How does a Vibratory Pump ("Schwingankerpumpe") work?

Question

in my aquarium Ive got a little pump for bubbling air through the water so it is substained with enough oxygen. Internaly the pump works fairly similar to old door bells, where the mains is flowing through a coil thus creating a magnetic field which moves an armature, which again presses air thorugh a hose and underneath the water's surface. (As from the German Wikipedia, https://de.wikipedia.org/wiki/Schwingankerpumpe)

Now one day I looked at my pump as I found out that its housing is very tight so that air cant come to the inside. I wrapped it up completely in plastic foil, but the air output didnt reduce. I followed the hose with my eyes, but it (obviously) didnt show any holes in it.

Still, I can use the pump (without any possible air input) to fill up a balloon.

How is that possible?

Greetings,

~Cr0n

Answer 1

aluminum foil will not stop the seepage of air through its folds. Here is how your pump works:

Most vibratory aquarium pumps have air inlets of four types:

1) underneath the bottom you may find a small tightly-squeezed-in plug of porous cloth (felt) which hides the air inlet and acts like a dust filter to keep dirt out of the air hoses.

2) cheaper air pumps use the small gap between the top and bottom halves of the plastic injection-molded pump housing as the air inlet. This does not act as a filter but it does allow air to enter the pump housing.

3) on your pump there is a place where the hose fitment (or "barb") emerges from the side or top of the pump housing through a hole. The gap between the pump housing and that hose barb can act as the air inlet for the pump inside.

4) a similar gap exists between the pump housing and where the AC mains wires enter the housing. this gap can also act as an air inlet.

I know about this because in my previous lifetime, I had to make small vacuum pumps for lab use with very little money to spend. I used aquarium pumps bought in second-hand stores and had to learn how to seal their housings airtight and install a separate vacuum inlet. this required me to know all the different air inlet locations on those things!

Answer 2

It may by creating small vacuum bobbled by just creating turbulence of enough intensity to create foam bubbles.

Agitating water can produce vacuum cavities and foam. In some cases it is taken advantage of, such as submarine torpedoes. They have been designed to create a shroud of small bubbles to reduce the skin friction drastically and move so fast as to hit the target before it can defend itself.