Table of Contents
FLOW and PRESSURE
The most often confused terms in the irrigation industry! Whether you are a full-time irrigator, landscaper, plumber, pool and pond installer or gardener, it is very important to know the difference between water flow and water pressure.
What are the differences? How do you accurately measure flow and pressure? Why is it so important?
FLOW
This is the amount of liquid moved in a specified duration of time. This can be expressed in litres per minute (LPM), litres per second (L/S), cubic metres per hour (m3/h) and litres per hour (LPH).
For irrigation purposes, most flows are converted to LPM. eg: 2 L/S = 120LPM, or 3m3/h (3000LPH) = 50LPM.
To find out the flow rate of a tap, follow these simple steps: remove any tap fittings, open the tap fully, insert a bucket underneath the open tap, time how long it takes to fill the bucket. This is what is referred to as a “Bucket Test”. Therefore, if it takes 12 seconds to fill a 9L bucket, the available water flow is 45LPM. (60 seconds ÷ 12 seconds = 5) (5 x 9L bucket = 45LPM)
PRESSURE
This is the force of liquid moved. For every 1m in height, a downward force or pressure of 10kPa (kilopascals) is registered, eg: if a bucket of water is emptied from a height of 1m, the water pressure is 10kPa. If a bucket of water is emptied from a height of 20m, then the water pressure will be 200kPa. Since most irrigation components require pressure to work, the correct amount of pressure needs to be provided by either a tap or pump.
FLOW and PRESSURE
Note an example of some differences between flow and pressure: A 9L bucket of water is emptied from a height of 1m and this takes 1 second – the water flow and pressure is 9L/S @ 10kPa. A 9L bucket of water is emptied from a height of 20m and this takes 20 seconds – the water flow and pressure is 3LPM @ 200kPa. Same bucket of water but at a different height and a different length of time to pour out.
This example shows that FLOW is NOT the same as PRESSURE. A good water flow does not mean good pressure; just the same as good pressure does not mean a good flow of water. Therefore, each tap, pump or water outlet needs to be tested or measured as to the water flow and water pressure available.
MEASURING
An effective way that anyone can measure water flow is by doing a “Bucket Test” as outlined in the FLOW section. To measure the pressure from a tap or pump outlet requires a pressure gauge. Usually, devices with a combined flow meter and pressure tester retail for hundreds of dollars.
However, Hills Irrigation offers an inexpensive compact unit that will test water pressure in combination with doing a “Bucket Test”.
In order to install an irrigation system properly, it needs to be designed with the available flow and pressure rates. This will alleviate problems in sprinkler and nozzle sizing or under-speccing a pump. Properly calculating water flow and pressure will allow you to install the appropriate pressure regulator for drip irrigation systems and other sensitive irrigation set-ups.
SO MAKE SURE YOU ALWAYS COMPLETE AN ACCURATE FLOW AND PRESSURE TEST!
Vince is Managing Director of Hills Irrigation and is supported by Lisa in an administrative capacity. Andrew, Isaac and Megan look after the day to day needs of both online and shop customers. As Project Manager, Vince is also responsible for installation projects along with his team. It is his responsibility to work closely with clients to ensure that scope of work is understood and followed.
