Short answer: in a typical hollow H22 tapered drilling assembly, air or water enters at the rock-drill end, passes through the drill steel’s central bore, crosses the rod-to-bit interface, exits through one or more flushing holes in the bit, and then carries broken rock back toward the collar through the annular space between the tool and the borehole wall. That description is a flow path, not a universal dimensional specification: “H22” identifies the hexagonal steel size family, but it does not by itself confirm bore diameter, shank length, taper angle, bit passage geometry, or the flushing arrangement of a particular machine.
This guide explains the components and terms a mine, quarry, contractor, or distributor should use when checking drawings or preparing an RFQ. It does not prescribe pressure, flow, or water volume. Those settings depend on the rock drill, hose system, rod and bit geometry, hole orientation, ground condition, and the equipment manufacturer’s operating instructions.
The H22 flushing path in one sentence
The useful mental model is a closed route with two different passages: the flushing medium moves forward inside the tool, while the mixture of flushing medium and cuttings moves back outside the tool. If either route is restricted, increasing supply pressure alone may not restore effective hole cleaning.
| Stage | Location | What happens | What must remain compatible |
|---|---|---|---|
| 1. Entry | Rock drill, water tube or air passage at the shank end | The machine introduces air or water into the drill-steel passage. | Machine flushing arrangement, shank geometry and seals or tubes specified by the drill manufacturer. |
| 2. Internal transfer | Central bore through the hollow hexagonal steel | The medium travels along the rod toward the tapered end. | Bore continuity, cleanliness and adequate cross-section for the approved setup. |
| 3. Interface transfer | Tapered rod end seated in the detachable bit | The medium crosses from the rod bore into the bit’s internal passage. | Correct taper family, full seating and aligned open passages. |
| 4. Bit discharge | Front or side flushing holes in the bit | The medium reaches the cutting face and the bottom of the hole. | Bit design, outlet condition and absence of packed debris. |
| 5. Return | Annular space around the rod and bit | The medium entrains cuttings and carries them toward the collar. | Enough clearance and an open return path for the actual cuttings and ground condition. |
What H22 tells you—and what it does not
In common drilling-tool terminology, H22 refers to a hollow hexagonal drill-steel family with a nominal 22 mm hex size. It is a useful starting point for identification, but it is not a complete interface standard on a purchase order. A buyer still needs to confirm the shank form and length, taper angle, rod length, bit socket, bit diameter, and flushing details.
The reason is simple: two parts can both be described as “H22” yet fail to form a complete working assembly. One may have a different shank length for the chuck, a different taper, or a different internal passage. The ISO 1718 standard page states that the standard covers basic drill-rod dimensions and the necessary dimensions of tapered connections. For procurement, that reinforces the need to verify the connection drawing rather than treating one size label as proof of every dimension.
If the uncertainty is at the machine end, use the checks in our H22 × 108 mm drill-steel compatibility guide. If it is at the detachable end, confirm the rod and bit as a matched set using the 7°, 11° and 12° taper compatibility guide.
Terms buyers and operators should use consistently
| Term | Practical meaning | Common misunderstanding |
|---|---|---|
| Central bore | The longitudinal passage through the hollow drill steel. | It is not automatically the same diameter in every H22 rod. |
| Flushing hole or outlet | A passage in the bit that releases air or water near the cutting face. | Bit-face appearance alone does not prove the internal passage matches the rod. |
| Annulus | The space between the outside of the tool and the borehole wall. | It is the return path, not the supply passage. |
| Cuttings return | The movement of broken rock from the hole bottom back to the collar. | Visible air or water at the collar does not always mean the bottom is being cleaned efficiently. |
| Shank-end flushing interface | The machine-side route that introduces the medium into the drill steel. | A correct taper at the bit end cannot compensate for a mismatched machine-side interface. |
| Passage continuity | An unobstructed route from machine entry to bit outlet. | Continuity is not the same as adequate capacity under load. |
How the flow path works step by step
1. The rock drill introduces the flushing medium
A pneumatic rock drill may use a dedicated water connection, an air-flushing arrangement, or another machine-specific system. The exact route through the drill’s front head, water tube, shank or chuck varies by model. Never infer it from the rod alone. Start with the rock-drill manual and the shank drawing, because a tube that does not reach or seal correctly can leak before the medium enters the rod bore.
2. The central bore carries the medium through the steel
The hollow core is part of the rod’s functional geometry. It must remain open from the shank end to the tapered end. Scale, corrosion products, compacted fines, manufacturing flash, or damage at an end can reduce the effective passage. A rod may therefore look straight and serviceable externally while its flushing performance is poor.
