Sprinkler Irrigation
Calculator for
 Precipitation rate / Nozzle discharge
 Lateral, Manifold, or Mainline Pipe Friction Loss and Velocity
 Pump Brake Horsepower, Water Hammer Surge Pressure
Formulas
and Conversions (PDF: 73 KB)
Instructions:
1. Click on the window and the drop down list of calculations appear.
2. Choose which solution is desired.
3. Enter values for each prompted input. For lateral or manifold calculations,
enter the sprinkler or lateral outlet flows respectively.
NOTE: For repeat calculations, choose Reset
first.
4. The answer displays in the right window when finished. Additional
calculations will display in the window below.
5. Use reference charts for pipe inside diameter, and nozzle fraction
/ decimal sizes.
Example:
A five acre vineyard requires .11
inches per hour precipitation rate for frost protection. The sprinklers
are to be spaced 42 feet down the lateral and the laterals are
48 feet apart. The operating pressure of the sprinklers is 45
psi. There are 23 sprinklers on each lateral and there are 5 laterals
on the manifold pipe. The pressure loss is not to exceed 5 psi
on each lateral, 3 psi on the manifold, and 4 psi on the mainline.
The field is flat. The laterals, manifold, and mainline will be
Class 125 PVC. The water source is located 1000 feet from the
edge of the field. The estimated Total Dynamic Head is 150 feet.
The pump efficiency is 75%.

The Required
Sprinkler Flow is 2.3 gpm

The Required
Nozzle Diameter is .109" (Use 7/64" nozzle from
Nozzle Size chart)

The required Lateral
Diameter is 2.21" (Use 2", from Pipe ID Chart
= 2.229")

The lateral flow
is 2.3 * 23 = 52.9 gpm. The required Manifold Diameter
is 3.55". By selecting a 4" pipe the actual Manifold
Pressure Loss is 1.28 psi.

The total flow of
the system is 52.9 * 5 = 265 gpm. The required Mainline Diameter
is 5.266". By selecting a 6" pipe the actual Mainline
Pressure Loss is 1.78 psi and the pipe velocity is 2.8 fps.

The Pump Brake
Horsepower Required is 13.4 hp.

The Maximum Water
Hammer Surge Pressure with a sudden valve closure for the
mainline pipe is 36 psi for an instantaneous velocity change
of 2.8 fps. and SDR 32.5 pipe. This is additional pressure to
the system pressure. If the highest system pressure is 60 psi
then the total pressure during surge conditions is 60 + 36 =
96 psi.
