Systems Guide - Design
- Size Limitations
Pressure variations occur in all systems. Two factors affect pressure:
elevation and friction. Elevation can add to the pressure if the tubing
is running downhill or reduce it, if the tubing is running uphill. If
the highest point in the system is not more than 10 vertical feet above
the control valve, and pressure compensating emitters are used, then
the pressure difference is within the acceptable range. With friction,
pressure is always lost as water travels through the tubing. Friction
is greater at high flow rates and in smaller diameter tubing.
Tubing should be sized properly to keep pressure loss due to friction
within acceptable limits, while keeping the cost of the system down.
There are many different sizes of polyethylene hose. The most common,
however, is 1/2” (15 mm) which is used mainly as the supply line
and can handle flow rates up to 200 GPH (or less than 3.5 GPM). 1/4”
(4 mm) tubing is usually used to branch off the supply hose to carry
water to any area that is too hard to reach with the supply hose. Because
of its small size, it should not be asked to handle more than 8 GPH
(or (8) 1 GPH emitters).
Most drip irrigation systems require little in the way of design beyond
the most practical or aesthetic considerations. Remember that you can
add to a system if flow rates allow. If not, dividing the system into
two or more sections is also relatively simple. No matter how large
or small your system is, the scale drawing is crucial in determining