For an incoming inspection, do not assume that a nominal bore quoted by one supplier applies to all supply lots. Ask for the agreed drawing and the permitted inspection method. A go/no-go check, controlled air or water flow test, or visual borescope check may be appropriate, but the acceptance method should be agreed before shipment rather than improvised after a dispute.
3. The seated taper transfers flow into the bit
The taper’s main mechanical job is to locate the bit and transmit impact and torque through contact between matched surfaces. The flushing route must also remain open after the bit is fully seated. A correct external fit does not automatically prove that the internal passages are aligned or free from debris.
This is why buyers should request both the rod-end and bit-socket drawings when mixing sources. A nominally similar bit can seat too shallow, bottom incorrectly, or create a restriction at the passage transition. The safest procurement language is to name the taper angle and reference both mating drawings, then require an assembled flushing check on samples.
4. The bit outlets deliver flow to the cutting face
At the bit, the internal passage divides or turns toward face or side outlets. The exact number and orientation of holes depend on the bit design. Their job is to deliver the medium where fresh fragments are produced and to start moving those fragments away from the cutting face.
More outlets are not automatically better. Each design balances steel cross-section, carbide layout, face geometry and the available flushing supply. Buyers should compare complete bit drawings and application conditions, not rank bits by outlet count alone.
5. Cuttings return through the annular space
After leaving the bit, the medium must reverse direction and move back along the outside of the tool. The available return area changes with bit diameter, rod size, borehole condition and accumulated debris. Fractured ground, clay-rich seams, swelling material, an oversized rod for the hole, or a worn bit producing an irregular hole can all alter the return path.
This explains a common diagnostic trap: a clear rod bore and open bit holes are necessary, but they do not guarantee effective cleaning. The restriction may be outside the tool. Our separate guide on air versus water flushing in percussive drilling covers the different transport behavior and site considerations of the two media.
Air and water use the same route but behave differently
Both media can travel through the internal supply passage and return through the annulus, but they do not respond identically to leaks, fines, hole orientation or cold conditions. Air is compressible and can expand through restrictions; water is effectively incompressible in this context and makes leakage or blockage visible in different ways. Water can also support dust control, while site rules may limit dry drilling where respirable dust is a risk.
Do not convert a water-flushing setup to air, or the reverse, solely because the rod appears hollow. Confirm that the rock drill, connections, seals, hoses, bit and operating procedure are approved for the chosen medium. Local safety and environmental controls take precedence over production convenience.
Three checks that separate a terminology issue from a hardware problem
- Confirm the drawing stack. Put the rock-drill shank interface, rod bore and taper, and bit socket/outlet drawing on one page. Mark the intended flow route. Any undefined transition is an RFQ gap.
- Check components separately. Verify that the rod bore and bit holes are open before assembly. This distinguishes an internal blockage from a seating or machine-interface issue.
- Check the assembled route under the approved procedure. Use the manufacturer’s safe test method and compare a known-good assembly. A pass-through test confirms continuity; it does not by itself prove sufficient cleaning in rock.
Controlled weak-flow isolation matrix
Use one verified baseline assembly and change only one component at a time. Record the same observable for every stage—for example the approved flow indication, a timed collection under a water procedure, or the machine maker’s specified check. Do not compare an air result with a water result, or a bench check with an in-hole result.
| Comparison stage | Keep constant | Change or observe | What a meaningful difference indicates | Next decision |
|---|---|---|---|---|
| 1. Supply to drill | Approved hose, fittings, source and operating condition | Observe delivery at the defined drill-side test point | Low or unstable delivery exists before the drill steel | Correct the supply path; do not reject the rod |
| 2. Drill outlet or flushing entry | Same supply and approved machine setup | Check the outlet using the manufacturer’s safe procedure | Restriction or leakage follows the drill, water tube or entry interface | Hold the machine-side path for service |
| 3. Known-good rod versus suspect rod | Same drill, supply, bit or approved outlet fixture and procedure | Exchange only the H22 drill steel | The weak result follows one rod | Segregate that rod; inspect bore alignment, blockage and shank deformation |
| 4. Known-good bit versus suspect bit | Same drill, supply, rod, seating method and procedure | Exchange only the tapered bit | The weak result follows one bit | Inspect socket seating and flushing outlets; hold the bit, not the rod |
| 5. Open-path versus in-hole return | Verified drill–rod–bit assembly and approved parameters | Compare outlet continuity with cuttings return in the actual hole | The assembly passes outside the hole but return is poor in rock | Investigate annular clearance, packed cuttings, ground and hole condition |
Safety boundary: isolate and depressurize before separating any connection. Never look into an outlet, hold a loose component in a pressurized path, or improvise with high-pressure air, wire or a projectile-producing tool. Internal clearing and machine-side tests must follow the equipment maker’s procedure and site controls.
