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Skipping the flush and installing new seals into a contaminated circuit is the second most expensive mistake in rock drill maintenance — second only to not changing the seals at all. The contamination that caused the previous seal failure doesn't disappear when the worn seal is removed. It stays in the circuit: metallic particles from the scored bore, degraded oil oxidation products coating the gallery walls, and micro-abrasives suspended in the oil that the filter didn't capture because they were below its nominal rating. New seals go into that environment and begin degrading on the first pressurization.
Quantifying the cost: a clean-circuit seal installation in an RD22U produces 400–440 hours of service life under standard conditions. The same seal kit installed without flushing into a circuit with an oil cleanliness level of ISO 18/16/13 produces 180–240 hours of service life. The labor cost of the second teardown at 220 hours equals or exceeds the cost of the 45-minute flush that would have prevented it. The flush procedure requires flushing oil at 15–20 L/min through the percussion circuit for 20–30 minutes, with oil temperature between 60–70°C to ensure adequate particle suspension, then draining and refilling before installing the new kit.
Circuit Flush Protocol Before Seal Installation
|
Flush Step |
Method |
Target Result |
Failure If Skipped |
|
Step 1: Drain contaminated oil |
Drain full hydraulic tank and all circuit galleries while warm (60–70°C) |
Remove 90–95% of suspended contamination |
Residual contamination remains active during flush |
|
Step 2: Flush oil circulation |
Run clean VG 46 at 15–20 L/min through percussion circuit for 25–30 minutes |
Oil sample at flush exit reaches ISO 17/15/12 or better |
Insufficient circulation time leaves gallery deposits |
|
Step 3: Filter element replacement |
Replace high-pressure filter and return line filter before refill |
New filter baseline — no bypass from saturated element |
Contaminated filter re-contaminates new oil within 4 hours |
|
Step 4: Oil cleanliness verification |
Pull sample from percussion circuit inlet; send for particle count |
ISO 16/14/11 minimum before proceeding |
Installing seals above ISO 17/15/12 halves service life |
|
Step 5: Accumulator purge |
Purge and refill accumulator gas side; check pre-charge against spec |
N₂ pre-charge within 5 bar of specification |
Low pre-charge creates percussion pressure cycling damaging new seals within 60 hours |
The 45-minute flush and 24-hour oil sample turnaround feel like delays. The 14-hour teardown at 200 hours on a failed installation doesn't feel like anything except expensive. HOVOO supplies circuit flushing procedure guides tailored to RD18U, RD22U, and DD2710 platforms as documentation included with seal kits. Full model references at hovooseal.com.
