Single Acting Hammer:

• In single acting pile driving the ram of hammer is raised by the steam or compressed air when works on the underside of the piston.
• When the ram reaches the top of upward stroke, the pressure of the steam or air is released, which results in the fall of the hammer by gravity.
• The weight of ram of these hammers are generally available in the range of 1.5 to 10 tonnes, thus making overall weight of hammer between 2 to 20 tonnes.
• The number of blows per minute are generally around 60.
• These hammers can also be used under water, where the hammers are lifted and dropped in an enclosed casing.
• As they deliver heavy blows at faster speed, the time required for driving operation is lesser as compared to the drop hammers.
• The speed of driving is slower than that of double acting hammer hence it is less suitable where very fast driving of lighter piles is required.
• These hammers cost less than double acting hammer but need more investments.

Double acting hammer:

• This is similar to single acting hammer except that steam or air acts on both sides of piston in this type of hammer.

• Steam or air raises the ram to the top of the driving stroke and then drives it down in its downward stroke.

• This also increases the speed of downward motion and thereby increases the number of blows per minute.

• In this case steam or air is admitted above the piston, after piston reaches to the top during its upward stroke.

• During the same time the fluid is allowed to escape from the underside of the piston.

• The speed of the ram is about 100 blows per minute.

• The energy delivered by each blow is about 20% more due to steam pressure assisted gravitational force during downward stroke.

• These hammers are capable of fast driving of light or medium heavy piles in hard soils.

• These are also suitable to drive steel sheet piles.

Below is the diagram for both Single & Double acting hammer:-