Setting Up Sprinklers: How To Find the Pressure and Flow Rate at Your House

Mon, 04/02/2018 - 1:02pm
The spray of a Big Sprinkler in a large backyard behind the shop with trees and a red tractor

Two of the most important pieces of information to know when researching and purchasing sprinklers and hoses are the water pressure and the flow rate at your spigot.

The specifications for sprinklers explain how much pressure you’ll need to run it properly, as well as at what flow rate. While finding these numbers is more difficult when using a large hose or if you’re using a high-powered pump, it’s easy when you’re using a garden hose.

Finding the Pressure or PSI

To find out what the pressure–or pounds per square inch of force (PSI)–of the water in your home, you’ll need to buy a pressure gauge. This gadget screws onto the outlet of your spigot and measures the static pressure, or the amount of pressure when no water is being used.

*Note - The static pressure in your calculation is used as a general guide due to the variables that change water pressure between the water meter and the spigot. Your final pressure at the sprinkler can be less then what you calculate when using your static pressure number.

Finding the Flow Rate or GPM

To find out your flow rate or gallons per minute (gpm), you can use a flow meter or you will need to perform a five-gallon bucket test from the spigot you plan on connecting the garden hose and sprinkler to.

To perform the five-gallon bucket test, you place the five-gallon bucket beneath the flow of water and time it while it fills up. You will need to know the total number of seconds it took to fill the bucket. Once you have that number, you will use the equation below to determine your gpm.

  • Equation: 5 (gallons)/number of seconds to fill, then multiply your answer by 60 to get gpm.
  • Example: It takes you 30 seconds to fill a five-gallon bucket; 5/40 = 0.167, 0.167 x 60 = 10 gpm

Once you know the static pressure and total gpm available from your spigot, you’ll need to calculate the friction loss you can expect. Friction loss will depend on the diameter and length of your hose and how many gpm is flowing through it. You can use the friction loss chart in the FAQ section to find the total loss due to friction and subtract it from your static pressure number

Lastly, changes in elevation also affect the water pressure. For every 10 feet of elevation change, you’ll need to add or subtract 4.33 psi. When going downhill, you add 4.33 psi to your final number, but if you’re going uphill from the spigot to the sprinkler, you must subtract 4.33 psi from your final number.

  • Equation: Static pressure – friction loss +/-- change in elevation = psi available to sprinkler
  • Example: You measure your static pressure at 65 psi and your total flow rate from your spigot at 10 gpm. The sprinkler cart will be connected to 100’ of 3/4" garden hose going down a hill which sits 10’ below the level of your spigot. The nozzle on your big sprinkler can handle all 10 gpm of water that is supplied from your spigot and needs at least 44 psi for the water to spray a certain distance.
    • Static Pressure = 65 psi
    • Friction Loss = -13.77psi/ 100’ of ¾” hose (Found from Friction loss table)
    • 10’ Elevation change downhill = +4.33 psi gained
    • Final psi at the sprinkler calculation 65 – 13.77 + 4.33 = 55.5 psi

Finding the Sprinkler that Works for You

We have the products and expertise you need when you’re ready to invest in a dependable, long-lasting irrigation solution. Spend some time researching what Big Sprinkler has to offer on our website, and contact us if you have any questions the website hasn’t answered. We look forward to answering your irrigation needs.