, you sound like someone with some knowledge of physics, but it seems to me that your statement isn't true. I agree that it would be true if the snow were a non-compressible fluid, but wouldn't the snow stream be better characterized as a gas and solid particle mixture? Given that, it seems that the stream could, in fact, slow down a bit at the chute exit, resulting in a density gradient inside the chute that increased in the direction of the exit. i.e., the particles would be closer together at the exit end. I don't know of any principle that would require the particle speed to stay constant.

What *would* have to stay constant is the mass flow rate. If 2 kg/s of snow are coming from the impeller, then 2 kg/s have to exit the tube, or, as you said, it will clog up. At the exit, the snow particles are going a little slower, but they are packed more closely together, so the mass exiting the chute each second will equal the mass entering it each second.

So, it seems to me that the longer the chute, the more the snow will decelerate within it, due to gravity and friction. And this would lead to more chance of clogging in the long chute as Mr. Skurka has observed.

Hope this has made sense.

Tom

 

[JoeL4330]

I agree with everyone ...theory fails at some point; perhaps we need a "chute-out"

 

[rambler]

</font><font color="blue" class="small">( </font><font color="blueclass=small">( Large impellers for slow pto speeds, smaller impellers for fast pto speeds.)</font>

Paul, not trying to argue, but I've never seen that. So that leads me to a question. Are you saying that a smaller impeller fan is used at 1000pto speed and a larger one is used at the more tradiational 540pto speed?

The impeller fans I measured out were all within a few inches of each other, the smaller units having fans of about 18" to 22" and the larger units having fans of roughly 20" to 24". It seemed to vary more by brand than anything else. For example: "Brand X" would use 18" fans in their smaller blowers and 22" fans in their larger blowers, but Brand Y used 20" and 24" fans respecitively.

Here is a whole thread about a long chute blower that simply couldn't blow wet snow. It simply clogged the chute. It looks to be the very same blower that is in the first picture of this thread. Snowseb's clogging snow blower thread


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There is an optimum fan speed, over which you don't get much increase in snow capacity or throwing distance. I'm used to 8' wide, double cross auger, 2 stage snow blowers. Most have a larger impeller than you mention, and run at 540 rpm. They like 60-120 hp.

My blower is 7', has a single cross auger, & a smaller impeller, more like your size.

Then there are the 150-200 hp blowers, might have triple cross auger, run at 1000 rpm, and likely have a huge fan for capacity.

What we are not figuring is the impeller design, number of blades on it, shape, etc. /forums/images/graemlins/smile.gif This will all need to match - impeller size, rpm speed, number of blades, shape of blades. You can design most any of the options to work out with the available differences.....

Most important for moving the snow is the impeller clearance to the shroud, as i mentioned before.

Beyong that, the transition from the tip of the impeller to the chute is very important. Some like to choke down the snow with a poor design, or transition. Some go from the square impeller blade, to a round hole, and back to a square chute - or some other silly design. This has a big impact on the plugging of a snowblower.

Next, the chute design itself. A true square chute, with the one side (bottom of curve) totally not there is best. Some have that 4th side filled in at the bottom, part way up. This will really plug up under some conditions. If the snow, for any reason, slows down & falls back, it needs a totally open (bottom) side of the chute, so it can get out of the way, fall out easily. As well the air has some place to exit with this open side - totally open - and that helps to keep trouble snow types clearing away. If the air can't get away fast enough, you lose the battle, everything slows down.

Very minor differences in the transition or chute angles can make a huge difference, but not look so terribly noticable to you or I.

As well, a rusty inside, or otherwise rough chute surface will clog up real quick. Often noticable the first time I blow snow for the season.

Wet snow will clog up. Dry, cold powder will not.

I kinda suspect one of these differences had a lot more to do with a clogging snow blower, rather than a foot or so of difference in the length of the chute. But, that is speculation on my part, and not an argument either. /forums/images/graemlins/smile.gif Enjoying the thread. /forums/images/graemlins/smile.gif

--->Paul

 

[BigEddy]

Call me a skeptic, but I don't buy the tip - body clearance argument.

