Redesign, zone expansion and pressure correction

Re-measure the supply — the number everything else depends on

Static pressure and available flow are measured again rather than taken from the original design. Municipal pressure changes over decades, service lines corrode and lose capacity, and neighbourhood demand shifts.

Watch for: A redesign based on the original as-built figures. If the supply has degraded since installation and nobody re-measured, the new zoning inherits an assumption that is no longer true.

Map what is actually in the ground

Valves are located, zones are traced, and head types and nozzles are inventoried per zone. On a system with years of repairs behind it, this stage routinely finds heads and nozzles that nobody intended to be there.

Watch for: Skipping the trace on the assumption that the as-built drawing is accurate. Repairs are rarely drawn, and a zone map that is a decade out of date makes every downstream calculation wrong.

Recalculate the flow budget and re-zone

Total available flow is divided across zones so that no zone demands more than the supply can deliver at working pressure. Overloaded zones are split; zones whose planting has changed character are separated.

Watch for: A new zone simply teed off an existing one. This is the cheap version and it makes the original problem worse — the parent zone now has even more heads competing for the same flow.

Address pressure at the right level

High pressure is corrected with pressure-regulating heads or stems, or with a regulator at the valve or at the point of connection. Low pressure at the far end is usually a flow problem, not a pressure one, and is solved by reducing what the zone has to feed.

Watch for: A booster pump proposed as the answer to misting. Boosting pressure that is already too high compounds the fault. Establish which of the two problems you have before anyone quotes hardware.

Match precipitation rates within every zone

Every head on a zone should apply water at a comparable rate. That means one head family and matched-rate nozzles per zone, so the zone can be scheduled as a single unit rather than as a compromise.

Watch for: Mixed brands left in place because they still work. A functioning head applying water at a different rate to its neighbours is a permanent uniformity fault, and it is invisible until you measure it.

Extend wiring and valve capacity for what you add

New zones need a valve, a wire path back to the controller, and a free station on it. Where spares were pulled at installation this is straightforward; where they were not, the wire run is often the largest single cost of adding a zone.

Watch for: A controller already at its station limit. Discovering this after the trenching is done turns a zone addition into a controller replacement on the same invoice.

Convert bed zones to drip where it makes sense

Redesign is the natural moment to move planted areas off spray and onto drip, because the zone is being reworked anyway. It removes the turf-versus-beds scheduling conflict permanently.

Watch for: Drip teed into a spray zone as a shortcut. Drip and spray apply water at rates that differ by an order of magnitude and must never share a valve, however convenient the pipe run looks.

Re-commission and re-programme everything

After a redesign the whole system is re-run, arcs re-set, and the controller re-programmed — including the zones you did not change, since their share of the flow budget has moved.

Watch for: Only the new zones being programmed. Re-zoning changes the hydraulics for existing zones too, and leaving their old run times in place undoes part of what you paid for.