All those who live or work in places where drinking water supply networks do not arrive know the dependence of a private well to extract clean and safe water from underground sources.
This extraction is carried out by means of an electromechanical system, whose main component is a water pump designed to handle water suitable for human consumption. The pump collects water from a well and delivers it to a storage tank where it is pressurized and preserved until it is used.
In this article we are going to address precisely that situation, mentioning some of the considerations that we must take into account when choosing a suitable pump for our well.
Types of well pumps
First of all, we should know that the majority of well pumps are centrifugal pumps that fall into two main categories:
a) Jet or injection pump: it is a device that can be located on the surface or in the subsoil and draws water from the well by means of a suction mechanism, made by an ejector unit composed of a nozzle and a venturi tube, through one or two pipes directed to the well. It is often combined with a storage tank or tank and depending on the location of the ejector unit, they are subdivided into:
- Jet pumps for shallow wells: with the ejector located in the pump body and a single tube directed to the well.
- Jet pumps for deep wells: with the ejector located below the water level and two pipes directed to the well.
b) Submersible pump: its fundamental difference with the jet pumps is the operation. A submersible pump does not suck water, but pushes it up and, since this action requires less energy, it is usually more efficient to use in deep wells. It has a single tube from the well that can be connected or not to a storage tank. This type of pump is installed near the bottom of the well and pumps water only when needed. Precisely because it is permanently submerged in water, this pump is self-priming and not susceptible to the problem of cavitation, common in jet pumps.
As we can see from this description, the choice between a jet pump and a submersible pump will depend mainly on the depth of the well and the diameter of the pipe inside the well jacketing. Let\’s see how to choose the pump according to these parameters.
How deep is the water?
The first consideration we must make is the distance that water must travel to reach the surface. If the area where our house is located has a stable water supply close to the surface, that is, a high water table, access to water will be much easier. Deep wells, on the other hand, will require additional considerations. In general terms, we can decide the type of water pump according to the following well depth criteria with respect to the location of the pump:
- Depth less than 8 meters: choose a jet pump for shallow wells.
- Depth between 8 m and 35 m: choose a jet pump for deep wells.
- Depth between 35 m and 120 m: choose a 4-inch submersible pump.
To find out the depth of our well, just consult the report delivered by the construction company. If we do not have that report, there are several methods to perform this measurement, even with special probes that can be purchased commercially. However, one of the simplest methods requires access to the wellhead. We open the lid that covers the mouth and lowers a fishing line with a float and a weight on one end. When we no longer feel the weight on the line, it is because it is floating. We measure the magnitude of the line dropped in the well and thus we will know how deep it is to the water. If the pump will not be located at the level of the wellhead, we must make sure to add, at the measured distance, the height from the wellhead to the pump.
What size pump is necessary?
This is determined based on our domestic water requirements. In a previous article, we detail a table with the typical consumption of water in a home. There we also mention that the discharge capacity of a pump is the speed at which water flows from the source to the discharge point and is measured in liters per minute (LPM) or gallons per minute (GPM). A typical house with 3 to 4 rooms requires between 30 and 50 LPM. When determining our water needs, it is convenient to add between 3 and 4 LPM for each appliance that uses water, that is, washing machine, dishwasher, refrigerator, tap, shower and garden sprinkler, for example.
However, we must not exaggerate. Even if our calculations indicate that we require a pump with a high discharge capacity to meet our domestic needs, it is very likely that a very high capacity pump will generate energy inefficiency and lower performance.
On the other hand, if we are going to replace an existing pump, we have to choose a unit with the same discharge capacity. However, we may require more capacity if we have added more artifacts or if the house has more inhabitants.
Key components to consider
Pumps include bearings, impellers (or rotary vanes), electric motors, motor bearings, valves and control switches. Of these, there are a number of components, both pump and additional, in which we have to pay special attention in terms of their presence and quality. Let\’s see the main ones.
Foot valve and check valve: pumps are primed faster if the suction line incorporates a foot valve and a check valve. These allow the regulation of the flow and, therefore, of the motor consumption, thus avoiding overload. Both valves allow flow in only one direction to the pump and keep the water inside the suction line, retaining the priming for the next pump cycle. The foot valve comes with a filter and flange at one end, while the check valves come with a flange at both ends, allowing its location within the line.
Diffuser cones: it is recommended that the length of the eccentric diffuser cone located in the suction be seven times the difference in section, or diameter, between the inner holes of the suction pipe and the inlet port of the pump. As for the length of the concentric diffuser cone located in the drive, it is convenient that it is seven times the difference in section, or diameter, between the inner orifices of the discharge or discharge pipe and the outlet hole of the pump body.
