The pile hammer is the impact mechanism (falling weight) of a pile driver that generates kinetic energy to drive piles, sheet piles, or structural members into the foundation soil. The weight of the hammer, drop height, and striking frequency determine the driving energy per blow — measured in kJ (kilojoules) or kNm.
Historically, pile hammers operated in free fall (free-fall hammer); today hydraulic pile hammers dominate: A hydraulic cylinder lifts the weight and additionally accelerates it downward during the fall (accelerated hammer). This generates more energy with the same hammer mass. Modern hydraulic pile hammers from Junttan, IHC, and Menck achieve driving energies of 30 to over 300 kJ per blow.
Diesel pile hammers use compression of a diesel-air mixture for acceleration — a combination of pile hammer and combustion engine. They are independent of external power supply, but are louder and more emission-intensive than hydraulic variants. In sensitive environments (city centers, nature reserves), vibration pile drivers are increasingly being used instead of impact hammers.