How to Choose a Submersible (Drainage) Pump
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1. What is a drainage pump, principle of operation
A drainage pump is a special equipment for draining a tank, pit, or room, the main feature of which is the ability to pump dirty water. Its main task is to remove water to prevent flooding and related problems. There are surface pumps, which, as the name suggests, are installed directly on the ground next to a well or water reservoir. They are easy to use and maintain but are not very productive.
are installed on the ground next to the place from which it is necessary to pump water.
In this article, we will talk about submersible pumps, which are immersed in water, are more powerful and productive models, and are capable of pumping large volumes of water in a short period of time. Their main components are:
- Housing — protects internal mechanisms from moisture, dirt, and mechanical damage.
- Electric motor — starts the pump.
- Impeller — rotating blades providing water suction.
- Grate (filter) — prevents too large particles, debris, leaves, branches from entering the pump.
- Discharge pipe — water exits through it and is diverted through a hose to the desired location: sewer, drainage, tank, etc.
The drainage pump is immersed in water and installed almost at the very bottom of the flooded area. When the engine is turned on, the blades start to rotate and create a suction force that draws the dirty liquid inside. After this, the water is pushed out under pressure, simultaneously helping to cool the electric motor.
Pumps are divided into several types based on the principle of operation:
- Centrifugal. An impeller inside rotates at high speed. Under centrifugal force, water is thrown from the center to the edges and exits into the pressure pipe. The main advantages of such pumps are high efficiency, stable operation, and the ability to pump large volumes of liquid.
- Vortex. The mechanism provides fluid swirling, thereby preventing siltation and sedimentation of impurities at the bottom. Often such models are more compact than centrifugal ones, create high pressure, and are resistant to air blocks. At the same time, they have lower performance and handle mechanical impurities poorly — wear out faster.
- Vibration. Pumps do not contain rotating parts and use vibrations instead to transfer water. A special electromagnetic core creates pulsations, pushing water through valves. Such devices are inexpensive, easy to use, and compact — they can work in narrow shafts. However, they are short-lived, not recommended for pumping heavily polluted water with a large number of solid particles, and vibrations can damage the walls of the well.
- Screw. A rotating spiral screw (screw) inside smoothly moves water to the exit. This mechanism provides a stable flow and is resistant to various contaminants, viscous liquids, and even sludge masses. Among the drawbacks are relatively low performance, complex maintenance, and high cost.
2. Types of drainage pumps by purpose
A distinctive feature of drainage pumps is that they can work with both clean and dirty water, although they are more often used in the latter case. But contaminated water can also vary, so when choosing a device, it’s important to at least roughly understand which impurities and debris will be dealt with, as this directly affects the type of pump.
2.1 For clean water
This refers not to crystal clear, but relatively clean water, usually with impurities up to 5 mm in size. For example, if a pump is needed to extract water from pools and wells.
2.2 For dirty water
Such pumps handle impurities between 5 mm and 30 mm. They are used to eliminate flooding consequences of basements and ground floors of buildings, also applied at construction sites and for cleaning pits.
2.3 For sewage
An "enhanced" version of pumps for dirty water capable of handling larger contaminants — 50 mm in size or even more. Obviously, this primarily works for sewage, but it can also be used with flood and wastewater with lots of debris, often large.
2.4 For chemical liquids
A special class of equipment designed to work with aggressive, toxic, and corrosive substances: various acids, alkalis, solvents, oil products, resins, and dangerous wastewater. They are used in industrial enterprises, laboratories, chemical warehouses, car washes, agricultural facilities (for instance, for fertilizers or herbicides application), and treatment facilities. These pumps are rare because they must have special design features to safely transfer chemicals without breaking down or contaminating the pumped medium. This includes strong housing materials, a sealed design, resistance to corrosion, and different temperatures and pressures.
The diameter of impurities in the pumped water affects the pump’s design, or more precisely — the size of the intake openings and the internal pump part. Since even in clean liquid, large contaminants can occur, some pumps are equipped with choppers: they grind them into smaller particles, which the equipment can easily handle. Having a chopper increases the device's reliability and durability, especially relevant when working with heavily polluted liquids and sewage.
3. Main characteristics
Having figured out the intended purpose of the pump, let's proceed to its key characteristics.
3.1 Power
This parameter affects performance, speed, and volumes of pumped liquid, resistance to blockages, overloads, and overheating. Low-power models (up to 500 – 700 W) can only handle light tasks — for example, pumping clean water from a pool or reservoir, draining rainwater systems, and small basements. Devices with more than 1000 W handle dirtier water and higher lifts — for instance, in areas after rain. Power up to 2000 W allows for heavy loads in home use and even on construction sites. For heavily polluted water, heavy fractions, and aggressive environments, power exceeding 2000 – 3000 W is needed.
Certainly, it’s better to choose a pump with a power reserve, but not too much, as it affects the price, dimensions, and energy consumption. Also, keep in mind that high power is not always equal to high performance, so it is better to also consider other characteristics described below.
3.2 Performance
This indicator signifies how much water a pump can move in a certain time. Measured in liters per minute (L/min) or cubic meters per hour (m³/h). It's important to understand that performance influences work speed. For instance, with a 12,000-liter pool, a pump with a performance of 12,000 L/h would manage in 1 hour, whereas a less productive model (6,000 L/h) would take twice as long.
