On Lin Mo's workbench lie three permanent items: a vernier caliper, a bottle of adhesive, and a row of sleek silver 16g CO2 cartridges.
No longer than a finger, these metal canisters have cold, frosty shells. For cycling enthusiasts, they are a lifesaver when tires burst. For Lin Mo, they are weights that hold the world's fragile balance in check.
A top-tier pneumatic precision instrument restorer, Lin Mo possesses an almost obsessive sensitivity to air pressure. He does not mend ordinary toys, but high-precision devices disabled by unstable air pressure-ranging from decades-old pneumatic nail guns to modern portable medical breathing aids.
"Master Lin, can this still be fixed?"
The speaker was a sweating young man clutching a worn metal box. Inside was a vintage pneumatic shutter controller, once used to capture high-speed motion.
"The internal spring is broken, and the air valve is leaking," the young man urged anxiously. "This was my grandfather's. It originally paired with old threaded CO2 cartridges, which are impossible to find now. I tried retrofitting modern 16g cartridges, but the pressure is too strong. The moment I screwed one on, the sealing ring blew apart with a bang."
Lin Mo said nothing and picked up the heavy metal box, which reeked of aged oxidation. He slipped on a monocle and narrowed his eyes to examine the valve connector.
"It is not excessive pressure that caused the failure," Lin Mo murmured softly, as if fearing to disturb the dust on his desk. "It is your impatience."
He pulled a brand-new 16g cartridge from his drawer. Its surface glinted silver, sealed with a tiny copper bead at the nozzle.
"Sixteen grams of liquefied carbon dioxide, sealed under pressure. Once released, it expands over six hundred times in volume." Lin Mo stroked the cartridge gently with his fingertip. "It is docile if you do not force it. But compress it recklessly, and it becomes a miniature bomb."
The young man swallowed hard. "So… can you repair it?"
"I can. But I have one rule." Lin Mo looked up, his gaze sharp behind the lens. "You must perform the first pressure test after the repair. And no brute force."
After a moment of hesitation, the young man nodded.
For the next three hours, the workshop echoed only with faint metal friction. Lin Mo disassembled the valve, reground the sealing surface, and reshaped the gaskets with custom rubber. His movements were deliberate and unhurried, like a surgeon performing delicate surgery.
The final step was adapting the device to fit the 16g CO2 cartridge.
Lin Mo crafted a custom adapter. Instead of a rigid threaded lock, he designed a spring-buffered thimble structure to ease pressure surges.
"Listen carefully," Lin Mo said, handing the modified controller to the young man. "The greatest danger with CO2 cartridges is overpressurization-sudden, forceful gas release. As you twist the cartridge, feel the resistance. That is the gas meeting yours. Yield slightly, give it room, and it will flow steadily."
Still confused, the young man took the controller and began screwing on the 16g cartridge.
"Slow down," Lin Mo warned.
The young man took a deep breath and twisted gently.
Hiss--
A faint stream of air escaped, followed by crisp mechanical clicking. The pressure gauge needle settled steadily in the green safe zone. No explosion, no leakage.
"It works!" the young man exclaimed in delight. He squeezed the shutter, which clicked sharply and reliably.
Leaning back in his chair, Lin Mo let out a long breath. He stared at the empty, weightless spent cartridge, stripped of its original heft.
"Do you know why these small cartridges are so dangerous?" Lin Mo asked suddenly.
Still buzzing with excitement, the young man blinked in surprise. "Is it the high internal pressure?"
"No." Lin Mo shook his head and twirled the empty canister under the lamp. "It is because they are small. People assume something this tiny cannot harm them, so they ignore the risks. It is just like the trivial pressures in life. Disregard them, let them build to a breaking point, and the energy unleashed in an instant will destroy everything."
The young man's smile faded as he gripped the controller. He thought of skipping three hours of sleep nightly for weeks to rush deadlines, of his short temper with his family, and the endless anxiety he had forced himself to suppress.
"This device will serve you well for years," Lin Mo said, beginning to tidy his tools. "But remember this next time you replace the cartridge: never force it. Sometimes, stepping back is the tightest seal."
The young man paid his fee and left, overflowing with gratitude.
Watching his figure vanish around the corner, Lin Mo returned to his workbench. He picked up another unopened 16g cartridge, the cold chill of its metal surface seeping into his fingertips.
In this high-stakes city, every person is a sealed 16g CO2 cartridge. Tough and cold on the outside, yet harboring immense compressed energy within. Only by learning to control the pace of release can one avoid shattering themselves in an unguarded moment.
Outside the window, the setting sun gilded the city skyline. Lin Mo placed the cartridge back on the shelf, where dozens of identical silver cylinders stood in neat rows-a silent army, waiting to be awakened with gentle care.
