A
well designed feed circuit will ensure all roots are fed and flushed, and
not interrupted by blockages. Aim to make the feed circuit tidy and
uncomplicated. To minimize the risk of leaks and blockages avoid junctions
and restrictive feed outlets (e.g. drippers) and always use filters.
Material selection
Avoid
corrosion problems associated with metal. Plastic components are
generally cheaper, more flexible and readily available and last longer.
Pipes:
Flexible plastic tubing (e.g. polypropylene) is usually appropriate for
all situations and reduces the need for junctions. Its cheapness provides
option of discarding it once it becomes internally contaminated.
Where
junctions are required, push fit fittings (e.g. barbed) are common (Fig
6.15). These are quick and easy to install. At high pressures however
they are prone to leaks and therefore require securing with clamps (Fig
6.16).
Rigid
plastic pipes (e.g. PVC) can be preferable for the ‘primary’ circuit.
However, the white variety is not opaque and inside walls are prone to
algal growth. These
generally require glued junctions, and although permanent, are resistant
to leaks. Note, rigid plastics (e.g. PVC) are relatively brittle and
therefore inappropriate for high traffic areas.
Maximizing flow rate
+ Pipe diameter: Use large
diameter pipes. Do not underestimate the degree to which small diameter
pipes reduce flow rates, especially as the length of the pipe increases.
Small diameter pipes are also more prone to blockages from salt build-up,
dirt, algae, plant matter, etc.
+ Elbows (or tees): These also
reduce flow rate (and increase the risk of blockages). In many situations,
these can be avoided by using ‘flexible’ instead of ‘rigid’ pipes.
Equilibrating outlet flow rates
To achieve equal flow rates from multiple
outlets (often necessary for run-to-waste systems), use the following
principles:
1. Use maximum diameter piping for the
primary circuit.
2. Pipes joining the primary circuit to
the feed outlets must be of equal length and diameter. However, using
wider pipe will reduce the need for being consistent with this
requirement. Outlets (e.g. drippers, etc) must be of equal type/
specification. Ensure these components are maintained to avoid partial
blockages (see section below).
3. If “pressure compensating” drippers
are feasible, these will yield a preset flow rate (see “Feed Outlets”).
