How do leaf blowers work?

In early autumn a leaf blower becomes a gardener’s best friend providing a simple and effective way of moving and collecting fallen leaves and garden debris, such as grass cuttings, when the colder weather sets in. Understanding how they work is the first step to getting the most of them this autumn.

Garden Vac 2500

Leaf Blower Air Flow Principles

Leaf blowers use centrifugal force. This can be described as an outward force in a rotating frame of reference.

The inner casing contains a motor and a fan with many blades (often referred as an impeller). The leaf blower will take the outside air and spin it using the fan blades. The act of spinning the air uses the centrifugal forces to send it through the smaller blower tube. As a result of the pressure inside the casing that has been built up by the centrifugal force, the air will shoot out of the blower tube at a very high speed.

Leaf Blower Air Speed

The overall air speed will ultimately depend on the power output from the motor and propulsion system. Often the overall air speed is measured in two different ways. Miles per Hour (MPH) is the most widely understood as it is simply the measurement of how many miles the air would travel in one hour if the velocity remained constant. Manufacturers can also use metres per second (M/S) as a similar distance-to-time measurement. In general 1 m/s equates to 2.24 mph so if a blower has a power of 55 m/s like the Flymo Scirocco 3000 this equates to a power of roughly 123 mph.

It is also important to consider cubic feet per minute (CFM) as a second power measurement. This is explained as the amount of air volume velocity that runs through the pipes. Having a high MPH but with a small volume of air won’t be able to shift many leaves at all.

As a result you would need to consider both of these numbers when researching a new leaf blower as the higher the CFM means the higher volume of air is coming out of the leaf blower. If this is then combined with a high MPH or M/S you know that the power output will be strong enough to remove the most stubborn of leaves.

Power

Cylinder displacement (CC) is another way of saying the overall power for petrol leaf blowers i.e. How fast and efficient the machine is at shifting the leaves. Overall, therefore, the bigger the cylinder displacement the more powerful the leaf blower will be. The downside to a higher cylinder displacement is that they will use up energy much faster. It is therefore important to strike the right balance between energy and power output. Electric leaf blowers are slightly different in that they report their energy output in watts.

All types of leaf blowers use this same principle of harnessing the centrifugal force regardless of what powers them. It is more common, however, that petrol machines are the most powerful as they can spin the motor faster.

Electric or battery blowers are usually less powerful but are also significantly lighter and quieter than their petrol counterparts so would be perfectly adequate with a smaller garden with not too many trees. Electricity is also much more readily available to the average household, and does not require you to store petrol or oil that would be required for petrol blowers.

Collection Vs. Mulch

Some leaf blowers have a built in vacuum setting. Most vacuums work in the same way as the blower settings as the airflow is still spun in the same way; the difference is it is directed towards the collection bag instead. There are exceptions such as the Flymo GardenVac 2700, which has a plastic strip at the bottom of the tube which directs the airflow letting you suck up the leaves and collect them in the attached collection bag. The question then is what to do with the leaves afterwards.

Several types of garden vacuums feature built-in leaf shredding capabilities where the machine can cut up/shred the leaves as it collects them. Both collection and shredding/mulching have their positives and negatives so it will be down to the individual and the garden that determines which is best. The size the leaves are shredded into can limit what they can be used for so be sure to check the shredding or mulching ratio. As an example, the Flymo Scirocco has a ratio of 10:1 so reduces the size of the leaves by 10 times the original size meaning you can collect 10 bags of leaves in 1 go.

Vaccum Fan Types

There are two main types of garden vacuum available on the market today. They are called the “Clean Fan” and the “Dirty Fan”. Both have their own benefits and drawbacks and are very much suited to different types of gardens.

The dirty fan is different because it is the fan or the impeller that shreds the leaves before passing it into the collection bag. This means there are fewer parts but and there is a higher risk of damaging the fan. This is especially true if the leaves are collected in areas with hard objects like stones. What you do get with the dirty fan however is a much higher mulching ratio. The leaves are shredded into much smaller pieces than a clean fan system would be able to achieve.

With both of these vacuum types it is very important that they are cleaned regularly to ensure they stay in working condition for longer. Debris from the fans, collection areas as well as any air inlets will all need to be cleaned to keep the vacuum working optimally.

A clean fan system on the other fan uses shredding lines to shred the leaves, and provides much more protection to the fan/impeller of the machine if you inadvertently suck up hard objects. 

Vaccum Bag Capacities

Most blower vacuums come with their own collection bags attached. Choosing the type of vacuum for the garden becomes very important at this stage due to the different fan types. This then makes the size of bag very important. Blower vacuums like the Flymo PowerVac 3000 shreds the leaves to such a small size (16:1 ratio) you can collect more leaves before you would need to empty the bag. The leaves are then pre-cut ready for your compost heap!

Clean fans that don't shred the leaves into small fragments will require more frequent emptying. Depending on how large your garden and how many leaves you will typically need to shift this may not be an issue. It would depend on the area of land you want to clear.

The other consideration you will need to make is the weight of the blower vacuum. Naturally it will get heavier as the bag fills up. The Scirocco 3000 includes a wheel so you can manoeuvre around the garden much easier as the vacuum fills up at the optimum height..

GardenVac 2700
Garden Vac 2500
Air speed 59 m/s
Mulch ratio 3:1
Weight 5.1 kg
PowerVac 3000
PowerVac 3000
Air speed 86.11 m/s
Mulch ratio 16:1
Weight 5.2 kg
Scirocco 3000
Scirocco
Air speed 55 m/s
Mulch ratio 10:1
Weight 6 kg