Surface pump buying guide
Sebastian, self-taught DIY-er, Exeter187 guides
- Flow rate
- Total head
- Supply height
- Discharge height
- Pressure drop
Surface pump: a definition
For this pumping to take place, the surface pump creates suction via one or more turbines or impellers rotating at high speed.
A surface pump, as the name suggests, remains on the surface of the water (unlike a submersible pump). Surface pumps can also be used as part of a hydrophore group - alongside a booster. Surface pumps are designed for water sources less than 8m deep, beyond which the submersible pump takes over.
The key characteristics of a surface pump are flow rate, pressure, discharge height and materials - principally of the pump body.
How do you determine the discharge head, flow and pressure of a surface pump?
- Pressure: this characteristic represents the force of the water at the discharge point as a function of pipe cross-section; pressure is expressed in B (bars). Many manufacturers also give pressure in CMW (column metres of water), where 1 B = 10 CMW. Pressure goes hand in hand with flow. This is a central law of hydraulics: for a fixed flow, a pump pipe of great section will produce little pressure relative to a pipe of smaller section.
- Example: A surface pump rated by the manufacturer with a working pressure (at the pump outlet) of 6 B or 60 CMW, has a maximum discharge height of 60m.
- The length of the pump hose is also important, since you'll get a 10% pressure drop, i.e. 1 bar for 10 meters, assuming a 1" or 26mm pipe. To be on the safe side, add 2 B of pressure to the outlet of the pump hose.
- Discharge height is expressed in CMW, or column metres of water. This is important to pay attention to, so you can ensure that the water you pump can reach the evacuation point. Most surface pump manufacturers report either a discharge height (elevation difference between pump body and discharge point) or a TMH value (total manometric height, or 'head') in metres. TMH represents discharge height + pressure at discharge point + intervening pressure drops.
- Flow rate expresses the amount of water pumped in a certain time. You can assume that 6m3/h corresponds to 100 l/min. However, bear in mind that flow rate for a given pump will vary depending on suction depth and discharge height. For a given diameter of pump pipe, the same surface pump will produce a lower flow, the greater the difference in height. Conversely, the closer your suction and discharge points in height, the higher the flow rate. If your surface pump is intended to supply your home, allow a minimum of 2m3/h at the discharge point for a family of five. Then add 0.250m3/h per additional person. If your pump is to be used for watering, 1m3/h is sufficient for 400m² of garden area and 3.5m3/h for 800m². (Contribution by Jeremy, editor for ManoMano).
Surface pumps: clear, charged or highly charged water?
If you're pumping water from a well or a water hole with your surface pump, be careful - the type of water is a factor that shouldn't be neglected.
Water pumped by a surface pump will fall into one of three categories:
- Clear water;
- Loaded water;
- Highly charged water.
If you want to transport wastewater, choose a "loaded water" model. Granular passage is generally around 10-20mm.
Highly charged water
For highly charged waters, you'll find specific surface pumps with a large granular passage (> 25mm). In addition, if you plan on pumping highly charged wastewater, you can get surface pumps equipped with a very large granular passage shredder. (Contribution by Jeremy, editor for ManoMano).
Other important characteristics when choosing a surface pump?
- Monocellular pumps only have one impeller to create suction. These are surface pumps for light household use - such as emptying pools, watering vegetable plots, etc. Monocellular pumps can only be used for clear water with particles not exceeding 0.5mm. A suction strainer is therefore essential. These pumps are noisy, reaching up to 80decibels (dB).
- Multicellular pumps have more than one impeller. Their mode of operation is simple: the first impeller puts the water under a certain level of pressure, the next one increases it and so on. Multicellular pumps are more efficient, economical and robust and also quietier. Multicellular surface pumps are ideal for vegetable plots and open spaces. Also recommended for pumping clear water.
- Centrifugal pumps are simple, robust and offer a high flow rate. These pumps are not self-priming (so a non-return valve is necessary) and can't pump viscous liquids.
- Type of power supply to your surface pump can be single- or three-phase.
- Pump motors are automatically cooled by the water passing through them.
- The operating limit of a surface pump should preferably never be reached. For more information, consult the technical documentation of your pump - which should give a performance curve.
- A stainless steel pump body is the best option, while a cast aluminium motor offers excellent durability.
- Rotor material can vary, although again stainless steel is the top of the range; as for the motor shaft, a carbon alloy is a high quality option, as is stainless steel.
- Automatic priming offers a significant benefit in terms of ease of use.
- A no-water failsafe automatically stops the surface pump in the absence of a water supply.
- With regard to power supply, make sure that the electrical network it's connected to has thermal protection. If it doesn't, and the impeller stops or the pump stalls, you'll burn out the motor!
- To prevent unexpected leaks with whatever type of surface pump, always consider fitting a non-return valve to your system.
Decibel level can be a deciding factor, depending on the location of your pump - to remind you, the health warning threshold is set at 85dB.
Six characteristics for choosing the right surface pump?
- Discharge height;
- Suction depth - beyond 7m you're better off with asubmersible pump;
- Desired flow rate and pressure, factoring in pressure drops - estimate your needs by considering discharge height, suction height, pipe length, and a margin of error;
- Head or HMT - factoring in discharge height, pressure at discharge point and pressure drops;
- Type of water to be pumped - whatever the type, a suction strainer is essential;
- If using for your household water supply, it's advisable to add a booster pump and a bladder tank to take the pressure off your surface pump.
Learn more about household water installations...
How to choose your rainwater collector?
How to choose your watering programmer?
How to choose your booster pump?
How to choose your lifting station?
How to choose your heat pump?
How to choose your garden hose?
How to choose your garden hose fittings?
How to choose your manual pump?
How to choose your watering controller and timer?
How to control your water pressure?
How to choose your water shut-off valve?
Sebastian, self-taught DIY-er, Exeter 187 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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