Small relatively quiet vacuum pumps like that are membrane pumps. An aquari=
um
pump is an extreme example but most small ones are crank driven motor, not
electromagnet. For one offs I'd go after spare parts for equipment. A lot o=
f
things use them, not always as vacuum (sometimes as pressure source and
sometimes for transfer - membrane pumps do not contaminate the medium at al=
l -
example: CO2 and CO tester/meter). The price will not be nice in ones. Also
automatic blood pressure meters use them (cuff inflation).

Your vacuum-in-the-pool adventures are noted. Maybe you should know that an
unregulated vacuum motor will pick up speed when the inlet is closed, as it
pumps down the inlet, and density decreases. That increases efficiency and =
also
suction (!). That may explain what you saw (sudden suction). Centrifugal pu=
mps
with impeller above the water line are very temperamental sometimes and the=
re
are known cases where they oscillate in the inlet column until something gi=
ves.
That being said, there are several water rated shop vacuums which route the
exhaust through the motor (!) water and all. I was pretty shocked when I
realized this. That's the trashcan sized kind of device that will happily v=
acuum
nails and screws and chips from the lathe. They have a deflector apron whic=
h
prevents direct water spray onto the brushes and that's it. Scary. And I me=
an
big brand names (like H***). I once used one to remove almost 5cm of water =
from
a small flooding in a sizable lab before I found out where the water goes
inside. Amazing. And yes it is explicitly rated for liquid water suction. I=
t
made about 400mmHg of vacuum at full speed when stalled.

As to breathing vacuum exhaust, don't ever. Not even with a dust filter. An=
d
compressor air is as bad or worse (suspended oil particles). You can get re=
ally
hurt like that.

-- Peter


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