For household purposes, like draining a basement or pool, a pump with a flow rate of 100 to 200 liters per minute (6 – 12 cubic meters per hour) is usually sufficient. For pumping larger volumes of water, choose more productive devices.
3.3 Head
The head is, simply put, the height the pump must lift water to: for instance, outside, into a sewer, or another tank. The higher this height — the more power and performance required from the pump. To determine the optimal head, simple mathematical calculations need to be performed. It's crucial to consider how many meters of pipe are necessary for the work, including both vertical sections (water lift) and horizontal (the length the water travels). The calculation uses this ratio:
- vertical distance — 1:1
- horizontal distance — 10:1 (10 meters horizontally equals 1 meter vertically)
Having determined the sum of all pipe lengths and distances, at least 25 – 30% should be added to account for losses (friction in pipes, bends, valves, etc.).
As an example, let's calculate the head for a pump that needs to evacuate water from a basement 3 meters deep, lead it through pipes 20 meters long, and lift it into a 1-meter tank. It turns out to be:
3 m + 2 m (20 m horizontally = 2 m vertically) + 1 m + 30% = required head 8 m
Most often, models with heads up to 20 meters are chosen for domestic needs. For complex tasks, more durable and powerful devices are provided, capable of lifting water to heights of 50 – 100 meters or more.
3.4 Submersion depth
The name "submersible pump" indicates that the equipment is installed underwater, unlike surface models. Meanwhile, the manufacturer specifies a maximum permissible depth to which the pump can be submerged without risking damage to its design, electric motor, or insulation. Often for standard drainage pumps, this measure reaches 5 – 7 meters, and for fecal ones — up to 10 meters.
Note that if the bottom is flat and not dirty, the pump can be installed directly on it or slightly raised with a stand or cable. Yet if the bottom is uneven, soft, unstable, silted up, and too dirty — it’s recommended to raise the pump by half a meter or even more to improve performance and avoid blockage. For this, the device is suspended using a safety cable.
3.5 Water temperature
Most drainage pumps are designed for pumping cold or warm water (up to 35°C). Fecal pumps are rated for temperatures around 40°C and in short-term use can tolerate more. However, there are specialized models with thermal protection that can withstand temperatures up to 100°C. These are primarily the above-described devices for chemical liquids. Keep in mind that exceeding the allowable temperature leads to overheating, engine failure, quick spoilage of bearings, impellers, and other internal parts.
4. What else to pay attention to
4.1 Housing material
The best option is stainless steel: it’s corrosion-resistant, strong, durable, does not deform, and does not crack over many years of active use. Cast iron also possesses similar strength but costs more. If the pump is required to work with aggressive, acidic, alkaline liquids — it’s preferable to choose specialized models with a polypropylene or special fiberglass housing, often with reinforced reinforcement.
4.2 Impeller / screw material
Since this is the main part of the working mechanism, it should also be made from quality materials.
- Plastic — cheap and light material, corrosion-resistant, but wears out quickly and doesn’t handle contact with solid impurities in water well. More resistant and robust are various technopolymers and composites.
- Stainless steel — a strong, heat-resistant material, resistant to sand, but not cheap. Used in high-performance pumps.
- Cast iron — combines a relatively low price (compared to stainless steel) with good strength, although it is more sensitive to corrosion.
- Brass — quite an expensive alloy (usually of copper and zinc) that ensures strength, durability, and corrosion resistance.
- Aluminum — has all the advantages of steel and cast iron (strength, durability, corrosion resistance), but is noticeably more expensive, therefore found in premium-class models infrequently.
- Bronze — not afraid of corrosion but has a significant disadvantage of being very costly.
4.3 Safety systems
Typically, for safe operation and extended service life, drainage pumps have protective functions. An automatic thermal relay protects the engine from overheating by simply turning it off. Dry run protection prevents operation without water, as it can lead to severe loads and even breakdowns. Often this is achieved with the help of a float switch, which monitors the liquid level and, if it is below the allowable norm, turns the device off.
4.4 Power source
In most cases, drainage pumps operate from a regular household socket at 230 V, but more powerful models used in industry and construction require connection to a three-phase network at 400 V.
Under conditions of no electricity, autonomous units with their engines — gasoline or diesel are handy. They are powerful, productive, noisy, require refueling and maintenance but are categorically prohibited for indoor use due to carbon monoxide.
There are also a few battery-powered devices that work independently without needing a socket or electricity. But these are quite weak, low-power pumps intended only for clean water and small volumes, and their battery runs out quickly.
and are designed for pumping small volumes of clean water.
4.5 Diameter of the discharge outlet
This concerns the opening through which water exits the pump, and the larger the opening — the faster and more productive the pump. Typically this value is 1” (25 mm), 1 1/4” (32 mm), 1 1/2” (38 mm), and 2” (50 mm). Through this opening, a hose or pipe connects, directing the pumped liquid to the desired location, so they must match in size. For example, if a very narrow hose is connected to a powerful pump, excess resistance is created, reducing performance and pressure, and the motor may overheat.
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