Down-the-Hole (DTH) hammers are widely used in mining, geothermal drilling, and construction due to their high drilling efficiency and reliability. However, even high-quality DTH hammers can experience performance issues such as no impact, weak impact, or intermittent impact during operation.
In this article, we’ll explain the main causes of DTH hammer failure and offer practical troubleshooting tips to help you minimize downtime and improve drilling efficiency.
Processing Defects in the DTH Hammer Components
The fit between the piston and the cylinder liner of a DTH hammer is extremely precise. This pairing requires high machining accuracy, excellent surface smoothness, and perfect cylindricity.
If the cylindricity is not maintained during manufacturing, the piston may stick intermittently or directionally. This causes the operator to frequently lift the drill rod for maintenance, significantly reducing productivity.
Another factor is the rigidity of the hammer casing. Poor rigidity can cause deformation when the hammer collides with the borehole wall during drilling. Repeated vibration, disassembly, and cleaning can further aggravate casing deformation, leading to internal part misalignment or jamming—eventually rendering the DTH hammer unusable.
Key tip: Always ensure high manufacturing precision and use a robust casing material to extend hammer lifespan.
Unreliable Backstop Seal at the Tail of the DTH Hammer
Most modern DTH hammers are equipped with a check valve (backstop valve) at the tail to prevent reverse flow. This valve typically relies on a spherical rubber cap or O-ring that seals via elastic deformation.
However, this design often causes the following problems:
Friction between the spring and guide device slows the valve’s cutoff speed.
Rubber seal wear due to repeated compression and friction reduces sealing effectiveness.
Spring fatigue may lead to backstop seal failure.
When air supply stops, the sudden drop in internal pressure may cause drilling mud or rock powder to flow back into the hammer cavity, jamming the piston.
In severe cases, water and cuttings enter the valve area, preventing normal air distribution and causing the hammer to expel debris without impacting.
Troubleshooting Tip: Regularly inspect the backstop valve assembly for spring fatigue and seal wear. Replace damaged components promptly.
Lack of Effective Sealing at the DTH Hammer Head
The drill bit of a DTH hammer usually has exhaust holes to communicate with the bottom of the borehole, and it connects to the hammer body via splines with a relatively large clearance.
When encountering groundwater or cementing fluid, liquid and solid mixtures may accumulate around the drill bit and the annular space. When the gas supply stops, the check valve closes quickly, trapping fluid inside the hammer cavity.
If excessive liquid enters the hammer, cuttings and debris may reach the piston area, increasing the likelihood of sticking. Over time, accumulated cuttings between the piston and drill bit reduce the efficiency of impact energy transfer, resulting in weak impact performance.
Maintenance Tip: Clean the hammer and bit regularly to remove cuttings and prevent liquid intrusion.
Drill Bit Stuck or Jammed
The spline fit between the DTH hammer and the drill bit is designed with some clearance, but when wet debris or mud accumulates, it can create a mud pack, causing the bit to stick.
If not addressed promptly, the mud pack enters the spline fitting gap, reducing the transfer efficiency of impact power. In severe cases, the drill bit and spline sleeve may lock together, halting drilling operations entirely.
Solution:
Keep the drilling area clean and dry as much as possible.
Use proper lubrication and flushing to prevent mud buildup.
Inspect the spline sleeve regularly for wear or contamination.
Final Thoughts
DTH hammer malfunctions often result from manufacturing inaccuracies, seal failures, fluid intrusion, or mechanical sticking. By understanding these causes and performing regular inspection, cleaning, and preventive maintenance, you can greatly extend the service life of your hammer and ensure consistent drilling performance.
