Happy Friday!

So you have decided to install an automated sprinkler system. You have also decided that you want to install it yourself. You will need to determine the design capacity of your system for it to work properly. 

Yes, you can do this and have a pretty awesome automated system. How much will you save depends on materials. Also keep in mind that if you hire a professional they will open and close your system. A professional will also likely guarantee their work for some period of time. So there is a lot to consider. 

Steps:

• Measure the static pressure in your water pipes (with a water pressure gauge)
• Determine the size of your water metre (this is usually stamped on your water metre)
• You will need to know the size of your service line

After collecting this information you will be able to determine the design capacity for your sprinkler system by referring to a design manual online. Scott refers to Hunter or Rainbird Design Guides. Using the above information you will be able to determine the maximum water flow rate that you can use for you sprinkler system. However you need to keep the velocity of the water in the pipes below 8 ft/s to avoid damaging the pipes. This will usually be the limiting factor if you are on city water.

Example

Here are the numbers for our house:

• Static Pressure: 70 psi – 482kPa
• Water Meter Size: 5/8″ – 15mm
• Service Line Size: 3/4″ – 19mm – Copper

Using the table below we can determine the working pressure, and the available flow for the sprinkler system.

• Working Pressure: 350kPa – 50 psi
• Available Flow: 30 l/min – 8 gal/min (deducting 7.61 l/min for copper pipe)

However we need to keep in mind that we do not want to exceed 8ft/s of flow in the pipes to prevent damaging them. Using the chart below we can see that a flow of 8 gal/min puts us at a velocity of 5.88 ft/s in our 3/4″ copper pipe service line. Rainbird has drawn the chart with the limit of 5 ft/s which should not be exceeded, however in their own design example they exceed that limit as they declare that it is too restrictive for most systems. They say that 5-7.5 ft/s should not be exceeded. Since we are at 5.88 ft/s we are safe to use this.

• Working Pressure: 350kPa – 50 psi
• Available Flow: 30 l/min – 8 gal/min (deducting 7.61 l/min for copper pipe)
• Water Velocity in 3/4″ pipe – 5.88 ft/s

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