System Design Notes

How to calculate pressure loss in pipes

Pipe length, internal diameter, roughness of the pipe surface, number and type of fittings and orifices, and water temperature all cause friction between the flow medium and the pipe itself. The greater the friction, the more pressure is needed to overcome it in order to maintain the intended flow rate.

Precise calculation of friction loss is usually achieved via software, however in most circumstances an estimation of friction loss will suffice. The charts in this pressure loss nomogram document allows for estimation of friction losses in common pipe diameters. Simply place a ruler  so that it intersects the pipe diameter and desired flow rate (the first 2 vertical scales), the flow velocity and pressure loss resulting will now be indicated where they intersect the ruler. You can now multiply the pressure loss in mbar by the length of pipe.

Note: remember to also add 0.1 bar of pressure loss per m of vertical lift. If the pump is drawing water from beneath by suction, this is much harder for a centifugal pump and reduces pump output capacity by roughly 0.5 bar per vertical metre of suction.

How to increase the efficiency of water pumps

Automatic pumps are designed to supply pressurised water directly to appliances. Remember that the pump will run at full power until there is no more demand for flow to the outlet.

Ideally toilets and header tanks supplied by an automatic pump via a float valve (ballcock) should utilise the more modern diaphragm or ‘quick stop’ type valves. Old style brass float valves will result in the pump spending most of it’s time pumping against an ever decreasing orifice, which is inherently inefficient.

Efficiency and longevity can both be greatly enhanced by the addition of a pressure vessel between the pump and the appliances it is supplying. The larger the vessel the greater the improvement in efficiency.

Electrical design notes for water pump systems

Most of our pumps are supplied with a 1mm flex cable, at a length of 10m. If longer cables are to be used attention must be given to the necessary voltage drop calculations, and the correct cable chosen accordingly.

Electrical junctions, isolators, plugs, and fittings within a water tank, well or other wet area must be suitably protected against water ingress, even if non submerged. The humidity and vapour pressure inside a tank turret are constant, and far exceed the conditions faced by ordinary outdoor enclosures.

Float switches are intended to switch electrical loads near the appliance. Switching of loads over long cable runs can can be problematic due the the limited size of the cable supplying most float switches. It is therefore recommended that a relay or contactor be used to switch the load at the point of supply.

During startup, inrush current often exceeds 5x the rated current draw of the pump, designs for off grid use systems must take this into account. Additionally a typical power factor of 0.9 should be considered.

Incorrect phase rotation of 3 phase pumps will of course result in their running backwards.

Overcurrent and Residual Current Protection should be used to supply any pump system, ideally on a separate circuit.  We recommend Type C overcurrent and 30mA residual current protection. An RCD trip is usually indicative of a phase to earth fault (see our troubleshooting guide). Circuit protective conductors (earth) must be connected and verified throughout any pump installation (submerged plastic tanks are effectively insulated pools, with no natural fault path to ground). Remember that outdoor tank and pump installations should be inspected with only correctly rated test equipment due to their position outside of the building envelope.

Useful tables and conversion data

Reduction of capacity with temperature
Temperature 0CHead Loss mwc (metres water column)


Reduction of capacity with altitude
Altitude (m)Head Loss mwc (metres water column)


Pressure Conversions
BarMetres waterKilopascal (kPa)Megapascal (mPa)Pounds per square inch (psi)


Volumetric Flow Rate
Litres/second (l/s)Litres/minute (l/m)Cubic metres per hour (m3/hr)Cubic feet per minute (CFM)Gallons per minute (imperial) (GPM)

Ingress Protection Ratings (IP Ratings) Guide

The declared IP rating of a product demonstrates compliance with the standards on this page. Please note the limited time duration of tests below IP68. The suitability of devices with protection level below IP68 for outdoor installation will vary depending on exposure and installed location.

Devices and connections installed within tank turrets or in drainage systems (permanent condensing humidity) should be IP68 or higher, the same as for continuous immersion.

All submerged devices may be  immersed only within the limits stated by the manufacturer.

Ingress Protection Ratings (IP Ratings) Guide
1st DigitDefinitionTest Requirement2nd DigitDefinitionTest Requirement
 0 No Protection None0No Protection None
 1Any large surface of the body, such as the back of a hand, but no protection against deliberate contact with a body part>50 mm1Dripping water (vertically falling drops) shall have no harmful effect.Test duration: 10 minutes

Water equivalent to 1 mm rainfall per minute

 2Fingers or similar objects>12.5 mm2Vertically dripping water shall have no harmful effect when the enclosure is tilted at an angle up to 15° from its normal position.Test duration: 10 minutes

Water equivalent to 3 mm rainfall per minute

 3Tools, thick wires, etc.>2.5 mm3Water falling as a spray at any angle up to 60° from the vertical shall have no harmful effect.est duration: 5 minutes

Water volume: 0.7 litres per minute
Pressure: 50–150 kPa

4Most wires, slender screws, ants etc.>1 mm4Water splashing against the enclosure from any direction shall have no harmful effect.Test duration: 5 minutes

Water volume: 10 litres per minute
Pressure: 50–150 kPa

 5Ingress of dust is not entirely prevented, but it must not enter in sufficient quantity to interfere with the satisfactory operation of the equipment.Dust protected5Water projected by a nozzle (6.3 mm) against enclosure from any direction shall have no harmful effects.Test duration: at least 3 minutes

Water volume: 12.5 litres per minute
Pressure: 30 kPa at distance of 3 m

 6No ingress of dust; complete protection against contact (dust tight)Dust tight6Water projected in powerful jets (12.5 mm nozzle) against the enclosure from any direction shall have no harmful effects.Test duration: at least 3 minutes

Water volume: 100 litres per minute
Pressure: 100 kPa at distance of 3 m

6KWater projected in powerful jets (6.3 mm nozzle) against the enclosure from any direction, under elevated pressure, shall have no harmful effects.Test duration: at least 3 minutes

Water volume: 75 litres per minute
Pressure: 1000 kPa at distance of 3 m

7Ingress of water in harmful quantity shall not be possible when the enclosure is immersed in water under defined conditions of pressure and time (up to 1 m of submersion).Test duration: 30 minutes

Tested with the lowest point of the enclosure 1000 mm below the surface of the water, or the highest point 150 mm below the surface, whichever is deeper.

8The equipment is suitable for continuous immersion in water under conditions which shall be specified by the manufacturer. However, with certain types of equipment, it can mean that water can enter but only in such a manner that it produces no harmful effects.Test duration: continuous immersion in water

Depth specified by manufacturer, generally up to 3 m

9KProtected against close-range high pressure, high temperature spray downs.Test duration:

Water volume: 14–16 litres per minute
Pressure: [8000–10000 kPa / 80–100 Bar] at distance of 0.1–0.15 m
Water temperature: 80 °C

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