Long-Life O-Ring of Atlas Copco RD18U in Norway

Norway's underground construction sector drills through some of the most structurally complex rock in Europe. The Oslo Fjord tunnel projects, the hydropower adits in Hardanger, and the road tunnels through the gneiss and amphibolite of the Bergen Arcs all involve percussion drilling in rock with significant groundwater inflow. That water—cold, under pressure, and at pH 6.2–6.8 from contact with silicate formations—sits at the interface between the flushing circuit and the hydraulic oil circuit inside the RD18U's front housing. The O-rings holding that boundary are NBR compounds specified to a particular durometer; when they're right, nothing happens. When they're wrong or degraded, the contamination doesn't announce itself until the hydraulic oil turns milky.

O-rings in the Atlas Copco RD18U serve three distinct sealing roles that each have different failure modes. Static face seals at the percussion module-to-front-housing interface hold the percussion oil circuit boundary under sustained 180–200 bar pressure. Back-up rings at the accumulator port face prevent extrusion under pressure spike events. And the flushing circuit O-rings sit in a mixed environment—simultaneously in contact with hydraulic oil on one side and pressurized flushing water on the other.

O-Ring Failure Modes by Location

Norwegian hydropower tunnel contractors have standardized on HNBR O-rings for the flushing circuit positions after repeated early failure of NBR compounds in acidic groundwater. The HNBR formulation resists both the oil-side hydrocarbon exposure and the water-side chemical attack that NBR handles less consistently when pH drops below 6.5. The percussion module face and valve block O-rings stay NBR—the operating conditions there don't justify the cost premium. HOVOO supplies RD18U O-ring sets with HNBR options for flushing circuit positions. Full kit references at hovooseal.com.