A cistern pump works by using mechanical force to create pressure, moving collected water from a storage tank (cistern) into a household's plumbing or irrigation system, especially when gravity alone is insufficient for water delivery.
What is a Cistern Pump?
Cisterns are tanks designed to collect and store water from an outside source, such as rainwater from a roof. This collected water is then piped into a household water system for various uses, from flushing toilets to irrigating gardens. While it's possible for water to transfer from a cistern to a household system solely through gravity if the cistern is positioned significantly higher than the main water inlet, this setup is not typically the case for most homes. Therefore, a cistern pump becomes an essential component to ensure a consistent and adequate supply of pressurized water throughout a property.
A cistern pump essentially takes the non-pressurized water from the cistern and boosts it to a usable pressure, enabling it to flow through pipes to faucets, showers, and appliances.
The Mechanics of a Cistern Pump
The core function of a cistern pump involves converting electrical energy into hydraulic energy, pushing water where it needs to go.
Key Components
A typical cistern pump consists of several vital parts:
- Motor: Provides the power to drive the pumping mechanism.
- Impeller (for centrifugal pumps) or Ejector/Venturi (for jet pumps): The primary component responsible for moving water.
- Pump Housing: Contains and protects the internal components.
- Inlet: Where water enters the pump from the cistern.
- Outlet: Where pressurized water exits the pump towards the household system.
- Pressure Switch (often external): Senses water pressure and turns the pump on or off to maintain a desired range.
- Pressure Tank (often external): Stores a reserve of pressurized water, reducing pump cycling and providing a more consistent flow.
The Pumping Process
The process of moving water from the cistern to the household generally follows these steps:
- Initiation: When a faucet is opened or water pressure drops below a set point (detected by a pressure switch), the pump's motor activates.
- Water Entry: Water from the cistern enters the pump through its inlet.
- Pressure Generation:
- Centrifugal Pumps: An impeller, a spinning disc with vanes, rapidly rotates. As water enters the center of the impeller, centrifugal force throws it outward, increasing its velocity. This velocity is then converted into pressure as the water moves towards the pump outlet.
- Jet Pumps: A motor drives an impeller to create a high-velocity jet of water that passes through a venturi (a constricted passage). This creates a low-pressure area, or vacuum, which draws more water up from the cistern to mix with the jet, boosting it into the discharge pipe.
- Delivery: The now-pressurized water is pushed through the pump's outlet, into the household's plumbing system, and on to its point of use.
- Shutdown: Once the demand for water stops and the system pressure reaches a predetermined high point, the pressure switch signals the pump to turn off, conserving energy.
Pressure Regulation
To ensure a smooth and consistent water supply, cistern pumps are often integrated with a pressure tank and a pressure switch. The pressure tank acts as a buffer, holding a volume of pressurized water. This prevents the pump from starting every time a small amount of water is used, thus extending the pump's lifespan and maintaining more stable pressure. The pressure switch monitors the system pressure, turning the pump on when pressure drops to a low set point and off when it reaches a high set point.
Types of Cistern Pumps
Cistern pumps are primarily categorized by their placement and how they move water. The two most common types are submersible pumps and shallow well/jet pumps.
Submersible Pumps
- How they work: These pumps are designed to be placed directly inside the cistern, fully submerged in the water. They push water upwards from below.
- Advantages: They are very quiet as the water dampens the motor noise. They are also self-priming (no need to fill the pump with water before operation) and generally very efficient because they push water rather than pull it.
- Disadvantages: Servicing can be more challenging as the pump must be retrieved from the cistern.
Shallow Well/Jet Pumps
- How they work: These pumps are installed outside the cistern, typically above ground. They draw water up from the cistern through a suction pipe, creating a vacuum using a jet mechanism.
- Advantages: Easier to access for maintenance and repairs since they are not submerged. They are often paired with pressure tanks for optimal performance.
- Disadvantages: Can be noisier than submersible pumps. They have limitations on how far they can lift water via suction (typically up to 25 feet). They may also need to be primed (filled with water) before their initial use or if they lose prime.
Here's a comparison of these two common pump types:
| Feature | Submersible Pump | Shallow Well/Jet Pump |
|---|---|---|
| Placement | Inside cistern, fully submerged | Outside cistern, above ground |
| Noise Level | Very quiet | Can be noisy |
| Priming | Self-priming | May require manual priming |
| Maintenance | Requires removal from cistern (more difficult) | Easily accessible (simpler) |
| Efficiency | Generally higher (pushes water) | Can be less efficient (pulls water) |
| Suction Depth | Not applicable (pushes from below) | Limited (typically up to 25 feet) |
| Best For | Deep cisterns, quiet operation, reliable flow | Accessible cisterns, easier servicing, shallower suction needs |
Why Use a Cistern Pump?
Cistern pumps are indispensable for various applications, primarily to:
- Provide Consistent Water Pressure: For domestic uses like showers, toilets, dishwashers, and washing machines, a pump ensures water flows at an adequate and steady pressure. For example, a home using collected rainwater from an underground cistern relies on a pump to deliver water to bathrooms on upper floors.
- Supply Water for Irrigation: Pumps allow for efficient distribution of cistern water to garden hoses, sprinklers, or drip irrigation systems.
- Overcome Elevation Changes: When the cistern is at a lower elevation than the point of use, or when water needs to be moved over a significant distance, a pump provides the necessary force to defy gravity and friction losses.
- Enhance Water System Reliability: Paired with pressure tanks, pumps create a stable and reliable water supply, reducing fluctuations.
Factors to Consider When Choosing a Cistern Pump
Selecting the right pump ensures efficient operation and longevity of your water system. Key considerations include:
- Cistern Size and Water Demand: The pump's flow rate (gallons per minute, GPM) should match your household's peak water usage. A larger household with multiple fixtures running simultaneously will require a higher GPM pump.
- Head Pressure and Flow Rate: "Head" refers to the vertical distance the pump must push water (total dynamic head includes elevation, pipe friction, and desired outlet pressure). The pump must be powerful enough to overcome this total head pressure while delivering the required flow rate.
- Power Source: Most pumps are electric (120V or 240V), but solar-powered or even manual pumps are available for off-grid or specific applications.
- Water Quality: For potable (drinking) water systems, the pump materials must be rated safe for drinking water and resistant to corrosion. Consider filtration needs before the pump to protect it from sediment.
- Noise Level: Submersible pumps are generally quieter if noise is a concern, especially in residential areas.
Maintenance Tips for Cistern Pumps
Regular maintenance helps ensure your cistern pump operates efficiently and lasts longer:
- Inspect Regularly: Check for any signs of leaks, unusual noises, or vibrations that could indicate a problem.
- Clean Inlet Screen: Periodically clean the pump's intake screen to prevent blockages from sediment or debris, which can reduce efficiency and damage the pump.
- Check Electrical Connections: Ensure all wiring is secure and free from corrosion.
- Winterize (if applicable): In colder climates, if your pump is exposed or not submersible, follow manufacturer guidelines for winterization to prevent freezing and damage.
- Monitor Pressure Tank: If using a pressure tank, check its air charge periodically to ensure it's functioning correctly and preventing the pump from cycling too frequently.
