Air-Leg Rock Drilling in Narrow Tunnels: Feed Setup, Air Supply, and Water Flushing

Direct answer: air-leg rock drilling can be a practical method for narrow underground drifts and small tunnel headings, but the drilling setup must be planned around the available working envelope rather than the rock-drill model alone. The key constraints are the pusher leg’s retracted and extended geometry, collaring position and drilling angle, dynamic air pressure and flow at the face, water-flushing arrangement, hose routing, drill-steel length, bit compatibility, and the space needed to reposition the drill safely.

This guide is for mine-development crews, tunneling contractors, distributors and procurement teams preparing an air-leg drilling package for restricted underground openings. It focuses on application setup and working conditions, not on choosing one model over another. The selected manufacturer’s operating manual, mine procedure and site risk assessment remain controlling.

1. Why Narrow Tunnels Change the Air-Leg Drilling Setup

In a large working area, a drill package can often be positioned around the preferred hole. In a narrow drift, the opposite is true: the walls, back, floor, services and operator clearance constrain where the drill and pusher leg can physically sit. That changes the usable feed angle, the practical drill-steel length, how often the leg must be repositioned, and how hoses can be routed without becoming a handling problem.

Current Atlas Copco underground rock-drill guidance explicitly describes water-flushed, pusher-leg-mounted drills for driving drifts and tunnels with small cross sections. Its current pusher-leg range also shows why geometry matters: different single- and double-telescopic legs can have materially different retracted and extended lengths even when their nominal feed duty is similar.

2. Start with the Working Envelope, Not the Drill Model

Before deciding how the face will be drilled, record the actual space available for the complete setup. The useful dimension is not just tunnel height or width. It is the space required by the rock drill + pusher leg + drill steel + operator position + hoses at the intended collaring point.

A single-telescopic and double-telescopic leg can solve different geometric problems. As one current OEM example, Atlas Copco’s ALF 67/80D double-telescopic leg is designed to provide a long feed from a relatively short retracted package. That does not make it the right leg for every drill; OEM tables also pair particular pusher legs with particular rock drills. The principle for buyers is more important than the model name: leg geometry and drill compatibility must be checked together.

PerfoMax’s current FT160-series air-leg page follows the same discipline: FT160 is treated as a family name rather than proof of universal fit. The complete suffix, collapsed/extended length, feed stroke, mounting interface and approved drill pairing should be confirmed before quotation.

3. Match the Feed Setup to the Hole Direction

The pusher leg has two jobs: support the drill and provide controlled feed force. The correct amount of feed depends on the drilling position, collaring stage, rock response and the selected equipment. Excessive feed can destabilize collaring or load the drill steel unnecessarily; insufficient feed can reduce effective energy transfer and make the drill bounce or drill slowly.

For a narrow heading, the practical sequence is to plan the face around positions the leg can actually support. Avoid treating the pusher leg as a way to force the drill into an unsuitable orientation. Dedicated upward drilling, raise work or roof drilling can require a different tool class such as a stoper or a mechanized solution. Use only orientations permitted by the selected drill and leg documentation.

Application boundary: the purpose of the setup plan is not to prescribe a universal feed-force value. Feed control is model- and condition-specific. The buyer or site team should instead confirm that the leg can reach the intended collaring points, remain within its approved geometry and provide the required feed range without obstructing the working area.

4. Verify Air at the Working Face, Not Only at the Compressor

Pneumatic drilling performance depends on the air that reaches the drill under load. Compressor nameplate capacity is only the starting point. Long hoses, small internal diameter, restrictions, leakage, elevation and multiple tools operating at once can reduce delivered pressure and flow.

Current Atlas Copco underground-drill data illustrates why the air system cannot be ignored: several drills in the same 27–41 mm hole class are listed with substantially different air consumption at the same 6 bar reference condition. A model that fits the hole diameter may still be a poor system match if the face cannot supply its air demand.

PerfoMax’s current YT28 page, for example, lists reference air consumption of no more than 55 L/s at 0.50 MPa and no more than 81 L/s at 0.63 MPa for the referenced configuration. Those are model-screening values, not universal targets for every YT28-labelled machine. The final quoted supplier data sheet controls.

A practical air-system check

1. List every pneumatic tool expected to operate simultaneously at the face.
2. Use the selected manufacturer’s air-consumption figure at its stated test pressure.
3. Record air-hose inside diameter, total run length, couplings and known restrictions.
4. Measure dynamic pressure close to the drill while the system is operating.
5. If pressure falls materially under load, correct the air-delivery problem before interpreting slow drilling as a rock-drill problem.

5. Water Flushing Is Part of the Underground Drilling System

Water-flushed pneumatic drills are widely used in underground drilling because flushing removes cuttings from the hole and can support dust control. But water supply must be treated as a controlled service, not simply turned up until the hole looks cleaner.

The exact relationship between air and water pressure is manufacturer-specific. For example, PerfoMax’s current Y19A reference page states that, for that configuration, water pressure should remain at least 1 bar below air pressure to reduce the risk of water entering the impact mechanism. Do not transfer that number automatically to another drill: use the selected model’s manual and check pressure while the system is working.

