A little model pump in which five disks, 3 in. in diameter, contained in the lower front, circular case, throw 40 gal. a minute when the little electric motor is started up. The water flows out of a slit at the bottom of the upper pipe and flows back to the lower tank as seen in the foreground. This model illustrates one point astonishingly: the power can be shut off when the pump is in full operation and everything stops instantly without the slightest jar. With the power switched on suddenly, the full flow is resumed so quickly that the interval between the click of the switch and the full stream of water is too small to be determined with an ordinary watch.