Cyclone build part 2 – Air Inlet and Ramp

Before we go on to the main upper body of the cyclone, lets get the air ramp and air inlet ready for it. The air inlet is a rectangular section passage which fires the dust laden air into the main cyclone. The angle at which it does this is crucial (something many commercial cyclones ignore). It wants to be sloping downwards, at the outside edge of the upper body. The inlet needs to be a certain length of straight smooth passage, so that the air entering the cyclone is in a nice turbulent-free stream.

As Pentz explains, horizontal inlets are one of the main culprits, when it comes to unwanted turbulence inside a cyclone:

The turbulence inside a normal cyclone is so high it keeps these particles airborne and separates almost 0% of the airborne dust particles sized much under about 25 to 30-microns.

Having the inlet tall but narrow helps keep the dust and particles near the outside of the cyclone. That way when they enter the upper body, they don’t fly across and hit the side because they are already right by it. This reduces general bouncing about madness, and helps establish a smooth spiral path for the dust from the outset.

The air ramp continues the downwards angle of the inlet. It ensures that the air does not whiz round and hit into the backside of the inlet, or the new air continuing to stream in,(both of which would be a cause of turbulent badness).

Making the cyclone’s ‘Air Ramp’

For the air ramp use 1.5mm thick polycarbonate. The air ramp size must be bigger than the diameter of the upper body, because it is stretched out in a spiral when it fits inside. The diameter is calculated with a crazy maths type equation from this website: http://www.math.cornell.edu/~dwh/papers/EB-DG/EB-DG-web.htm

The air ramp can be cut out on the bandsaw using a simple circle cutting jig (you will need a circle cutting jig of some sort – even if it is as simple as this ‘screw in board’ affair). As the outer ring is not continuous, you can get in and cut the inside circle with the bandsaw blade.

Here is the cyclone’s ‘air ramp’ cutting diagram and measurements (click for a closer look).

Making the cyclone’s ‘Air Inlet’

For the inlet I used 3mm thick polycarb. To make the air inlet it is useful to cut with a bevel edge of 45 degrees. That way when it is in use the suction force on the inside of the inlet, rather than weaken the join (as it would in the case of a standard butt joint), actually strengthens it.

One way to get the correct entry angle, is to cut the whole thing after gluing it together. This might seem easier than working out all the individual lengths (but I have now done this for you – see diagram further down), but is a bit risky because the violent action of the bandsaw can damage joints. After getting the angle right, it is ready to be put into the upper body (see next step).