Pumps for Irrigation and Rainwater Harvesting
Pumps For Irrigation And Rainwater Harvesting
Find out how to choose a submersible pump for irrigation and rainwater collection systemswater | shopping | general
is the key component in most irrigation
, rainwater toilet flush
, and greywater
systems. The commonest requirement is to shift volumes of water from a large collection/storage tank to a header tank
from which it is used to water crops or gravity feed toilet cisterns.
Mains Power or Low Voltage Pumps
The first choice to make is whether to purchase a mains powered
pump, or a low voltage
(typically 12V) one.
A 300W mains powered pump draws a current of below 2 Amps and so quite thin cable
can be used - e.g. the cheap 5A-rated twin and earth cable
used in domestic lighting circuits would be perfect. A 300W 12V pump on the other hand would draw a current of over 25 Amps and so thick cable
would be required - very expensive with the price of copper where it is, particularly over long runs. (Visit our Line Losses Calculator
for a rough idea of the diameter of cable required for low voltage pumps).
Pump Cost and Quality
In general a mains powered pump will cost less
than an equivalent low voltage pump for all but the smallest of pumps. There are more mains powered pumps manufactured and sold than low voltage pumps which explains the difference in price
, but low voltage pumps tend to be better made from higher quality materials
than mains powered pumps as they are typically designed to be used in harsher conditions - e.g. outdoors and marine environments.
It is very useful to purchase a pump with a built in float switch
. This will automatically cut the power to the pump when there is no water left to pump thereby protecting the pump from being badly damaged and/or burnt out by running dry
. Mains powered pumps are more likely than low voltage pumps to come with an integrated float switch
- probably because a float switch on a low voltage pump has to switch a high current necessitating either an expensive float switch or added electronics (which can go wrong!). Submersible pumps
are much more likely to have integrated float switches than other pumps.
If using a pump without an integrated float switch, a suitable float switch
) should be fitted to the water tank above
the pump inlet to protect the pump. This will add to the cost and complexity of any pump controller
. (See our articles Automatic Pump Shut Off Circuit
, and Simple Sump Pump Controller
If a pump is to be switched by a relay
then a qualified electrician
must make any high voltage connections. Therefore the cost of an electrician must be deducted from the initial savings of purchasing a mains powered pump. Future maintenance must be also be considered as an electrician could be required again.
Head and Flow Rate
The ability of a pump to pump is given by its head
and flow rate
. The head
is the maximum height to which a pump can pump water.
In the UK most pumps are sold with the head
specified in metres
, or alternatively the water pressure
generated by the pump measured in psi
(pounds per square inch).
To convert from head to psi
pressure (psi) = 0.434 * head (feet)
pressure (psi) = 0.132 * head (metres)
To convert from psi to head
head (feet) = 2.31 * pressure (psi)
head (metres) = 0.705 * pressure (psi)
When selecting a pump
, you need to measure the height difference between the pump's water inlet, and the highest point the water is to be pumped. The head
of the pump chosen must be greater than that measured distance, ideally by at least 25% so the pump is not over-worked.
The flow rate
is a measure (typically in litres or gallons per minute) of the amount of water which can be pushed out of the pump. This flow rate falls when water must be pumped upwards - i.e. a pump with a head of 5 metres and a flow rate of 10 litres per minute, will have a flow rate of 0 litres per minute if the water is to be pumped 5 metres or higher.
For non-submersible pumps, a further measure is lift
. This tells you the maximum difference in height between the pump, and the end of the pipe connected to the pump inlet.
Buying a Pump
A huge range of pumps
are listed for sale on eBay UK
. Click here to search for Submersible Pumps
in the UK (with the 100's of matching results for aquarium and fish pond pumps removed), or here for the same search on eBay USA
In order to protect your pump from multi-switching
- i.e. turning on and off rapidly - have a look at our article Water Pump Hysteresis Circuit
Article Last Modified: 15:16, 19th Aug 2008
Comment on this Article
If you have any comments on this article, please email them to email@example.com
Recommended Related Articles
People who read this article also enjoyed the following articles:Solar Powered Irrigation
Water your garden or allotment with a solar powered irrigation systemArticle Last Modified: 15:58, 12th Jun 2008solar | waterRainwater Toilet Flush System
Find out how to put together a complete rainwater fed toilet flushing systemArticle Last Modified: 15:16, 19th Aug 2008water | general | electronicsFlush Toilet with Rain Water
Flush your toilet with collected rain waterArticle Last Modified: 10:06, 8th Oct 2012water | education | generalDigital Watering Timers and Solenoid Valves
Find out more about automatic watering systems with electronic timers and solenoid valvesArticle Last Modified: 15:58, 12th Jun 2008water