Why doesn't the air pipe of the medical infusion set flow liquid, while the vertical downward pipe flows?
Jun 27, 2022
1、 Evolution of intravenous infusion methods
The intravenous infusion system has developed to the third generation. The upper part of the first generation liquid container is completely open, which is in direct contact with air, and there is a great safety risk. In the second generation, the upper end of the liquid container is closed, and the air pressure inside is balanced through the air inlet pipe. The third generation is completely closed, but the liquid container is changed to a soft bag.
2、 Principle overview
In order to achieve the purpose of downward flow of liquid medicine, the condition must be met at the intravenous needle T1: the downward force on the liquid must be greater than the upward force, that is (top gas pressure P1 + upper hydraulic pressure P2) > venous pressure P3.
In the first generation infusion system, P1 is equal to atmospheric pressure; In the second generation infusion system, P1 can also be ensured to approximate atmospheric pressure through the air inlet pipe; In the third generation infusion system, although there is no air on the upper part of the container, because the liquid container is changed into a soft bag, the liquid in the container also receives 1 atmospheric pressure through the bag wall. Because P1 is relatively fixed, the height of the container can be adjusted by changing P2, so as to achieve the purpose of drug liquid flowing down.
