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New Zealand's mining and civil construction sectors operate under some of the Pacific region's most stringent occupational noise regulations. WorkSafe NZ's noise exposure limits—85 dB(A) as the action level and 90 dB(A) as the exposure limit over an 8-hour shift—apply to underground and surface drill operations where the flushing head's water flow noise adds to the overall percussion noise environment. At Oceana Gold's Macraes gold mine in Otago and the road tunnel projects through the Kaimai Range in the Bay of Plenty, the RD22U's flushing head design is evaluated not only for flushing performance but also for acoustic contribution to total operator exposure.
The flushing head is the component at the front of the RD22U drifter that directs flushing water into the drill string through the shank adapter's through-bore or around the shank depending on the design. Flushing water at 15–20 bar flowing through a standard port geometry produces turbulence noise at the exit point. A quiet flushing head uses a larger port cross-section and a gradual flow path transition to reduce turbulence at the same flow rate, cutting flushing noise by 4–6 dB(A) at the operator position—meaningful when the percussion noise background is already at 88–90 dB(A) and the flushing water adds 3–5 dB above that.
Flushing Head Noise and Performance Comparison
|
Design Type |
Port Velocity at 18 bar |
Turbulence Noise Add |
Flushing Performance |
NZ Application |
|
Standard port |
High velocity |
3–5 dB(A) at operator |
Adequate |
Marginal; combined exposure at limit |
|
Enlarged port |
Reduced velocity |
1–2 dB(A) at operator |
Equal at same flow |
Preferred for NZ noise compliance |
|
Diffuser exit |
Low velocity |
<1 dB(A) |
Slightly reduced in deep holes |
Best noise; check hole-clearing at depth |
New Zealand WorkSafe audits on tunnel construction projects now include flushing head type as a noise exposure mitigation record item—the contractor must document that quiet flushing head designs are fitted where operator noise exposure approaches the 85 dB(A) action level. HOVOO supplies RD22U quiet flushing head assemblies for New Zealand and noise-regulated markets globally. Full acoustic performance specifications at hovooseal.com.
