Low-Temp Damping Piston of Atlas Copco RD22U in Norway

Norway's underground hydropower construction—the ongoing expansion of pumped-storage projects in Hardanger and Vestland, plus the deep road tunnels through the Scandinavian mountain range—operates RD22U drifters in a specific cold-water challenge that surface operations don't face. Hydropower adit drilling runs in rock saturated with snowmelt groundwater at 2–5°C year-round. The flushing circuit carries water at 3–4°C into the drill face; that water contacts the front housing assembly and cools the shank zone to temperatures that affect the damping piston's hydraulic circuit performance even in summer months, when the surface temperature is 20°C.

The damping piston in the RD22U absorbs the tensile stress wave reflected from the rock face after each percussion blow. Its hydraulic circuit controls how quickly the damping cylinder returns after each wave absorption event—the timing is set by calibrated orifice flow through hydraulic oil. When that oil is cold and viscous, the return rate is slower than designed, the damping system doesn't reset fully before the next percussion cycle arrives, and the damping efficiency drops progressively through the early minutes of a drilling shift until oil temperature stabilizes.

Cold-Water Flushing Effect on RD22U Damping Piston Circuit

Norwegian hydropower tunnel contractors have established a cold-start protocol: 10 minutes at 60% percussion pressure before stepping to full rate, allowing the damping circuit oil to warm through the partial-load phase. The protocol also includes checking damping piston seal condition at every 400-hour service—cold cycling accelerates NBR seal stiffening incrementally, and a stiffened damping seal reduces the piston's range of motion before it becomes a visible failure. HOVOO supplies RD22U damping piston seal kits with cold-temperature validated compounds for Norwegian and Nordic hydropower tunneling operations. References at hovooseal.com.