Most all snow blowers are either single-stage or dual-stage. Today, machines advertised as "triple-stage" usually rely on a gimmick to make them sound more impressive. For instance, MTD promotes a so-called triple-stage unit that replaces some of the innermost augur segments inside the snow box with a circular drill-shaped element that is driven directly off the front of the augur gearcasing. The "drill" has not at all proven to be more effective and in fact, reduces the crushing power that comes with traditional augurs. In either case, this really isn't a third stage since it's just part of the first, snow handling stage, which is up front and includes the curled, steel augurs (one on each side of the gearbox). By the way, adding the "drill" on the front of the augur gearbox makes the gearbox more complex by adding an opening on the front of the casing with an extended and exposed impeller rod and mount for the drill. This gearbox becomes a critical (and costly) point of failure, in turn diminishing reliability.
Certain vintage snow blowers manufactured by AMF and Garden Way, prior to being absorbed by MTD, had a third stage located in an extended section at the front top of the snow box. These were sold under various brand names, including Bolens and Troy-Bilt (owned by Garden Way), and Craftsman. The third stage was comprised of small-diameter, full-width augurs mounted on a small axle that was belt-driven off the main augur axle. These small augurs served to break down the top accumulation of deep snow and drop it down to the main augurs for processing. The third stage was designed to do the job commonly performed by drift cutting bars. These triple stage snow blowers added size and mechanical complexity, making them more expensive to build and sell, while offering little benefit over drift cutters. As a result, they were not very popular with buyers and the triple stage design was abandoned.
In a dual-stage snow blower, the augurs are driven off a shaft that comes from the impeller to the gearbox that drives the augurs. This is known as the impeller shaft. The impeller itself is located inside the barrel of the snow blower. The front gear box turns the augurs at a ratio of 1 to 4, meaning that the augur axle, which holds the augurs, turns one revolution for every four rotations of the impeller. The augurs reside in the augur box, often called the snow box, on the front of the machine. The snow crushing by the augurs is called the first stage. The first stage feeds crushed snow into the barrel behind the augur box.
The impeller resides inside the snow blower's middle barrel section directly under the chute. It rotates in a counter-clockwise direction parallel to the back of the barrel and the front of the engine. It is disc-shaped and usually painted black. It has three or four clawed arms that scoop up the crushed snow from the first stage and throw it up through the transition (the hole near the top of the barrel, on which the chute sits) and out the chute. The impeller is simply driven off pulley located behind the barrel and directly attached to the impeller shaft. The pulley is belt-driven by the engine. The impeller's throwing action is referred to as the second stage.
The first diagram at the left shows the flow of snow in a dual-stage snow blower. The second photo shows a typical dual-stage Ariens 824 snow blower. The third photo shows a view looking directly into the front of the Ariens 824. You can see the toothed black augurs up front in each of the two photos. The round, black-painted impeller is visible at the rear of the barrel in the third photo. You can also see light shining down the chute through the transition outlet in the third photo.
Dual-stage snow blowers offer a range of 22 to 36 inches in clearing width, which directly correlates to the inside width of the snow box. Dual-stage snow blowers are more powerful and throw snow, including heavier snow, further than single-stage snow blowers. Virtually all dual-stage snow blowers have traction drive, making them self-propelled. The drive on most machines employs a friction disc to drive the wheels at various speeds. Some high-end snow blowers employed actual transmissions for the traction drive. The drive may have anywhere from 1 to 6 speeds (sometimes called gears), depending on how it is configured. Most now have tires that are deeply cleated (Sno-Hog or X-Trac) to provide excellent snow traction without any chains or studs.
A single-stage snow blower eliminates the second stage. These snow blowers are more compact and have narrow clearing widths between 16 and 22 inches. They use augurs with attached rubber or composition "paddles" that both crush and throw the snow directly out the overhead chute. Hence, the single-stage designation. These have proven to be quite effective for smaller areas like walkways and narrow, short driveways. Single-stage snow blowers rarely have traction drive. They are propelled by pushing the handlebar upward so that the paddles pivot forward and hit the ground to provide some assistance in moving forward only. The downside is that using the augurs for propulsion causes them to wear down rather quickly. They are recognizable by their contoured plastic bodies, small plastic wheels, short chutes, and lawn mower type handles with bail control bar for the augurs. Some earlier and prior generation single-stage snow blowers had 2-cycle engines, which are easier to start and maintain. These are now sought after because these engines are bullet-proof. They are no longer produced because of emissions requirements, which forced a transition to 4-cycle engines on all yard equipment.
The fourth photo at the left shows an Ariens SS522 single-stage, two-cycle snow blower.
Generally, I recommend that folks purchase dual-stage snow blowers between 24 and 28 inches, unless they have extremely long driveways, in which case they may consider wider units up to 42 inches in width. I recommend single-stage snow blowers to folks who plan to use them to clear sidewalks, small areas, and/or relatively narrow and short driveways
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