One of my 2nd graders was mesmerized by the foaming action of the newest
soap dispenser from Johnson&Johnson; press the pump and foam surges out the
spout and into your hand. I *thought* I could explain it quickly but even
after we tore the spout apart, it defied our attempts.
Would there be someone here that understands how the soap is processed into
foam without water being added and rubbing your hands together? Diagrams
that I might blow up and use to explain the process are _always_
In the 1950s, the a loose-fitting piston was used. On one stroke, air
and soap would be sucked in past the piston. On the other stroke, the
piston would eject the resulting foam.
Later designs used a diaphragm to create pressure. In a newer design,
squeezing a bottle pumps air and soap into a chamber above. The air
enters at the bottom of the chamber, where it bubbles up, creating foam
on top of the liquid soap.
I've seen dishwashing soap pump dispensers now that produce instant
foam. They work really well. I think Palmolive makes them. Only
problem is they cost so much more it's just not worth it. I would
guess they produce the foam by combining atmospheric air with the
liquid. It is definitely a different type of soap, you can't use
regular dishwashing liquid in them.
Did you ever think of contacting the manufacturer? If you were to
explain that your inquiry was to educate young students in the
mysteries of science, I'm sure someone at Johnson & Johnson would
bend over backwards to help you. I'll bet one of the scientists
would put something together for the kids.
My guess would be the venturi effect.
Basically the diameter of the tube that transports the soap becomes
much smaller. This creates a faster moving fluid within this smaller
section. If a tiny hole was introduced into the side of this small
diameter section it would see a vacuum. Hook air to this tiny hole
and you have a foam machine also called a venturi injector.
My brother's old rental house had a shower head like that. Looked like
just a squished piece of pipe, and first time guests would usually stick
their head out the bathroom door, and ask where the shower head was.
Worked great, though. Wish I could find a place to buy one.
I have a couple of cleaning foam sprayers used for cleaning HVAC and
refrigeration coils. The sprayers hook to a water hose and turn the
detergent in the reservoir into foam when mixed with air and water
when is sprays out of the venturi/aerator attachment. Here is a link
to a picture of one and the black tip sticking out of the sprayer
has air holes and a venturi. If you look closely, you can see it.
A fellow who owns an air conditioner repair service might let a teacher
borrow one to show the kids in the class how something like it works.
If I lived close enough, I'd let a teacher borrow one. Heck, the school
maintenance department may have one!
To understand it, look up "eductor" or "venturi" action. As air is
forced thru the tube, a vacuum is created which pulls the liquid
(soap) thru a venturi (small orifice) that mixes together with the
air. This is also the way a carbeurator works on a car.
That would produce a mist of air with soap droplets. A liquid run
through a venturi could draw in bubbles of air, but soap seems too
viscous for that.
I wonder if there is a patent number on the container. S C Johnson has
patented foaming dispensers. I wonder if there's a specific list of
ingredients. S C Johnson has patented formulas for post-foaming shaving
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