A relationship formed in mid-1996 has led to Fulton Hogan becoming the leader in variable application telescopic bitumen sprayers for the past quarter of a century.

Fulton Hogan’s Engineering Projects Manager Darryl Evans (pictured left) and NZ Mechanical Engineer Richard Shaw (far right) were involved at the start, and are still refining a system widely regarded as world leading.

Working with computerised machine control company Gregor Electrical (now Swarm Intelligence), their sprayers have changed the way much of New Zealand’s 96,000 km of roads are sealed. Darryl and Richard are shown with their Swarm Intelligence’s Craig Blaikie and Pat Adair.

The Multispray® technology makes chip seal application more accurate, with less waste, more uniform and resilient. It achieves this by accounting for the difference between a typical road’s surface at the shoulder, at the first wheel track, the ‘drip line’ (between the wheel tracks), the other wheel track and the road centre.

They first designed and fabricated a two-piece ‘telescopic’ spray bar with two rows of jets, each with different flow rates. By pioneering a means of having the two rows work in tandem, application rates from 70 percent to more than 100 percent could be applied on any part of the road.

To automatically control the on/off operation of each of the 100 spray jets, the team developed a PLC based control system with touchscreen computer interface (MMI or Man Machine Interface) for the operator to configure the system for each spray run.

The objective was for the operator to simply follow the existing wheel tracks on a road and extend (or retract) the spray bars as much as the road required, with the combination of spray jets automatically adjusting the differential spray rates.

Because PCs at the time were fragile, the first hard-drive was suspended on springs in the truck cab to prevent it being shaken senseless. Any remote communication between the sprayer control system and Swarm Intelligence’s nerve centre was by plugging cables into commandeered fax lines. Remember them?

The team has since pioneered an expandable seven metre sprayer, rather than the industry standard five metres. Believed to be unique in the world, it consists of two 3.5 metre extending spray bars that retract to no more than the width of the truck when it is not in ‘over width’ mode.

A proportional drive system for the spraybars was recently added to improve the quality of edge line finishes.

“Previously the quality of the finish was a bit ‘zig zaggy’,” says Darryl. “Now the operator is able to control the bar speed exactly as required.”