Technical Guide · RC Drilling

Reverse Circulation Drilling Rigs: RC350 vs RC500 for Exploration Drilling

By Windrilling Technical Team · August 2026 · 9 min read

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Four years ago I stood at a gold exploration camp in West Africa watching a crew lose samples. The DTH rig drilled fine. The problem was what came up the hole. Rock flour from the walls kept mixing with the cuttings from the bit face, and the lab kept sending back results the geologist did not trust. He threw away more meters than he banked.

Then we swapped the program to a reverse circulation rig with dual-wall rods and a cyclone collector. The next batch of samples was clean enough to assay on site. The geologist stopped arguing with the drillers. The rig paid for the switch inside one season.

RC drilling rigs look similar to DTH rigs from across the yard. They are not the same machine. This guide covers what reverse circulation actually changes, the two rigs we build — the WD-RC350 and the WD-RC500 — and how to pick between them without overpaying.

1. What Is an RC Drilling Rig?

An RC rig — reverse circulation drilling rig — uses double-wall drill pipes. Compressed air goes down the annulus between the two walls and lifts cuttings up through the inner tube. Nothing falls back into the hole. The sample stays in order, depth by depth, and a cyclone collector catches it at surface.

That is the whole trick. Conventional drilling lets cuttings travel up the open hole, where wall rock and old material contaminate them. RC keeps the sample path sealed. For exploration programs that live or die by assay quality, that difference is worth more than any spec sheet number.

On our machines, mast lifting, rod handling, rotation, feed, outriggers and tracks are all hydraulic. The operator controls a full cycle from one seat. A movable slide locks the mast against the ground for rigidity — important when you are pounding through weathered rock in 40-degree heat.

2. RC vs DTH: When Reverse Circulation Wins

A DTH rig is faster in hard rock if all you need is a hole. An RC rig wins when the hole is for sampling, deep exploration or high-volume production drilling. Three situations decide it:

• Sample quality matters. Mineral exploration, geotechnical investigation and ore-body definition need uncontaminated cuttings. RC delivers them hole by hole.
• The hole is deep. In loose or collapsing ground, RC keeps cuttings moving through the inner tube instead of packing the annulus. That is why RC rigs hold speed at 200–500 m where DTH slows down.
• You want dry, continuous samples. No water circulation means no mud to manage and no sample dilution at the lab.

If your job is blasting holes or water wells, a standard DTH rig is usually the right call. If your job is finding out what is in the ground, that is an RC conversation.

3. WD-RC350: The 350-Meter Workhorse

The WD-RC350 is our most requested RC machine. It drills to 350 m with a 105–400 mm hole range, driven by a 129 kW Weichai engine. Rotation torque runs 6,000–10,000 N·m at 40–160 rpm, which covers the medium-to-high pressure hammers we pair with the RC system.

It takes 76, 89 or 102 mm rods in 1.5 or 3 m lengths. The mast stroke is 3.3 m, lifting force 260 kN and feed force 130 kN. At 8 tonnes on tracks with a 25-degree climb, it moves between collars on rough exploration grids without a truck every time.

The RC350 suits exploration teams, geological survey units and contractors running 150–350 m programs on medium terrain. It is the machine I recommend first when someone is new to RC — forgiving to operate, easy to transport, and matched to a 17–42 m³/min compressor package.

4. WD-RC500: Built for Deeper Programs

When the target sits below 350 m, step up to the WD-RC500. It drills to 500 m with a 140–400 mm hole range and carries a 132 kW Cummins power unit — the kind of engine exploration contractors already know and can service in most countries.

The wider hole range matters on brownfield projects where you re-drill old collars or open the hole for casing. Deeper programs also need bigger air. We match the RC500 with higher-capacity compressors so the inner tube keeps lifting cuttings at 400 m plus — the point where underfed air turns a good rig into a slow one.

Both rigs ship as a complete package — rods, hammers, bits, compressor and spare parts — so the sampling program starts the week the container lands, not a month after.

5. RC350 vs RC500: Side-by-Side

Specification	WD-RC350	WD-RC500
Drilling depth	350 m	500 m
Hole diameter	105–400 mm	140–400 mm
Engine	Weichai 129 kW	Cummins 132 kW
Rotation torque	6,000–10,000 N·m	Higher capacity, deep-hole rated
Drill rods	76 / 89 / 102 mm × 1.5 / 3 m	Matched to deep RC strings
Best for	150–350 m exploration, survey, geotech	350–500 m exploration and brownfield
Transport weight	8 t	Heavier, full-size crawler

These are starting points. Tell us your target depth, hole size and site access and we will confirm which model fits — plus the compressor package to keep the samples flowing.

6. Air and Sampling: The Cyclone Matters

An RC rig is only as good as its air system. Working pressure of 1.7–3.5 MPa and 17–42 m³/min airflow is the practical range for the RC350. Underfeed it and cuttings slow to a crawl in the inner tube; overfeed it and you are burning fuel and wearing the cyclone for nothing.

The cyclone collector deserves its own line in your budget. It separates rock flour from the air stream so samples arrive dry and in sequence. A good collector also keeps dust off the crew — most of our customers add the optional dust hood for dry seasons.

Ask three questions before you order: what pressure does the hammer actually need, what air does the deepest hole demand, and is the compressor matched to both? We answer all three on every quote — see the full drilling rig range and matching tools.

7. Checklist Before You Order an RC Rig

• Confirm target depth and hole diameter — they pick the model before anything else.
• Check the assay plan. If samples go to a lab, RC is not optional, it is the method.
• Match the compressor to the hammer and the deepest hole, with 15–20 percent reserve.
• Order rods, hammers, bits and spares together. RC consumables are specialized; do not shop them separately in the field.
• Ask about training and documentation. RC operation is a skill, not a guess — our team provides commissioning support on site.
• See the RC350 and RC500 product pages for full details, or browse all drilling rigs.

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FAQ

Is an RC drilling rig more expensive than a DTH rig?

A comparable RC machine costs more than a bare DTH rig because of the dual-wall rods, cyclone and sampling system. But the cost per meter of usable sample is usually lower — you stop re-drilling contaminated holes. For exploration work, that is the number that matters.

Can an RC rig do normal DTH drilling too?

Yes. With the RC system configured and the right hammer fitted, the rig drills with compressed-air DTH in standard circulation as well. That flexibility is why contractors buy one RC machine for sampling programs and occasional production holes instead of two rigs.

How deep can the WD-RC350 and WD-RC500 drill?

The WD-RC350 is rated to 350 m and the WD-RC500 to 500 m, depending on hole size, ground condition and the air package. Send us your depth, hole diameter and rock type and we will confirm the configuration within 24 hours.