This foam machine is built from a load of mainly scrap
plumbing parts. It is the mark IV version of the machine- the previous three
working on a different principal. All were built to make large quantities of
foam for Scout 'It's a Knockout' type games.
The unit works semi
automatically. A water feed hose is connected to ball-cock to keep it topped up.
Air is blown from a small compressor through small holes in the copper pipe,
making the foam, which exits through the hole in the front. A wooden lid covers
the top, and sits in a frame so it can be suspended. Just needs a top-up of bubble bath periodically.
There are commercial machines available, however these either have a low output (Antari machine at approx £200 from Maplins) or are very expensive if of the type used in night clubs (£3000 upwards to purchase or £400 upwards to hire). I therefore have built several, working on a couple of principles.
Foam can be defined in terms of expansion ratio (a term adopted from firefighting). A medium expansion foam is one where the air to liquid ratio is around 10:1. This produces a very 'wet' foam that is widely used for firefighting, but is difficult to make, and collapses quickly. Special detergents are also used. Equipment to produce this foam also requires high water pressures. It is for these reasons that I will not cover this in more detail.
High expansion foams are those at which the expansion ratio is between 100:1 and 1000:1. These types are much easier to produce, and will resemble the foam on your bath! There are two ways of producing this type of foam.
One is to bubble air through a detergent solution as described above, the other uses a gauze inflated by the use of an air supply (fan) which is in turn wetted by a detergent solution. The air passing through the gauze therefore produces bubbles at each hole, much like a kids bubble blower, which then conglomerate into one mass. If the mass of foam is discharged by gravity, then the device is known as a foam generator, however if the foam is projected by being picked up by a secondary airflow, or by restricting the foam outlet of the generator, a foam cannon is formed.
The first 2 machines I constructed, were very simple, made from car parts. Indeed the prototype was made from a cardboard box! (unfortunately I have no photos of this). Such machines are capable of producing approximately 1/2 cubic metre (500 litres) of foam a minute. The machines consist of a wooden box, approximately 18" to 2ft long.
At one end of the box is mounted a car radiator fan, set to blow through the box. On both ends of the box are holes, the same diameter as the fan. Both holes are covered with a 1/4" square galvanised mesh. The inside end of the box opposite to the fan, over the hole is covered in a fabric mesh/ gauze. The gauze should have holes no larger than about 1/8", but should be made of thick thread that will hold a reasonable amount of fluid (ie not net curtain material).
A windscreen washer pump is mounted inside the unit, with the input taken out on a tube a couple of metres long, with a foot filter mounted.The pump feeds a number of garden micro irrigation nozzles, mounted approximately 8 inches inside the gauze. A degree of trial and error is required to determine the number of nozzles required, their distance from the gauze, and arrangement, so that maximum, and even wetout is acheived. Power is arranged so that it is switched seperately to both the fan and pump, to give a degree of control. The box is painted, sealed and provided with handles.