Summary
Choosing a DTH Hammer comes down to one design decision that most quotations never explain: does the bit carry a foot valve or not? The difference is not cosmetic. A foot-valve hammer uses a blow tube inside the bit to time air distribution, running a heavier, longer-stroke piston that delivers fewer but harder blows — the right profile for very hard rock. A valveless hammer replaces that tube with a guide sleeve on the piston's lower end, using a lighter, shorter-stroke piston that strikes faster, drills 15% to 30% quicker in soft and medium formations and consumes over 10% less air. Series names differ too: DHD, QL, SD and COP for foot-valve duty, Mission, DHD-W, QL-W and AME-W for valveless. This release sets out both architectures, the series that use them, and a practical method for matching the choice to your rock, your compressor and your cost per metre. Getting it wrong is expensive in ways that never appear on the invoice; getting it right is a specification decision, not a price decision.
What: Two DTH Hammer Designs Explained
All down-the-hole tools share one working principle. Compressed air is fed down the drill string into the hammer, where an air distributor, internal cylinder, piston and piston case form a precise air distribution system. The piston reciprocates inside that system, converting air energy into mechanical impact energy, which is transmitted through the bit shank into the bit and then into the rock. The exhaust air leaves through the bit face and lifts cuttings up the annulus. What changes between designs is how the air timing is controlled, and that single detail changes the piston's mass, stroke and blow rate.
Design one: hammers for bits with a foot valve. The foot valve is also called a blow tube, plastic tube or check tube, depending on the supplier — all four names describe the same component. It sits inside the bit and works with the piston on a sealing principle, acting as the valve that times air distribution inside the hammer. Hammers built this way use a heavier, shorter piston with more volume in the air distribution system. The result is a lower impact frequency with greater force per blow at the same air pressure. Series in this family include DHD3.5, DHD340, DHD350, DHD360, DHD380, QL40, QL50, QL60, QL80, SD4, SD5, SD6, SD8, and COP34, COP44, COP54, COP64 and COP84.
Design two: hammers for bits without a foot valve. Often called valveless or tubeless hammers, these tools use the smaller lower end of the piston against a guide sleeve to take over the foot valve's role. The piston is longer, the air distribution system is more compact and the stroke is shorter, producing a faster impact frequency with less force per blow. Series in this family include Mission 30, 40, 50, 60 and 80; the DHD-W improvements such as DHD2.5W, DHD3.5W, DHD340W, DHD350W, DHD360W and DHD380W; the QL-W improvements QL50W, QL60W and QL80W; and the AME-W range covering W46, W56, W66, W86, W106, NM126W, W156 and W186.
Why: What the Choice Costs You
The commercial consequences of getting this wrong are larger than most buyers expect. A hammer and bit combination that is technically sound but mismatched to the formation will still drill a hole — it will simply cost more per metre, consume more fuel and require more bit resharpening than it should. Four differences drive that cost.
Formation match decides penetration rate. A foot-valve DTH Hammer concentrates energy into fewer, harder blows. In very hard, brittle rock that is exactly what breaks the face efficiently: the bit penetrates on impact and the chips release cleanly. Put that same hammer in soft or medium-soft ground and the energy is wasted — the rock deforms rather than fractures, penetration slows and the bit polishes instead of cutting.
Impact frequency decides productivity in softer ground. The valveless architecture strikes faster with lighter blows. Field comparisons put drilling speed 15% to 30% higher than foot-valve equivalents in soft and medium formations, which on a production site converts directly into metres per shift and lower cost per metre.
Air and fuel consumption decide the running cost. Valveless hammers consume over 10% less air than foot-valve hammers, and every litre per minute saved at the hammer is compressor power and diesel that does not have to be paid for. On multi-rig sites running two shifts, that line item is not marginal.
Failure modes decide downtime. The foot valve is a wear item exposed to thermal expansion and contraction, and a broken or damaged tube stops the hammer. The valveless design removes that component entirely: fewer parts, simpler internal structure, lower overall failure rate, less frequent dismantling and less unplanned downtime. For contract drillers paid by the metre, a hammer that does not stop is worth more than one that is marginally faster in the wrong rock. Working through these four points in order — formation, frequency, air, failure mode — is how a fleet should select a DTH Hammer rather than inheriting whatever was in the last quotation.
And it decides what you carry in the workshop. Two architectures mean two spare-parts lists. A fleet that standardises on one family gains simpler inventory, faster rebuilds and clearer operator training; a fleet that mixes families without a rule ends up stocking both foot valves and guide sleeves, and rebuilding hammers that never suited the holes they were assigned to. Matching design to formation is therefore an inventory decision as much as a technical one, and it pays back every season rather than only on the first contract.
How: Matching Design to Rock and Rig
The selection logic becomes concrete when it is applied to real duty. Below are three typical configurations and the reasoning behind each.
Hard rock benching in granite or hard limestone. A 4-inch to 6-inch hole in very hard, abrasive rock is foot-valve territory. A DHD350, DHD360 or QL60-class hammer with a foot valve delivers the heavier blow the face needs, and the longer service life of the case matters because abrasive rock wears the barrel quickly. Buttons are usually spherical for hard brittle formations, with rotation speed set so the buttons index across the face instead of tracking one groove. Watch cuttings return at the collar: rising back pressure signals the hammer is losing impact energy before the pressure gauge shows it.
