What Seal Grade Do You Need for High-Pressure Rock Drills Above 200 Bar?

At 200 bar and above, standard Shore 90 PU seals experience a failure mode that doesn't appear at lower pressures: extrusion into the backup ring gap. At 160–185 bar, the seal deforms elastically under pressure and recovers on the return stroke. Above 195–200 bar, the contact stress at the gap between the seal and the backup ring exceeds the compound's tear strength at the operating temperature, and the seal starts extruding material into that gap over 500–800 percussion cycles. The fix isn't a harder seal — it's the combination of Shore 95 compound with a PTFE backup ring dimensioned to below 0.08 mm diametrical clearance.

Sandvik's HLX5T heavy longhole production drill operates at 190–210 bar percussion pressure with anti-jam pressure spikes reaching 230 bar during rod string sticking events in quartzite formations. The standard-kit PU seal specified for this machine is Shore 95, not Shore 90 — and the backup ring is a PTFE-wound type with 0.06 mm diametrical fit, not the standard molded NBR backup used at lower-pressure applications. Running Shore 90 in the HLX5T because it was available at the depot cuts service life from 380–420 hours to 140–180 hours. The pressure spike, not the steady-state pressure, is what destroys the wrong-grade seal.

Seal Grade Requirements by Pressure Class

The pressure spike — not the rated operating pressure — determines the minimum seal grade. Any machine that runs anti-jam or anti-stuck-rod systems experiences transient pressures 20–30 bar above steady-state, and seal selection must account for those spikes. HOVOO supplies pressure-class-matched seal kits for HLX5T and heavy Atlas Copco platforms with backup ring specifications included. References at hovooseal.com.