It will explain the classification standards for high and low air pressure, detail the 90A hammer's working mechanism, technical advantages, and typical applications, and compare it with high-pressure technology, discussing its enduring value as a classic in modern drilling operations.

​​1. Introduction: The "Heart" of Rock Drilling and the Choice of Air Pressure​​

DTH hammer drilling is a highly efficient method in modern geotechnical engineering, with the hammer serving as the "heart" of the system. It utilizes the energy of compressed air to generate high-frequency, high-energy impacts directly on the drill bit to break the rock. 

The starting point for understanding the 90A is its clear identity as a ​​low-air-pressure​​ tool. Understanding the 90A first requires understanding what constitutes ​​low air pressure​​ and the engineering logic behind this choice.

​​2. Defining High and Low Air Pressure: The 90A's Technical Coordinates​​

To position the 90A, a clear frame of reference is needed. The industry typically classifies hammers based on the pressure of the compressed air that drives them:

• ​​Low-Air-Pressure Hammers​​: Typically operate in the range of ​​0.7 MPa to 1.05 MPa​​ (approximately 100 to 150 psi). This is the longest-established and most widely used technology platform.
• ​​Medium- to High-Pressure Hammers​​: Operate at higher pressures, typically ​​1.4 MPa to 2.0 MPa​​ (approx. 200 to 290 psi), offering significantly higher impact energy and penetration rates.
• ​​High-Pressure Hammers​​: Operate at ​​2.4 MPa to 3.0 MPa​​ (approx. 350 to 435 psi) or higher, representing cutting-edge technology designed for large-scale mines where maximum penetration rates are critical.

The recommended operating pressure for the Atlas Copco ​​COP 90A​​ hammer is typically ​​0.5 MPa to 0.7 MPa​​ (approx. 70-100 psi). This data clearly anchors it in the ​​low-air-pressure​​ category. This fundamental design choice means the 90A was intended to be paired with the most common and widely available standard screw compressors, a positioning that fundamentally shaped its technical characteristics, advantages, and market destiny.

​​3. Working Principle and Technical Advantages of the 90A Hammer​​

As a classic, valved ​​low-pressure hammer​​, the 90A features a refined and efficient design. Its operating cycle can be simplified into four stages:

1. ​​Return Stroke:​​ Compressed air travels down the drill string into the hammer, pushing the piston upward (return stroke) and storing kinetic energy.
2. ​​Valve Shift:​​ As the piston reaches a specific point, the air distribution valve shifts, reversing the flow of air.
3. ​​Power Stroke:​​ High-pressure air is now directed in front of the piston, driving it at high speed downward (power stroke) to convert its stored kinetic energy into impact energy.
4. ​​Energy Transfer:​​ The piston strikes the tail of the drill bit, transferring energy through the bit to crush the rock at the bottom of the hole. After impact, the valve shifts again, restarting the return stroke and beginning a new cycle.

This proven principle, implemented on a ​​low-pressure​​ platform, gives the 90A several core advantages:

• ​​Exceptional Reliability:​​ ​​Low air pressure​​ means the mechanical and thermal stresses on internal components (like the piston and valve) are relatively lower. This allows for a more robust construction, resulting in longer part life and significantly reduced failure rates. In harsh mining environments, reliability is often a more critical metric than peak performance.
• ​​Excellent Economy:​​ This is the most significant competitive edge of a ​​low-pressure hammer​​. Firstly, the compressors required to power the 90A are smaller, consume less fuel, and have lower operating costs. Secondly, the initial investment for the equipment is lower, and its simple design means maintenance is less technically demanding and spare parts are relatively inexpensive.
• ​​Broad Equipment Compatibility:​​ The 90A can be easily matched with various small-to-medium-sized, highly mobile drill rigs (like crawler drills). This makes it ideal for confined quarries, complex terrain on hydroelectric sites, and other locations where larger, high-pressure rigs cannot easily operate.
• ​​Strong Adaptability:​​ For medium-hard and softer rock formations, the 90A's performance is more than sufficient. Its ​​low-pressure​​ characteristic also results in a relatively gentler airflow for exhaust and cuttings removal, which can help maintain hole stability in certain fractured ground conditions.

​​4. Classic Application Scenarios: Where Does the 90A Excel?​​

Thanks to these advantages, the ​​90A hammer​​ is an indispensable tool in the following areas:

• ​​Secondary Breaking in Mines:​​ In large open-pit mines, oversized rocks need to be broken down. The 90A, paired with a drill rig for smaller blast holes, is the standard solution due to its high mobility and low operating cost.
• ​​Quarries and Aggregate Plants:​​ This is the traditional domain of the 90A. Quarry rock types vary but are often medium-hard, with typical hole diameters between 90mm and 115mm, perfectly matching the 90A's performance range.
• ​​Water Conservancy, Hydroelectric, and Infrastructure Projects:​​ For drilling anchor bolts, foundation support, and exploration holes, rigs equipped with the 90A can adapt to rough terrain and perform various tasks.
• ​​Construction:​​ Used for foundation work, rock bolting, and other drilling applications.

In these scenarios, the goal is often not ultimate single-hole speed, but the optimal balance of overall cost, efficiency, and reliability. The 90A is a masterclass in achieving this balance.

​​5. Comparison with High-Pressure Technology: Not Replacement, but Complement​​

Comparing the ​​90A low-pressure hammer​​ with modern ​​high-pressure hammers​​ (like Atlas Copco's COP 66/94 series) clarifies its positioning.

Thus, ​​high-pressure technology​​ is designed for ultra-large mines where economies of scale are paramount, aiming to maximize meters drilled per rig to offset the high capital investment. The ​​90A​​, representing ​​low-pressure technology​​, serves small to medium projects that are more sensitive to overall costs and have diverse operational needs. The relationship is not one of "advanced" replacing "obsolete," but rather ​​complementary​​ technological paths developed for different market demands.

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