Sizing your Spot-Spitter Supply Lines for high uniformity:

Good application uniformity is critical for good system performance and plant health. If you put too many Spitters on one supply line you will exceed the supply line’s capacity, resulting in non-uniformity (some containers will get more water than others). Use the Design page to estimate the uniformity of your system before you build it, and make changes if it’s too low. You should aim for uniformity of 90-95% for consistent plant size and health.

Enter the parameters of your system (Spitter color, supply line diameter, etc.) into the Design page. The calculator will warn you if your uniformity is below 90%, or if the flow velocity within the supply line exceeds 8 feet per second (this can damage fittings). It also gives the overall flow rate required per supply line, which you can use to size your zones and submains.

If uniformity is too low you can improve it by: 1) using a lower flow Spitter, 2) using a larger diameter supply line, 3) reducing the number of Spitters on your supply line or 4) reducing the length of your supply line. Try a few different combinations to solve the problem. One possible trick to avoid this compromise is to center-feed your supply line from a Tee fitting, effectively making it into two supply lines that are half the length and have half the number of Spitters.

Sizing your zones:

Size your zones (number of supply lines you run simultaneously) so that the combined flow rates of the supply lines in your zones do not exceed the capacity of your water supply. For example, if the calculator tells you that each supply line requires 10 GPM, and your water supply capacity is 100 GPM, each zone can supply up to 10 supply lines.

Sizing your submains:

Finally, your submains (large PVC pipes that feed your supply lines) must be large enough to supply all of the supply lines attached to them. Choose a diameter that results in submain flow velocity below 8 feet per second for good performance. You can calculate flow velocity as

V = .408 x Q/d2

In this equation, Q is the total flow rate through the submain (supply line flow rate times the number of supply lines) and d is the submain diameter. For example, if you simultaneously run 10 supply lines on one submain Q is 100 GPM. If your submain is 2” PVC, d is 2 so V = .408×100/22 = 10 feet per second, which is too high. Upsizing to a 3” submain results in 4.5 fps which will work well. Remember that if your supply lines are center-fed, each submain takeoff requires the flow rate of two supply lines.