Water pump buying guide
Sebastian, self-taught DIY-er, Exeter183 guides
- Flow rate
- Discharge head
- Suction head
- Total Dynamic Head (TDH)
- Types of water
Submersible and surface pumps: how do they work?
All types of pump serve the same basic purpose: to move water from point A to point B. Point A might be a river, a basement or a well, and point B can be a garden, a septic tank or a house.
The water is either sucked in directly by the pump (in the case of submersible pumps) or via a suction pipe (in the case of surface pumps). The pumped water is then evacuated via a discharge pipe.All pumps incorporate a motor with a rotor which drives one or more impellers which work to draw in and then discharge the water.
The power, pressure and flow rate are proportional to one another and must be chosen based on the pumping requirements.
Depending on the type of pump and the above-mentioned characteristics, the pump may be powered by electricity (single-phase or three-phase) or petrol (2-stroke or 4-stroke engine).
Possible uses of surface pumps Possible uses of submersible pumps
Water pump types and characteristics
The pumped water can then be used to water the garden or to supply household appliances or toilets.
Boosters and pressure booster systems
If you are suffering from low water pressure in your home due to inefficient distribution, or want to regulate and/or increase the pressure of a submersible pump or a surface pump, you can install a booster or even a pressure tank in order to increase efficiency and durability, and to save money.
If you need a solution for collecting rainwater and waste water because you are too far from the mains drainage system– or because your house is below the level of the sewage network – then a lifting station is the answer.
A lifting station consists of one or more dirty water pumps and a storage tank. It can be installed underground.
These pumps have combustion engines which run on either diesel or petrol (2-stroke or 4-stroke). The exact characteristics to look for depend on how you intend to use the pump.
Functions of different types of pump
- Sump pumps are generally used to pump all types of dirty water.
- Surface pumps can pump water from wells up to 7 metres of depth and clean water from rivers (subject to local legislation) or rainwater collection systems.
- Submersible pumps are installed at the bottom of wells of over 7 metres deep.
- Boosters are used to increase the pressure of pumped water.
- Booster pumps are pumps which have a pressure booster.
- Pressure tanks are small water storage tanks, also referred to as buffer tanks.
- Lifting stations drain waste water in places where a gravity system cannot be used.
- Engine-driven pumps are surface pumps with a combustion engine.
- Pressure booster systems consist of a pressure tank, a surface pump and a booster.
Key characteristics of water pumps
Pressure is expressed in bars and measures the force with which the water is pumped. However, it is important to remember that flow rate and pressure are proportional to one another: the smaller the cross-section of the pipe, the higher the pressure, regardless of flow rate. Pressure can also be indicated as a number of metres of water column (mWC), where 10 mWC= 1 bar.
The discharge head (or static height) is the maximum height reached by the discharge pipe after the pump (it may help to picture a sloped surface).
The discharge head is given as a number of metres.
The suction head (or static lift) defines the depth of water which can be pumped by a surface or a submersible pump.
Total Dynamic Head (TDH)
The total head or Total Dynamic Head (TDH) is the sum of the discharge head and the suction head, minus friction losses (pressure losses due to the length of the pipes, bends, etc.).
It is important to carry out a thorough analysis of the water quality, because each pump/motor is designed to handle specific types of water and can become damaged if used for the wrong type. Water quality is classified as one of three distinct types based on the size of particles it contains:
- Clean water is water that contains particles smaller than 5 mm;
- Grey water contains suspended solids of up to 20 mm;
- Black water contains suspended solids of up to 25 mm.
Pump materials and operating features
Water pump design
The design and materials of a pump are determining factors when it comes to ensuring reliable and long-lasting operation. When assessing the quality of a pump, you should consider the materials used for the pump housing, the engine casing, the shaft, the impeller and all of the other fittings.
Single-stage or multi-stage pumps
Pumps can be single-stage or multi-stage. Single-stage models have one impeller which sucks up and pumps the water; multi-stage models have several impellers.
The advantage of a multi-stage pump is that the water pressure is progressively increased by each impeller. Multi-stage pumps offer greater hydraulic efficiency and are more cost-efficient and robust. Due to how they operate, these pumps are referred to as centrifugal pumps: the high-speed rotation of the impeller sucks in the liquid.
Single-phase or multi-phase power supply
Different models have different levels of power, depending on the specific characteristics. Some require a single-phase power supply, others require a three-phase power supply.
In terms of practical features, some pumps are self-priming (for easier start-up). Some models also have a water-level detection mechanism which switches off the pump when there is no water supply.
Depending on how and where you want to install your pump, you may also want to consider the number of decibels (dB) it generates (not applicable for submersible pumps).
6 tips for efficient pumping
- Some pumps have a pressure gauge to measure the operating pressure. Different types of pump have different water-tightness ratings (expressed using the Ingress Protection (IP) classification system).
- The values are usually given for a 1-inch (26 x 34 mm) pipe outlet diameter. When choosing a system with a pressure tank, remember that only 1/3 of the tank is filled with water; the remaining 2/3 is pressurised air. If you are intending to use the pressure tank to supply drinking water, check the specifications carefully to make sure the tank is suitable for this.
- It is strongly recommended to install a non-return valve (a device which prevents a pump from losing prime) and to fit a suction strainer on the end of the suction pipe (filtering device).
- Installing thermal overload protection on your electrical network will reduce the risk of short circuits in the event that your pump runs dry.
- Pumps and pressure tanks require protection against frost. If you are not going to use your pump during the winter, you need to drain it fully and ensure it has adequate protection, or move it to a place where it will not be exposed to negative temperatures or humidity. If you do not do this there is a risk of damage to the seals or premature corrosion.
- And finally, if you can't put up with the noise, or if all the calculations have put you off, there's always a bucket on a rope or indeed a manual pump!
Sebastian, self-taught DIY-er, Exeter 183 guides écrits
The DIY motto ? Learning is better than delegating… well, it's also a question about your wallet! The satisfaction? The beer at the end of the job! What do the best have in common? The influence of Gyro Gearloose, Mac Gyver and Carol Smiley depending on your generation, a good dose of curiosity, a average hand-eye coordination and a taste for risks… and if it doesn't work, try again! Advise you? I'll do my best!
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