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%.

1. The Required Sprinkler Flow is 2.3 gpm
2. The Required Nozzle Diameter is .109" (Use 7/64" nozzle from Nozzle Size chart)
3. The required Lateral Diameter is 2.21" (Use 2", from Pipe ID Chart = 2.229")
4. 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.
5. 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.
6. The Pump Brake Horsepower Required is 13.4 hp.
7. 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.