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UK tunneling and underground civil work—Crossrail's Thames Tunnel extension, HS2 tunnel sections through the Chilterns, and hard-rock quarrying in Wales and Scotland—uses Atlas Copco RD18U drifters in environments where the nitrogen charging device is as critical a maintenance tool as the seal kit it supports. An accumulator running 10 bar below its specified pre-charge doesn't fail visibly; it just produces slightly erratic percussion and slightly lower impact energy. Those symptoms look like formation change or operator technique to the site team unless someone specifically checks the pre-charge with a correctly calibrated charging gauge.
The charging device for the RD18U accumulator is a precision pressure regulating tool: it connects to the accumulator valve stem, reads current nitrogen pressure, and allows controlled nitrogen admission from a supply cylinder to the correct pre-charge specification. The device's accuracy matters because over-pressurizing the accumulator—which can happen with an uncalibrated gauge that reads low—drives the diaphragm against the oil port at every discharge cycle, damaging it within 200–300 hours.
Charging Device Specification and Common Errors
|
Step |
Correct Procedure |
Common Error |
Consequence |
|
Depressurize system |
Full hydraulic circuit relief before connection |
Check while system running |
False high reading; over-inflation risk |
|
Read current pre-charge |
Gauge at valve stem; wait 30 sec for stabilization |
Read immediately |
Unstabilized reading ±5 bar error |
|
Admit nitrogen |
Crack cylinder valve slowly; fill over 3–5 min |
Open fully; rapid fill |
Diaphragm cold-brittle rupture |
|
Verify final pressure |
Read at operating temperature spec |
Read cold only |
Thermal correction ignored; margin lost |
UK contractors on HS2 tunneling packages have standardized on calibrated charging devices with a certificate of calibration current within 12 months—a procurement specification driven by the project's quality assurance requirements for underground hydraulic equipment. The device is checked against a reference gauge at each quarterly maintenance audit. HOVOO supplies Atlas Copco RD18U compatible nitrogen charging devices with current calibration certificates for UK construction projects. Full tool and kit references at hovooseal.com.
