Office Chair Sinking Phenomenon

The sinking of an office chair when sitting down is usually a normal mechanical and structural reaction, but abnormal sinking may indicate component damage and requires judgment based on the specific situation.

1. Instantaneous Effect of Action and Reaction Forces
   According to Newton's third law, when a person sits down, they exert a downward force on the chair, and the chair's support structure simultaneously generates an upward reaction force. During this process, the seat may experience a slight sinking (usually less than 1 centimeter) due to material elasticity or structural gaps, which is a transient phenomenon before mechanical equilibrium is established and is not a cause for concern.

2. Elastic Deformation and Energy Absorption by Cushioning Materials
   If the chair's seat uses elastic materials such as foam, springs, or gas cylinders, it will deform under pressure to distribute the load. For example, the gas cylinder in a pneumatic height-adjustable chair is filled with high-pressure nitrogen gas. When sitting down, the piston compresses the gas, reducing its volume and causing the seat to slowly descend by 1-2 centimeters. This deformation is a manifestation of the chair's cushioning function. If the seat fully rebounds and makes no abnormal noises after standing up, it falls within the normal design range.

3. Working Characteristics of Gas Cylinders and Abnormality Detection
   The gas cylinder is the core component of a pneumatic height-adjustable chair, and its sealed design allows for a small amount of movement to enable height adjustment. A brief sinking of the seat when sitting down is a normal reaction to gas compression. However, the following situations require caution:

• Inability to rebound: If the gas cylinder's seal fails, causing gas leakage, the seat will continue to descend to the lowest point.
• Abnormal noises: Worn internal parts or gas leakage may be accompanied by metal friction sounds or gas escape sounds.
• Sudden drop: If the internal pressure of the gas cylinder becomes unbalanced or the structure breaks, the seat will descend rapidly.
  In such cases, use should be stopped immediately, and the gas cylinder should be replaced.

4. Impact of Structural Differences on the Sinking Experience
   The sinking amplitude and feel vary significantly among different types of chairs: Hardwood chairs have high material rigidity, making deformation almost imperceptible; soft-cushioned sofas or pneumatic swivel chairs have a more pronounced sinking feel due to their soft seats and multiple elastic components. After long-term use, the foam may collapse due to fatigue, and the seat plate or gas cylinder may develop cracks from repeated impacts, leading to decreased sinking stability. Regular inspection of the integrity of the support structure is necessary.

5. Interference from Manual Adjustment Operations
   Some office chairs are equipped with manual height adjustment functions. If the user accidentally touches the bottom control handle (usually located on the right side) and presses down on their center of gravity, the seat will actively descend. This type of sinking is unrelated to the chair's performance and requires confirmation of whether it was caused by improper operation.