The simplest form of pump is the suction pump, and this is the form most commonly in use. Its action depends upon atmospheric pressure, which at sea level is approximately 15 lbs. to the square inch, and therefore capable of raising water to a height somewhat over 33 ft. in a perfect vacuum.
The suction pump is provided with an upper and a lower box. When the pump piston moves upward, it creates a more or less perfect vacuum behind it, and as a consequence the atmospheric pressure exerted on the surface of the water in the well, forces in water to fill this vacuum.
When the piston descends, the lower box closes and the upper box opens, allowing the water in the pump to pass through the upper box into the barrel of the pump, and be emptied out of the spout when the piston is next raised. By means of the suction pump, water can never be raised through the entire theoretical height of
33 ft., as a perfect vacuum cannot be produced in the pump, and because of the friction of the water in passing through the pipe.
The lift pump is another common form of pump, especially useful in driven wells.
The barrel of this pump, and the lower valve, are set below the surface of the water in the well, the upward stroke of the piston lifting the water without the help of atmospheric pressure as in the suction pump.
The lower cylinder is made small enough to fit into the bore of a driven well, and provided at its lower end with a strainer.
When the cylinder is not of sufficient length to reach into the water, a suction pipe may be connected to it, the pump then delivering water both by suction and lifting.
A third form is the lift-force pump. It has the same upper and lower valves that the suction pump has, but has a tight top provided with stuffing box, through which the pump rod works. At a point above the upper box, a force or delivery pipe is connected, in which is a check valve. As the water is raised above the upper box by suction, it opens the check valve in the force pipe, and passes into it. On the down stroke this check valve is closed by the water above it, thus allowing the force pipe to hold all the water that enters it. These pumps are always provided with an air chamber on the force pipe, which produces a steady stream instead of a broken one, and also prevents any strain on the pump and piping.
There is also the double-acting force pump, which delivers water on each stroke, whether upward or downward. This is a modified form of the common force pump, contains four valves, and gives a constant stream, which is very desirable for fire and other purposes.
For providing a large supply of water for small public-supply systems, for factories, institutions, and fire purposes, a system of driven wells may be used to great advantage, according to methods similar to the following, providing such supply is of sufficient amount. Below the surface of the ground, and below the frost line, a line of main pipe is laid, from the middle of which a smaller pipe of proper size is run up to the surface and connected to the power pump as a suction. At intervals along the line of main horizontal pipe, these intervals depending on the amount of the supply that exists underground, connections are taken to numerous driven pipes. These pipes connect to driven wells located several feet from the main, the entire system of driven wells covering sufficient area to enable the requisite amount of water to be obtained. Generally the driven wells are sunk at irregular depths. Such a system, operated by a power pump or pumping engine, will deliver a very large supply of water.
A few remarks on driven wells may be of value.
When water has been struck, it is necessary to know how much of the strainer is submerged, to find which information, a string with a small weight attached may be let down into the drive pipe, and when withdrawn, the length that has been wet, noted. If the strainer is entirely submerged, the water should be tested, and if found of undesirable quality the driving should continue until a satisfactory supply is obtained. An old pump is then screwed onto the drive pipe and operated until the water issuing from it comes clear and free of sand. The strainer on the drive pipe may not become clogged for a period of twelve or fifteen years, or possibly longer. When this happens, it becomes necessary to draw out the old pipe and replace the old strainer with a new one, or, if unable to withdraw the pipe, to drive a new well.