Why Your DTH Hammer Stopped Hitting: Five Failures and How to Tell Which One You Have

A DTH hammer that won't hammer isn't subtle about it. The penetration stops. The sound changes — from a sharp rhythmic crack to a dull thud or nothing at all. The return air feels wrong. Something's broken, or jammed, or worn past the point of function.

The question is what. Tearing down a hammer at the bottom of a hole is not where you want to be doing detective work. Here are the five most common reasons a DTH hammer quits, what each one looks and sounds like from the surface, and what you'll find when you open it up.

Failure 1: The Hammer Ran Dry

What you'll notice: the hammer was working fine, then gradually the impact sound softened. Penetration slowed. The return air felt hotter than normal. By the time it stopped hammering entirely, the damage was already done.

What happened: the lubricator ran empty, the oil line clogged, or someone forgot to refill it between holes. The piston ran against the cylinder wall with no oil film. Metal-on-metal at fifty blows per second generates heat and wear particles. Within minutes, the clearance between piston and cylinder grows past the point where the air can build pressure behind the piston — the air leaks past instead of driving the stroke.

The fix: open the hammer. If the piston and cylinder are scored, they're done — replace both. If the scoring is light, polish it out with fine emery and reassemble with proper lubrication. Then fix the lubrication system that caused the problem in the first place. Check the in-line lubricator. Verify oil is reaching the hammer by feeling the exhaust — it should be slightly oily, not dry. Top up before every hole.

Failure 2: Something Is Blocking the Air

What you'll notice: the hammer stopped suddenly, not gradually. No impact sound at all. Return air is weak or absent. The compressor is running normally — pressure at the regulator is fine — but nothing's getting to the bottom.

What happened: debris blocked the air passage. Could be a piece of rust scale from inside a drill pipe that wasn't blown out before connection. Could be a foreign object that fell into the backhead while the hammer was sitting on the rack. Could be cuttings that backflowed into the hammer when the air was cut without lifting off bottom.

The fix: pull the string. Check the air passage through each component — backhead, check valve, distributor, piston bore. Clean everything. Before reassembly, blow out every drill pipe. Cap the hammer backhead when it's not connected. And never kill the air with the hammer on bottom — lift off first, blow the hole clean, then shut down.

What you might also find: excessive clearance between piston and cylinder, or between piston and distributor. These gaps bleed air pressure and reduce impact energy even if they don't stop the hammer completely. If the hammer was hitting weakly before it stopped, measure the running clearances. Anything beyond the manufacturer's wear limit means replacement.

Failure 3: Water and Mud Got Inside

This is the sneaky one, because the problem started when the hammer wasn't even running.

The mechanism: a DTH hammer has two paths for liquid to enter when the air is off. One is the bit exhaust hole — it's open to the bottom of the hole. The other is the spline clearance between the bit shank and the chuck — it's a loose sliding fit with plenty of gap.

When you stop the air to add a pipe or pump grout, the check valve at the top of the hammer closes. The hammer becomes a sealed cavity — or mostly sealed. If the hole has standing water, that water sees two entry points: the open exhaust hole and the spline gap. The water level outside the hammer is higher than the air pocket inside, so water pushes in — like submerging an upside-down cup.

The water carries cuttings with it. Fine abrasive particles settle into the piston-cylinder clearance, into the distributor, onto the check valve seat. When the air comes back on, those particles are trapped in running clearances measured in thousandths of an inch.

What you'll notice: the hammer runs intermittently. Hits a few times, stops, hits again. Or it runs weakly — impact energy is low because the piston is dragging through grit. The sound is irregular and muffled.

The fix: disassemble and thoroughly clean every internal part. If the piston or cylinder shows scoring from the grit, replace. Prevention: when drilling in wet conditions, keep the hammer running whenever it's in the hole. If you must stop the air, lift the hammer well above the water level if possible. And never leave a non-running hammer sitting at the bottom of a wet hole.

Failure 4: The Bit Is Stuck in the Chuck

What you'll notice: the hammer is running — you can hear the impact — but penetration has stopped. The bit isn't advancing. Rotation torque might be fluctuating.

What happened: wet, sticky cuttings formed a mud cake around the bit shank and the chuck. The mud worked its way into the spline clearance. The bit, which needs to slide freely in the chuck to transmit impact to the rock, is now bound by compacted debris. The piston is hitting the bit shank, but the bit can't move forward because it's jammed in the chuck.

This is common in wet drilling through clay or shale formations. The cuttings don't blow dry — they form a paste that packs into every available gap.

The fix: pull the hammer. Clean the bit shank and chuck splines thoroughly. Check that the bit slides freely in the chuck with no binding and no excessive play. If the splines are worn or galled, replace the affected parts. In the future, increase air volume to improve hole cleaning in wet formations, and consider reducing water injection if the cuttings are coming out as mud.

Failure 5: Your "Drilling Fluid" Is Full of Grit

What you'll notice: the hammer was working fine, then started running erratically. The impact rhythm is uneven. Maybe the check valve is sticking.

What happened: someone decided to save money on foam by pumping a laundry detergent solution down the hole instead of proper drilling foam. Laundry detergent doesn't fully dissolve — there are always particles, binding agents, anti-caking compounds. Those particles travel with the fluid straight into the hammer's internal air circuit. They gum up the distributor valve. They pack into the piston clearance. They stick the check valve open or closed.

The hammer was designed for clean air with a small amount of properly formulated rock drill oil. It was not designed for a slurry of undissolved household chemicals.

The fix: strip the hammer completely. Clean every part with solvent. Reassemble with proper lubrication. And stop putting laundry detergent in the hole. Use purpose-formulated drilling foam that dissolves completely and leaves no residue. The cost of proper foam is a rounding error compared to the cost of a hammer rebuild — or a lost hole because the hammer quit at depth.

The Diagnostic Pattern

When a DTH hammer stops, work through the possibilities in this order: lubrication (gradual decline = dry running), air supply (sudden stop = blockage), contamination (erratic running = water, mud, or grit inside), mechanical binding (running but no advance = stuck bit), and fluid quality (unpredictable behavior = something in the air that shouldn't be there).

The hammer tells you what's wrong. You just have to listen before you pull it, and look carefully when you open it.