Extension Mechanism of Office Chairs

The extension mechanism of office chairs primarily relies on pneumatic rods or screw rod mechanisms to achieve height adjustment, with the core being the lifting action completed through the cooperation of mechanical structures with air pressure/threads.

Pneumatic Rod Mechanism: Rapid Adjustment Based on Gas Compression

The pneumatic rod is the most commonly used lifting device in modern office chairs. Its core principle is to achieve support and lifting by utilizing the change in the compression ratio of nitrogen gas inside a sealed cylinder. The cylinder is internally filled with high-pressure nitrogen gas and is divided into upper and lower chambers by a piston. When a user sits down, their body weight presses on the piston, compressing the gas in the lower chamber and increasing the air pressure to balance the gravity. When height adjustment is needed, operating the control lever beneath the seat triggers an internal valve:

• Lowering Process: The valve opens, connecting the upper and lower chambers. The high-pressure gas in the lower chamber is released to the outside or into the upper chamber, causing the piston to move downward due to the air pressure difference, and the seat lowers accordingly.
• Raising Process: Gas is supplemented into the upper chamber through an external air pressure pump (some designs are integrated into the control lever), increasing the air pressure in the upper chamber, pushing the piston upward, and raising the seat.

The adjustment speed of the pneumatic rod is relatively fast, allowing users to complete the operation without leaving their seats. Additionally, nitrogen gas has stable chemical properties, ensuring high safety. However, it should be noted that poor-quality pneumatic rods may pose risks of gas leakage or explosion due to insufficient sealing, so it is essential to choose products that have passed safety certifications.

Screw Rod Mechanism: Mechanical Adjustment Through Thread Cooperation

The screw rod mechanism is a traditional lifting method for office chairs, with a principle similar to the rotational lifting of threaded screws. A vertical screw rod is installed at the bottom of the seat, with threads on its body that mesh with a fixed nut or gear structure on the base. During adjustment:

• The user rotates the seat or a dedicated adjustment knob to drive the rotation of the screw rod.
• Since the nut or gear remains stationary, the screw rod is forced to move axially (upward or downward), thereby changing the height of the seat.
• After adjustment, the frictional force between the threads or a locking device (such as a catch) fixes the position of the screw rod, preventing accidental movement of the seat.

The screw rod has the advantages of a simple structure, low cost, and no reliance on gas. However, manual rotation is required for adjustment, resulting in a relatively slow speed. Additionally, long-term use may lead to thread wear, causing adjustment difficulties.

Both mechanisms are designed with ergonomics in mind, allowing users to quickly adjust the seat height according to their height or work requirements to maintain a correct sitting posture (such as keeping both feet flat on the ground and knees at the same height as the hips), reducing fatigue from prolonged sitting, and serving as a basic functional configuration in modern office environments.