Pressure switch: this component automatically opens and closes the water passage, depending on the pressure setting. When the pressure reaches a value between 2.5 and 4 bar, the pressure switch turns off the pump. When the pressure gradually decreases due to the use of water, the pressure switch turns the pump on again, repeating the cycle. If the pump does not turn off, it could indicate a problem with the pressure switch setting. A pump will also not shut down if the well water is too low or if there is a loss in the pipe.
Starter relay: float switches, 24-hour timers, and controllers are commonly used devices that send a signal to start the pump, which is received by the starter relay. This relay must be specific for the coil voltage, according to the signal device, allowing the closure of a contactor and the flow of electricity between the power source and the pump motor.
Tank or storage tank: it is a component that helps regulate the flow of water and maintain constant water pressure for the proper functioning of the connected devices. When the water is pumped to a storage tank, the water is compressed, so that it can travel evenly throughout the entire plumbing system of the house. A pump that turns on too often could indicate the need for recharging or even the possibility of loss.
Pressure-sensitive pumps and controllers within the line: this type of system provides greater water pressure without the need for a pressure tank.
Safety rope: it is important to acquire them if we decide on a submersible pump, as they will help recover the pump from the well for maintenance or repair purposes.
Life of a well pump
A jet pump or one or two tubes can work up to 20 years before requiring a replacement. A submersible pump placed in low sediment-water can reach 15 years, although the presence of more sediment can shorten that period.
There are also other factors that we must emphasize to acquire and maintain a pump that will give us a long service life.
Duty cycle: a pump with an intermittent duty cycle will have a longer life than a pump with very frequent or continuous use.
Motor size: an electric motor of greater power (ie 1 or more horsepower) will last longer than an electric motor of fractional power. The more powerful the engine, the less time it will take to run.
Engine quality: the type and quality of electric motor bearings, together with lubrication requirements, affect the life of a pump.
Toilet sediment: the sediment is abrasive and can wear out the pump bearings. While submersible pumps can be used in shallow wells, the presence of algae, silt, sand and other pollutants typical of shallow water can shorten their useful life.
A quality installation: the installation of a pump is not just to connect it. It is also important to ensure the proper location of check valves, filters, and wiring. Ensuring a good installation, whether by a company or a professional, is a detail that should not be overlooked.
Safe well performance: for this, it is essential that the pump capacity is equated with the output speed. Otherwise, it can dramatically reduce the life of the pump.
Cavitation: this phenomenon occurs when air is introduced into the chambers or the impellers of the pump, which can cause overheating of the moving parts and their consequent mechanical damage. This situation will require more pump work to meet the same demand, reducing engine life. Cavitation can be caused by a series of problems, such as:
- Improper well performance: pumping water above the safe well performance can introduce air into the pump.
- Large pumps: the lack of coincidence between the flow of the well and the output speed of the pump can cause a strong vacuum that, in turn, will cause the bubbles to dissolve in the water in the form of bubbles.
Shutters: installing a shutter provides control water cut to protect the pump from damage by excess water, and the shutter allows the flow of water in the well, but stops or slows the additional water supply.
If once installed, we suspect that our pump is not working properly, it will be convenient to consider the following warning signs:
- Low water pressure: a significant drop in water pressure in the shower or other appliances could indicate a problem with the pump.
- Intermittent cycle: if the pump is turned off and on for no apparent reason, there could be a problem with the pressure control switch.
- Short cycle: If the pump shuts down too quickly, there may be a loss of air pressure in the storage tank due to an obstruction or a faulty control switch.
Other well pumps to consider
It is possible that, in addition to not having a potable water supply network, we also do not have electricity at the site of the pump, for example, as is the typical case of country cabins or other properties in isolated places. In that case, are there pumps for alternative wells? In fact, yes and for this, we present some examples that we can consider:
Solar pumps: as we pointed out on another occasion, these pumps do not need an external power supply and work more efficiently and profitably than traditional pumps. Solar panels provide the energy needed to pump water from several meters underground. Recent technological advances have significantly reduced costs, so solar energy systems are now more affordable.
Manual pumps: they are very light and economical to ensure constant water supply. A manual pump is ideal for light and temporary use and can be easily removed from a well.
Hydraulic ram pumps: use the force of water from rivers or streams, combined with hydraulics, to raise water to almost 50 m from a given location. They are mainly used in the agricultural sector since it is very possible that water from waterways is not suitable for drinking.
Pneumatic pumps: the air pumps are driven by air instead of electricity and are typically used in commercial and industrial environments.