4.2.2. Rebound and Resistance

In the upward stroke, you supply air into the lower cylinder. When you supply air into this lowest cylinder, the hammer which was earlier in the lower cylinder will be pushed up into the upper cylinder. The air which was already there in the upper cylinder will expel out through the exhaust. So, basically what you are doing here is you supply air into the lower cylinder, which will push your hammer upward into the upper cylinder and expel the upper chamber's air.

During the upward stroke of a double-acting steam hammer, air is pumped into the lower cylinder. This causes the hammer to rise into the upper cylinder. As the hammer moves upward, the previously contained air in the upper cylinder is forced out through the exhaust. This action demonstrates how the pressure change can cause movement in the system, utilizing compressed air effectively.

Imagine you have a balloon filled with air. If you squeeze the balloon (analogous to supplying air), the air inside moves to another part and creates pressure. Similarly, the compressed air pushes the hammer upward.

In the downward stroke, air is supplied through the inlet into the upper cylinder. When you supply air into the upper cylinder, the hammer that was already there will be pushed into the lower cylinder. The air that was already in the lower cylinder will be expelled out through the exhaust.

For the downward stroke, air is introduced into the upper cylinder, pushing the hammer down into the lower cylinder. As the hammer descends, the air that was in the lower cylinder is expelled. This alternation of supplying air into different cylinders allows the hammer to rise and fall, effectively utilizing the principles of pneumatic energy.

Think of this process like a seesaw. When one side goes up, the other side comes down. Similarly, when air is pumped into one cylinder, the hammer rises, and when it's pumped into the other, it falls.

Most of the blow energy is derived from the steam energy. For both the upward stroke and the downward stroke, 90% of the blow energy is derived from the action of air or steam.

The operation of the double-acting hammer is heavily reliant on steam energy. This energy drives the hammer for both its upward and downward movements, meaning that strength doesn’t need to come predominantly from the hammer's weight. Instead, a lighter hammer can be used effectively because steam provides most of the necessary energy for movement.

Consider an air pump. It can inflate a large tire with relatively little effort due to the power of compressed air. In a similar way, the hammer utilizes steam pressure to achieve forceful impacts without being excessively heavy.

These double acting hammers are designed for lighter conditions; they are suitable for light to medium weight piles and for soil with normal frictional resistance. They should not be used for concrete piles due to the high blow rate.

The design of double-acting hammers is tailored for use in less challenging environments. They work well with lighter piles and soils that aren't overly resistant. Using them in heavy clay or with concrete piles, where the blow rate could cause damage, is inadvisable. Understanding the limitations of this equipment helps ensure safety and effectiveness.

Using the wrong tool for the job could lead to disaster - like trying to use a toy hammer to drive a steel spike. Similarily, using a double-acting hammer in tough conditions is impractical and likely to lead to failure.

The blow rate of these hammers is very high, ranging from 95 to 300 blows per minute, which can easily damage concrete piles.

The blow rate indicates how many times per minute the hammer strikes. While this high rate can be advantageous in some contexts, it can also pose a risk of damaging materials like concrete if not used correctly. Recognizing this helps operatives choose the appropriate equipment for the material they work with.

Imagine trying to pound a nail into a wall with a hammer that strikes too frequently. The nail might bend or break rather than going in properly. Similarly, excessive blow rates can cause damage to concrete piles.

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