Introducing: Flow Rate
Before you start putting water onto your garden, there are really two things you have to know first. Without knowing these two simple facts, you’re going to
- create problems for your garden
- probably waste water and money
- water inefficiently
- potentially break your irrigation system
So while you likely understand these things, I’m going to suggest you do the tasks and write down the results so you won’t forget them. (I put stuff like this in Evernote)
The numbers you’re going to develop are the backbone of the rest of your system and determine how you apply water.
So What Are These Numbers and Why Are They Important?
The first number is “flow rate”.
How much water does your system pump out? Or, for our test, how long does it take to pump out 5 gallons of water.
Exercise Number 1
- Get a 5-gallon pail. Take it to your outdoor tap.
- Attach your regular hose to the tap. We’re going to do this because the flow rate at the end of the hose will be lower than the flow rate at the tap.
- Put the end of the hose into the bucket.
- Turn on the tap and start timing.
How long does it take to fill a 5-gallon bucket.
- Divide that time by 5. This is your gallon per minute flow rate.
- Multiply that gallon per minute flow rate by 60. This is your gallon per hour flow rate.
Under A Minute For Five Gallons?
One potential issue is if your 5-gallon bucket is filled up in a minute or less. If this happens, your objective changes to discover how much in a second.
- Let’s say you get 5 gallons in 45-seconds.
- This means it takes 5 divided by 45 (5/45 =.1) or .1 gallon per second.
- A minute has 60 seconds. .1 X 60 = 6
- You get 6 gallons in 1 minute.
- Or 6 X 60 = 360 gallons in one hour.
- Your flow rate is 360 gallons per hour.
If you design extra zones so you’re never using the entire flow rate, then being “close” here works well.
Why Is This Important?
When we start designing our irrigation system, each sprinkler or drip emitter will have a flow rate. So if an emitter puts out 1-gallon an hour and you have 15 emitters in a zone, you’re using 15 gallons an hour.
A “zone” is a collection of emitters or sprinklers that all operate at the same time
You know your gallon per hour flow rate from filling up the bucket so you also know how many 1-gallon per hour emitters you can run at the same time.
Let’s say you have an hourly flow rate of 100 gallons per hour but you want to use 150 emitters.
The emitters use 150 gallons of water an hour but you only have 100 gallons of water.
This means you need to create two “zones” of 75 emitters each. Or one of 100 emitters and one of 50 emitters.
In practical terms, you’ll set up a zone for each major area of the garden but you now know you can’t have too many emitters in any zone. You can have fewer than the flow rate in any zone but never more.
If you have 100 gallons an hour flow rate, the maximum you can run is 100 emitters at the same time. There is no minimum number of emitters to a zone if you have the flow rate that will handle them. And yes, you can use four zones of 25 emitters to take advantage of your 100 gallon flow rate or 10 zones of 10 emitters or…
Bottom line – your emitter output can’t exceed your flow rate.
And that’s why we need to understand our flow rate.