Release decision after the comparison
| Status | Evidence | Action |
|---|---|---|
| PATH VERIFIED | Identity is confirmed; passages are visibly open; the assembled result matches the verified baseline under the same procedure | Return the assembly to service and monitor cuttings return during the first controlled hole |
| HOLD FOR DRAWING | H22 identity is known, but bore, flushing entry, taper transition or bit-outlet compatibility is not controlled | Stop substitution and obtain the approved rod, bit and drill-interface specifications |
| SEGREGATE ROD OR BIT | The result follows one component during a matched comparison, or visible deformation and damage remain | Tag the component, prevent reuse and route it for the approved inspection or replacement decision |
| CHECK HOLE / RETURN PATH | The assembly passes the controlled check but in-hole return remains weak or intermittent | Do not condemn the rod; inspect annular clearance, packed cuttings, ground changes and operating setup |
Copy-ready flushing-path test record
Rock-drill model / revision: H22 shank length and marking: Rod supplier / item / length / lot: Taper angle and bit item: Flushing medium: Approved test procedure / observable: Supply-path result: Drill-outlet result: Known-good rod result: Suspect-rod result: Known-good bit result: Suspect-bit result: Open-path result: In-hole cuttings-return observation: Visible bore / shank / taper / outlet condition: Final status: PATH VERIFIED / HOLD FOR DRAWING / SEGREGATE / CHECK HOLE Inspector / date / photos or video reference:
Common mistakes when specifying H22 flushing
- Writing only “H22 rod.” This omits shank length, taper angle, rod length, bore requirement and the mating bit.
- Using outside diameter as a flow specification. The external hex does not define the central bore or bit outlets.
- Mixing a rod and bit because both are called tapered. Taper angle and mating geometry must match.
- Treating visible collar discharge as proof of good bottom cleaning. Flow may be bypassing, leaking or returning unevenly.
- Trying to cure every restriction with more pressure. A blocked passage, poor seating or inadequate annular return area requires diagnosis, not uncontrolled pressure escalation.
- Clearing a pressurized tool by hand. Trapped air, water and debris can release suddenly. Isolate, shut off and depressurize before disconnecting or probing any passage. The UK HSE’s compressed-air safety guidance describes hazards from pressure, hoses, particles and portable pneumatic equipment.
RFQ checklist for an H22 rod-and-bit flushing assembly
For a repeatable quotation, send one controlled specification rather than a collection of product names. Include:
- rock-drill make and exact model;
- shank size, form and length, supported by a drawing or verified sample;
- H22 rod length and taper angle;
- rod central-bore requirement and how it will be inspected;
- bit type, diameter, taper socket and flushing-hole arrangement;
- flushing medium: air, water or the machine-approved combination;
- hole orientation, expected depth range and ground description;
- drawing revision and acceptable dimensional tolerances;
- sample quantity for fit, continuity and controlled field testing;
- marking and packaging needed to prevent mixed tapers or supply lots.
If the supplier proposes a substitute, require a compatibility statement that addresses the whole route: machine entry, shank, rod bore, taper transition, bit outlets and annular return conditions. “Fits H22” is not enough.
Frequently asked questions
Is every H22 tapered drill rod hollow?
H22 tapered drill steels used with internal air or water flushing are commonly hollow, but the label alone should not be treated as proof of a particular bore. Confirm the drawing, product description and intended rock-drill system.
Does H22 define the flushing-hole diameter?
No. H22 identifies the external hex size family; it does not uniquely define the central bore or the bit outlet geometry. Those dimensions must be specified separately.
Can an air-flushing H22 rod be used for water flushing?
Possibly, but only if the rock drill, machine-side interface, rod, bit, hoses and operating procedure are approved for water. A hollow passage by itself does not establish system compatibility.
Why is flushing weak when the rod bore looks open?
The restriction may be at the rock-drill entry, the rod-to-bit transition, the bit outlets, a leak, or the annular return path outside the tool. Check the route in stages against a known-good assembly.
Should a blocked passage be cleared with pressure?
Do not apply uncontrolled pressure or probe a connected tool. Isolate the energy sources, depressurize the system, remove the component using the manufacturer’s procedure, and then inspect it with suitable tools and protection.
Specify the complete path, not just the rod name
A reliable H22 flushing assembly is a chain of compatible passages. The machine must introduce the medium correctly, the hollow drill steel must carry it without restriction, the seated taper must preserve the transition, the bit must discharge it at the face, and the borehole must provide a return route for cuttings. Treating any one of those stages in isolation creates avoidable fit and performance disputes.
Review PerfoMax’s drill rod range and the active H22 × 108 mm tapered drill rod inquiry page, or send the rock-drill model, shank drawing, taper angle, rod length, bit details and flushing medium through the request-a-quote form. Product pages do not replace the approved bore and interface drawings used for compatibility and release.