The actual total capacity of water that a rubber hot water bag can hold is smaller than the marked capacity. This is a very common phenomenon in the industry. The main reason is not simply due to shoddy workmanship, but is caused by a combination of standards, processes, safety, and structural design:
1. Marked capacity ≠ water storage space
The nominal capacity specified in the national standard is calculated based on the maximum expansion volume of the bag. However, there are several parts that will never be able to hold water
All added together, this usually results in a reduction of 100 to 300 milliliters.
2. Rubber itself will contract and rebound.
When the rubber hot water bag is produced, it is formed by a mold. After cooling, it will slightly contract.
- The mold size is made according to the nominal capacity.
- The actual inner cavity of the finished product will be slightly smaller.
- The thinner and softer the rubber is, the more obvious the shrinkage difference will be.
3. The manufacturer deliberately made it smaller for safety reasons.
The hot water bag is filled too full, and the hot water will expand and easily burst the bag or leak.
Many factories deliberately make the inner cavity a little smaller to prevent users from filling it with too much water and causing danger. This is a passive safety design.
4. Cost and Process Control
- The tolerances for rubber extrusion, vulcanization, and bonding inherently have errors.
- To ensure the qualification rate, manufacturers usually will reduce the size downward. They would rather make it smaller rather than larger.
- Making it larger is prone to uneven thickness and insufficient pressure resistance.
5. Different measurement methods
- Marked capacity: Theoretical maximum volume
- Your actual measurement: It can only be filled to the lower edge of the bottle mouth. Any higher and it will overflow.
There is a fundamental difference between the two.
Summary in a nutshell
The actual capacity is less than the marked value, mainly due to:
Structural occupation of space + rubber contraction + safety margin + process tolerance
The normal difference is generally within 100 to 300 ml and is considered a common situation.
