5.2 System Pressure Uniformity

As you have learned previously, water pressure determines the amount of water that discharges from the nozzle, in the case of overhead sprinklers or hand irrigations, and from regular drip irrigation emitters.
  • Pressure also influences the pattern of application which determines uniformity for overhead sprinklers.

Non-uniform operating pressures for sprinklers or emitters in a management unit can be a problem. The expansion of the irrigation system beyond the design capacity of the pipeline may mean higher water velocities and larger friction losses.

The result is variation in pressure from end of the system to the other. Watch for signs of an old irrigation setup being added onto during production expansion. Checking the water pressure in the system is a measure/test of system application uniformity. The water pressure in a lateral should not vary more than 20 percent from beginning to the end. Also, the average lateral pressure should not vary more than plus or minus 10 percent (for same results). These are allowable design limits so more variation is undesirable. Application uniformity for overhead sprinklers is not perfect but more pressure variation means even more non-uniformity in application.

Checking system pressure uniformity requires a portable pressure gauge that can be attached to a nozzle for field inspection of pressure. Look for usable pressure gauges. Ask the irrigation manager about the system pressure and how it is monitored.

Unfortunately, few pressure gauges are found on most irrigation systems. The pressure gauge is the most common and practical device for monitoring the system functionality.

A pressure gauge is recommended at the pump, on both sides of a main filter if one exists, and on the main line in the field. These pressure gauges should be monitored regularly to see if the system is operating properly.