After a well is once regulated or balanced there is but little occasion to move the adjusting wheel or valve, the starting and stopping of the flow of any particular well being accomplished by means of an ordinary valve or plug cock on the air pipe at or adjacent to the well.
One Central Station of suitable capacity will operate several wells no matter how far apart. The necessity of maintaining a number of separate pumping plants is thus done away with, and in taking a supply of water from an underground source the wells can be located without reference to the power plant, and at such distances apart as will best maintain the highest average pumping level.
Although the principle of the action governing all pumps of this description is so simple, there are a number of factors having a direct influence upon the performance of the pump, which have been expressed in the following terms by a well-known expert:
(a) Depth of submersion of point of air discharge below still water surface.
(b) Velocity of water at point of air discharge.
(a) and (b) determine the necessary air pressure. If (a) is constant, the pressure decreases when (b) increases.
(c) Area of main, or water discharge pipe.
(d) Net lift to point of water discharge, including velocity head at that point.
(e) Volume of air (at atmospheric pressure) discharged per unit of time.