Soft to medium formations and high-production water well work. Here the valveless family earns its place. A DHD360W or QL60W-class hammer runs the faster, lighter blow pattern that keeps penetration high in shale, sandstone, soft limestone and weathered zones, with 15% to 30% faster drilling and over 10% lower air demand. Because there is no foot valve to break, the hammer tolerates the thermal cycling that comes with long, hot shifts. Contract drillers running continuous water well programmes often standardise on the W series for exactly this reason.
Mixed ground and casing programmes. Where a hole starts in overburden and finishes in hard rock, the DTH Hammer has to survive both regimes. A foot-valve unit gives the hard-rock performance at depth; a valveless unit gives the speed and air economy through the softer upper section. Where casing is required, a guided chuck casing arrangement keeps the string on axis so the hole enters bedrock at the designed position rather than wandering.
| Selection point | Foot valve (blow tube) design | Valveless (tubeless) design |
|---|---|---|
| Air timing component | Foot valve or blow tube inside the bit | Guide sleeve acting on piston lower end |
| Piston profile | Heavier, shorter piston, larger air chamber | Longer piston, compact air system, short stroke |
| Blow character | Lower frequency, greater force per blow | Higher frequency, lighter force per blow |
| Best formation | Very hard, brittle rock | Soft to medium-soft rock |
| Drilling speed | Baseline | 15% to 30% faster in suitable ground |
| Air consumption | Baseline | Over 10% lower |
| Typical failure point | Foot valve breakage, thermal damage | Fewer parts, lower failure rate |
| Representative series | DHD, QL, SD, COP | Mission, DHD-W, QL-W, AME-W |
One more field rule is worth writing into the tender. Test any hammer on the formation you actually drill, not on the supplier's demonstration block. A short trial hole, measured in metres per hour and air pressure at the collar, settles in an afternoon what a specification sheet argues about for weeks, and it gives your operators the feel of the blow pattern before the fleet standardises on it.
What to check before ordering. Confirm the rock type and uniaxial strength, the hole diameter and depth, the compressor's free air delivery at working pressure, and the bit shank interface. Then confirm which family the quoted hammer belongs to, and ask what the alternative would deliver. A supplier who can explain the trade-off in blows per minute and air volume is a supplier who understands the tool; a supplier who quotes only on price is transferring the risk to your cost per metre. Ask for blow rate, working pressure window and recommended lubrication rate in writing: those three numbers, not the headline price, show whether the tool actually fits the compressor you own. Every DTH Hammer we ship is matched this way — formation first, then air package, then bit, then thread.
FAQ
These are the six questions buyers raise most often when comparing the two architectures.
What is a foot valve in a DTH hammer?
A foot valve is the tube inside the bit, also called a blow tube, plastic tube or check tube. It works with the piston on a sealing principle to time air distribution inside the hammer. Hammers built around it use heavier, shorter pistons for fewer but stronger blows, which suits very hard rock formations.
Which rock should use a valveless hammer?
Valveless or tubeless hammers suit soft to medium-soft formations such as shale, sandstone, soft limestone and weathered zones. Their longer piston and shorter stroke produce faster, lighter blows, giving 15% to 30% higher drilling speed in suitable ground plus over 10% lower air consumption compared with foot-valve equivalents, which is why they dominate soft-ground water well programmes.
Do valveless hammers really save air and fuel?
Yes. Measured against foot-valve hammers, air consumption is more than 10% lower. Because compressor output is the dominant energy cost on a drilling site, that reduction converts into fuel savings and, on multi-rig programmes running two shifts, a clearly measurable drop in cost per metre drilled over a full season.
What are the main failure risks of each design?
The foot valve is a wear item exposed to thermal expansion and contraction; breakage or damage stops the hammer and requires dismantling. The valveless design removes that component, leaving a simpler internal structure, a lower overall failure rate and less frequent teardown, which cuts unplanned downtime on site and shortens the rebuild queue at the workshop.
Can one hammer cover both soft and hard ground?
Not ideally. The piston mass, stroke and air timing are optimised for one regime. A foot-valve hammer wastes energy in soft ground, while a valveless hammer loses efficiency in very hard brittle rock. Fleets drilling mixed ground normally keep both families, or plan the hole sequence so each section uses the matching tool.
How do I confirm which series fits my rig?
Match the bit shank, hole diameter and compressor free air delivery at working pressure, then select the series. DHD, QL, SD and COP cover foot-valve duty; Mission, DHD-W, QL-W and AME-W cover valveless duty. Send your rock type, hole size and compressor data and we return a matched recommendation with the blow rate and pressure window stated.
Conclusion
There is no universally better DTH Hammer design; there is only the right match between air timing, piston behaviour and the rock in front of the bit. Foot-valve hammers concentrate force for very hard formations, valveless hammers trade force for frequency, speed and air economy in softer ground, and the cost per metre follows that choice. Getting it right is a five-minute conversation about formation, hole size and compressor output, and it is usually worth several percentage points of margin on a drilling contract. Match the tool to the ground, and the ground stops being the variable you cannot control.
Send us your rock type, hole diameter, depth and compressor specification, and we will return a matched hammer and bit recommendation with the reasoning behind it. You can also request our full catalogue, ask for a comparison of the two designs against your own drilling data, or discuss a custom configuration for mixed-ground programmes. Contact our drilling team today to get your quotation started.