When drilling performance deteriorates in a narrow heading, inspect the flushing path before increasing feed or changing the drill. Check the water source, hose, valve, drill-steel flushing passage and bit flushing holes. Restricted flushing can leave cuttings at the bit, increase regrinding and jamming risk, and make a healthy drill appear underpowered.

6. Drill-Steel Length Has to Fit the Heading and the Drill

A longer drill steel can reduce changes, but only if it can be handled, collared and supported inside the heading. In a tight working envelope, shorter steel may be more practical even when a longer steel is theoretically more productive. The correct choice therefore combines hole depth with working-space geometry.

PerfoMax’s current YT28 reference configuration uses an H22 × 108 shank and a 34–42 mm hole range. That does not mean every H22 rod or bit is automatically compatible. The H22 × 108 drill-steel page separately defines an 11° bit-connection option, while other tapered systems may use other angles. Confirm the rock-drill shank, steel length and bit taper independently.

7. An 8-Step Narrow-Tunnel Setup Workflow

1. Map the face. Record heading width, height, collaring points, hole angles and fixed services.
2. Define the hole. Confirm diameter, typical/max depth, pattern and rock condition.
3. Check the drill package geometry. Compare drill length, pusher-leg retracted/extended length, feed stroke and steel length with the available envelope.
4. Confirm the drill–leg pairing. Use the exact model/suffix and mounting interface; do not assume a family name proves fit.
5. Validate air delivery. Use rated consumption, hose dimensions, simultaneous loads and dynamic face pressure.
6. Validate water flushing. Confirm supply, pressure relationship, flushing passage and drainage using the selected manual.
7. Lock the drill steel and bit. Confirm shank, length, taper/thread, bit diameter and flushing layout.
8. Run a controlled site trial. Evaluate collaring, penetration, cuttings return, hose handling, repositioning time and wear before standardizing a fleet package.

8. Symptoms That Point to a Setup Problem

9. Common Mistakes in Narrow-Heading Air-Leg Drilling

• Selecting by drill model first: the heading geometry and air system may make the package impractical.
• Ignoring retracted leg length: a leg with adequate feed travel can still be too long to position in the opening.
• Using compressor rated output as face pressure: distribution losses can materially change the result.
• Increasing feed to compensate for poor flushing: the root cause may be cuttings removal rather than feed force.
• Ordering an FT160 leg without the suffix: family naming does not prove mounting or geometry compatibility.
• Specifying H22 without the bit-end connection: H22 × 108 and the taper angle describe different interfaces.
• Forcing one tool into every hole direction: some upward or special-position work requires another approved drill/support configuration.

10. What to Send in an RFQ for a Narrow-Tunnel Air-Leg Package

• mine/tunnel application and heading width × height;
• hole diameter, typical/max depth and drilling direction;
• rock type, fracture condition and water condition;
• current rock-drill model and manufacturer if replacing equipment;
• required pusher-leg model/suffix or current leg photos/marking;
• collaring height, available setup length and required feed travel;
• compressor model, available airflow, face pressure, hose ID and hose length;
• water supply and wet-drilling requirement;
• drill-steel shank, length, taper/thread and bit diameter;
• quantity, spare-parts requirement, destination and inspection documents.

For a current PerfoMax reference, review the YT28 air-leg rock drill and FT160-series pneumatic air legs. If the existing setup is already working, send photos of the drill nameplate, leg marking, drill-steel ends and hose connections through the PerfoMax RFQ page so the replacement package can be checked against the installed system.

FAQ

Are air-leg rock drills suitable for narrow tunnels?

Yes, they are commonly used in small underground drifts and tunnel headings where the opening and work method suit manual pneumatic drilling. The deciding issue is whether the complete drill, pusher leg, drill steel, hoses and operator working envelope fit the actual heading.

How do I choose pusher-leg length for a narrow heading?

Start with the available setup length and required collaring positions. Compare both retracted and extended length, feed stroke and the exact drill pairing. A double-telescopic leg can provide more reach from a shorter retracted package in some OEM systems, but compatibility must be confirmed model by model.

Why does an air-leg drill lose performance at the face?

A common system-level cause is insufficient delivered air under load. Long or undersized hoses, restrictions, leaks and simultaneous pneumatic loads can reduce pressure and flow. Measure close to the drill while operating before blaming the drill itself.

Should I use the longest drill steel that fits the hole depth?

Not automatically. Steel length also has to fit the heading, collaring geometry and handling method. A shorter steel can be more practical when a longer one cannot be positioned or supported safely.

Can I use the same air-leg drill for horizontal and upward drilling?

Only within the selected manufacturer’s approved configuration and orientation. Dedicated upward drilling can require a stoper or another support system. Do not improvise an unsupported orientation based only on the drill’s weight or power.

Technical Sources

• Atlas Copco — Pneumatic Underground Rock Drills and Pusher Legs
• Atlas Copco — BBD 94 W Underground Rock Drill
• Atlas Copco — ALF 67/80D Double-Telescopic Pusher Leg
• Atlas Copco — Power Technique Brochure 2026 Q1

Manufacturer examples are used to explain system logic, not as universal operating limits. Final air, water, feed, orientation and maintenance requirements must follow the selected equipment manual and the site’s approved procedures.