If I have a 20" auger in a 20 1/8 hole, or a 20" auger in a 22" hole, I still have a 20" auger with the exact same tip speed. The particle of snow on the tip of both augers will be travelling at the same speed as it "leaves" the auger and heads up the (short or long) chute. Therefore that same particle of snow should travel the same distance as its tight cousin does. Sure there will be some snow that is "missed" by the auger and falls back down to be picked up next time around, and there will be some friction losses as the auger repeatedly passes the missed snow - but neither of those would impact the speed of the snow exiting the blower and therefore won't impact distance. If we add the "fan factor" to the equation, the air in the impeller opening is also rotating at the same speed as the impellor itself, and will tend to lift the missed snow up and out the chute along with the pushed snow - at essentially the same speed.
I'm an Engineer - so I could be overlooking the obvious.

 

[rambler]

</font><font color="blue" class="small">(
I'm an Engineer - so I could be overlooking the obvious. )</font>

I'm a simple dirt farmer is all.

At the farm auctions, the snow blowers that are tight & square impeller will bring $1000-1200 all the time.

The blowers with rounded impeller edges, or extra clearance between the impeller & the tinwork go $500. "Oh, wore out, won't throw snow" is the comment as farmer after farmer walk by.

Other visible conditions don't seem to matter much on the pricing.

You should see the difference a slight roll to the edge of a combine platform auger makes on feeding crops into the combine! Or, the difference a little wear or a wrong angle makes on a post hole digger. Same deal here, if you can relate one to the other.

But then, I spend a lot of time with the hammer & torch & grinder fixing the machines into something useable from what the engineers developed..... /forums/images/graemlins/wink.gif Real-world keeps getting in the way of their plans.


Thanks for the chuckle, all I'm doing here. /forums/images/graemlins/smile.gif My best friend is an engineer.
--->Paul

 

[BigEddy]

Now this is why this board is so great. My brain tells me that there is no difference, while conventional wisdom says there is. No amount of figuring will convince me there is a difference - but when Rambler says that farmer after farmer will pass up a "worn-out" blower - then I know that my brain is wrong - there is a difference - and clearance between the impeller and housing is something to look out for. Cause Engineer or not, I'm smart enough to realize that the guy who uses something day in and day out will be the first to understand what seperates the good from the bad (or the wheat from the chaff)
Thanks!

 

[trlong]

Without getting into the auger clearance issues, adimitting my lack of knowledge of the physics, turbulance, gradient, etc....

Could the concept of the taller chute simply be the hope that the snow is more likely to be above snowbank height when it leaves the chute, thereby reducing the necessity/frequency of having to blow the snow high where the wind can more easily catch it? Just a thought.

Ofcourse, the above would assume a relatively flat deflector angle, which would increase clogging with wet snow. IMHO.

Tom

 

[Bob_Skurka]

</font><font color="blue" class="small">(
Could the concept of the taller chute simply be the hope that the snow is more likely to be above snowbank height when it leaves the chute, thereby reducing the necessity/frequency of having to blow the snow high where the wind can more easily catch it? )</font>

Depending on the type of snow, my short chute snowblower can easily throw snow up onto the roof of my house /forums/images/graemlins/blush.gif

 

[trlong]

Bob,

Was just a guess as to a simple explanation, on my part. And, yes, my short chute will send dry snow into a 50' high plume. However, the less high I throw it, the less the wind catches it and turns me into a snowman. When the snow gets deep and I have to blow snow higher, and higher, I wonder if a taller chute with a low deflection angel would help with the wind driven blowback? Ofcourse, if I had a cab..... /forums/images/graemlins/frown.gif

Tom

 

[hwp]

It seems to me that there may be one important variable that has not been included in the discussion so far, i.e. the amount of snow that is being handled. My observation is that my snowblower throws snow much further if it is working close to capacity compared to a minimal amount of snow under the same conditions. I'm not inclined at the moment to work through the fluid dynamics involved but my guess (as a one-time engineer) is that under minimal snow loads the snow particles are discharged somewhat independently primarily subjected to friction and gravity. But under high load conditions there may be a bit of a push phenomenon so the snow particles cannot slow down as much and therefore there is a greater discharge velocity leading to a longer throw. If there is any merit to the "push" theory, this might explain why the clearance between the impeller blades and the drum is so important. Or it might not. Regardless of the theories presented, at the end of the day I prefer a short chute over a long chute and a minimal impeller gap to a wide gap. /forums/images/graemlins/smile.gif