There are several basic considerations in choosing pump equipment, including:
Quantity of water yield from source
Quantity and rate of demand of users
Depth from ground level to pumping water level
Size of well
Power source and its reliability
Initial cost and cost of operation
Ease of maintenance
Availability of replacement parts
Mineral content of water
(presence of sand and dissolved materials)
It is recommended:
Pumps be installed in accordance with the manufacturer’s recommendations, and, if applicable, local building codes and/or ordinances.
Pumping equipment be installed to prevent the entrance of contamination of objectionable material, either into the well or into the water that is being pumped.
The pump be located to facilitate necessary maintenance and repair, including overhead clearance for removal of drop pipe and other accessories.
The pump be suitably mounted to avoid objectionable vibration and noise, and to prevent damage to pumping equipment.
The pump controls and/or accessories be protected from weather.
There are no general rules for the best type of pump for a given installation. Each type of pump has its own advantages and limitations. As new pumps are developed and old ones improved, the range of best usefulness changes. Even among the various pump manufacturers , range of best usefulness of the different types of pumps varies.
The suction requirements (or the pressures necessary to move the water from the well to the ground level) are factors that must be considered in pumping equipment selection.
Shallow well type pumps draw water from the ground by creating a vacuum at their inlet. This vacuum, or reduced pressure area, allows the atmospheric pressure to push the water into the suction pipe and up to the pump. The practical limit for shallow well type pumps is a lift of 25 feet, at or about sea level. Several kinds of pumps are used for shallow well applications in water systems. These include jet, piston, centrifugal, regenerative turbine and helical rotor pumps.
The performance charts for these pumps usually separate the suction lift, or depth to water, from the discharge pressure. The total suction lift consists of the vertical distance from the inlet to the pumping water level plus the friction losses in the suction piping.
Deep well type pumps have their suction inlets submerged. Several kinds of pumps are used for deep well applications in water systems. They include deep well reciprocating, jet submersible, and vertical turbine. The capacity charts for jet pumps usually separate the depth to water from the discharge pressure.
When the vertical distance from the pump to the pumping water level is known and the suction and pressure pipe sizes recommended by the pump manufacturer are used directly, without considering friction losses in the suction and pressure piping. When there is a long offset or distance between the top of the well and the pump, the pipe sizes must be increased (as recommended by the pump manufacturer) to maintain pump capacity.
Submersible deep well pumps are usually rated on the basis of the pressure at their discharge casting. The charts generally take the vertical lift in feet out of the total pump discharge pressure. If the vertical distance to the pumping water level is known, the pump capacities can be found at the various pressures at ground level. Normally, these charts do not account for the friction losses through the piping and fittings in the well and into the house. These losses should be subtracted from the discharge pressure values shown in the manufacturer’s charts.
It is recommended that the operating capacity of the pump shall not exceed the capacity, or yield of the source, whether adequate or limited. This is of the utmost importance, since overpumping a well can be a cause of serious damage to the well or pumping equipment.
There are several ways to prevent overpumping.
Select a pump that will produce no more than the source will yield at the desired operating conditions.
Use 30 feet of tailpipe below the jet on deep well jet installations.
Use a vertical suction pipe of 30-foot length on shallow well jet installations.
Use a higher setting of the pressure switch to reduce output to match yield of source, within the limits of the pumping equipment.
Use low pressure cut-off switches and low water level cut-off switches.
Use flow control devices.
A second pump, of the shallow well type, delivers water from the atmospheric tank to a hydropneumatic tank. This pump, operating between two tanks, delivers the capacity and pressure.
The same basic type of pumping equipment is recommended for limited sources with the exception that extreme care must be taken to assure that the source of supply is not overpumped.
In the two-pump system, the well pump usually operates for extended periods of time. Therefore, it must be rated for continuous duty. Pumps certified under Water Systems Council Standards are rated for continuous duty.
An elevated atmospheric tank may be used in place of the second pump in the two-pump system. The height of the tank is determined by the pressure needed.
The pumping equipment recommended for surface sources would be the same as that recommended for adequate sources. It would generally be of the shallow well type. Surface water sources generally require purification and treatment. Refer to Section III.