In message ,
newshound writes
On 23/06/2019 09:42, Graeme wrote:
It does indeed pump air, and I assume, although haven't looked, it
is just a basic 12v DC motor driving an impeller.

They are usually diaphragm pumps. The Brrrrrr sound is the give-away.
May be a motor and crank, may be like a door-bell, i.e. a solenoid with
a breaker switch on the arm. Screen washers are often impeller, note
the higher frequency sound.

Excellent, thank you.
--
Graeme