Guide written by:
Sebastian, self-taught DIY-er, Exeter
The surface pump is a great solution for any type of clear water or wastewater pumping. Monocellular or multicellular, the role of the pump is to transport water under pressure. For drawing from a well, watering a garden or simply emptying a pool, a surface pump is a must!
- Flow rate
- Total head
- Supply height
- Discharge height
- Pressure drop
Surface pump: a definition
A surface pumpsucks up water at point A and pumps it out at point B. Point A may be a well, river, pool or garden pond and Point B a garden, hose, wastewater network, ditch, etc. A surface pump can also supply domestic appliances such as washing machines, dishwashers and toilets.
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 submersiblepump 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?
Before you get your strainer working, here are a few pointers and definitions to help you find your way around pressure, discharge height and flow rate!
- 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 dischargeheight (elevation difference between pump body and dischargepoint) 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 aminimum of 2m3/hat the discharge pointfor 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).
If you're drawing water from a well, consider the suction depth and the type of water you're drawing. You'll also need to pay attention to discharge height, i.e. the height between your surface pump and the point where the water is distributed - if your garden is much higher up than the bottom of the well, for instance. If you have an automatic watering system, determine the exact flow you need, because the more watering points, the more water your system will consume!
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 - thetype 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're just looking to use your surface pump for watering from a rainwater collector, a "clear water" model will do just fine. Its granular passage (or granulometry) is very small (< 5mm) - so larger suspended particles will tend to clog and damage the pump body.
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 pumpinghighly 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?
Tips for choosing your 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).
- Multicellularpumps 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.
- Theoperating 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 pumpbody is the best option, while a castaluminiummotor 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?
To get down to basics and choose your surface pump wisely, you need to determine:
- Discharge height;
- Suction depth - beyond 7m you're better off with asubmersiblepump;
- 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.
Consider your needs carefully at the outset, erring on the side of overestimation. If you're drawing well water from a depth of 7-8m, go for a submersiblepump: for one it'll be quieter because it's submerged; two, you'll get better performance. If you don't use your pump in the winter, consider draining and protecting it from frost. Bladdertanks don't always offer great resistance to corrosion, and anti-rust protection is easy to apply and inexpensive, so it's worth considering. Bladder tanks also need to be drained along with the whole system, so don't let yourself get caught out!
Learn more about household water installations...
To find out more about household water installations, follow our editors' advice and check out their other guides:
Guide written by:
Sebastian, self-taught DIY-er, Exeter, 187 guides
Redo a roof with wooden beams? Check.Advise Mister everybody in the DIY shop? Check.Redo the bathroom plumbing? Check.Fit together, build the walls, paint a partition, throw my hammer in a rage thinking that it will fix the problem? Check. 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!