Office Chair Hydraulic Rod: Class 3 vs. Class 4

The core differences between Class 3 and Class 4 hydraulic rods for office chairs lie in safety certification levels, tube wall thickness, load-bearing standards, and costs. For daily use, users weighing ≤125kg can opt for Class 3, while those who are heavier or have higher safety requirements are advised to choose Class 4.

Safety Certification Level and Markings

According to international industry standards, pneumatic rods must pass BIFMA testing and certification, with the grade marked as a steel stamp on the outer tube. Class 3 pneumatic rods are marked as Class 3, and Class 4 as Class 4. Class 4 represents the highest safety level in the industry, requiring more rigorous burst pressure testing (e.g., Class 4 must withstand higher instantaneous air pressure impacts), while Class 3 has relatively lenient testing conditions. This difference directly affects safety in extreme situations; for example, Class 4 pneumatic rods, with thicker tube walls, offer better resistance to gas leakage or explosion risks.

Tube Wall Thickness and Compressive Strength

Class 3 pneumatic rods have an outer tube thickness of 1.8 mm and an inner tube thickness of 2.0 mm; Class 4 rods have an outer tube thickness of 2.0 mm and an inner tube thickness of 2.5 mm, with tube walls approximately 10% to 25% thicker. Theoretically, Class 4 pneumatic rods can withstand higher air pressure impacts, reducing the probability of accidents caused by tube wall deformation. However, in regular use (with a load ≤125kg), the safety performance of both types of pneumatic rods is similar, with differences only becoming apparent under overweight or long-term high-pressure conditions.

Load-Bearing Standards and Durability Testing

Class 3 pneumatic rods must pass 80,000 lift cycle tests under a 100kg load, with a safe load capacity of 125kg and an ultimate load capacity of 250kg; Class 4 rods must pass 120,000 tests under a 122kg load, with no structural damage (e.g., seal ring rupture or gas leakage) after testing. The testing standards for Class 4 are more stringent, but in actual use, if the user's weight does not exceed 125kg, the durability difference between the two is not significant; for weights exceeding 125kg, Class 4 pneumatic rods offer better long-term stability.

Cost and Market Strategy

The purchase price of Class 4 pneumatic rods is only about 50 yuan higher than that of Class 3, but the retail price may double, with profit margins generally 30% to 50% higher, making them a major profit point for merchants. This premium is partly due to safety certification costs and partly due to market positioning differences.

Purchase Recommendations

• For users weighing ≤125kg, Class 3 pneumatic rods are fully sufficient, and there is no need to pay a premium for Class 4.
• For users weighing >125kg or in special scenarios (e.g., gaming chairs, gyms), prioritize choosing Class 4 pneumatic rods, but ensure that the load-bearing capacity of other chair components (such as nylon footrests and PU wheels) matches.
• When judging the quality of pneumatic rods, check for steel stamp markings (e.g., Class 3/4 and SGS, TUV certification marks) and be wary of low-priced products (the risk is higher for entire chairs priced consistently below 200 yuan or individual pneumatic rods priced below 40 yuan).