medical infusion set not flow out of liquid, while the vertical downward tube flows?
intravenous infusion system has been developed to the third generation. The upper part of the liquid container of the first generation is completely open and directly in contact with the air, which has a greater 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. (Refer to Figure 1)
2. principle overview
, in order to achieve the purpose of downward flow of liquid medicine, the condition must be met at the venous 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 be ensured to be similar to atmospheric pressure through the air inlet pipe; in the third generation infusion system, although there is no air in the upper part of the container, the liquid in the container is changed to a soft bag, and the liquid in the container is also subjected to 1 atmosphere through the bag wall. Since P1 is relatively fixed, P2 can be changed, that is, the height of the container can be adjusted, so as to achieve the purpose of liquid medicine flowing down.
the problem comes, it is also the two thin pipes connecting the lower part of the container. Why is the air flowing in the air inlet pipe while the other one is the liquid medicine? How does the air in the air inlet pipe enter the container?
3. those things about the intake pipe
(I) Intake Pipe Structure
intake pipe actually has a very subtle design. The sheet in the middle allows air to pass freely, but it will block the outlet under the pressure of the liquid from the inside to the outside. The function is to allow air to enter and exit freely, but it can prevent the liquid from passing (the pressure is too high Except when). It is such a design that ensures the perfect operation of the second-generation infusion system. (Refer to Figure 3)
(II) physical process
second-generation infusion system is working, the intake pipe actually changes three states in turn: full of liquid medicine, liquid medicine reflux, and air circulation.
1, filled with liquid phase
When the tip of the infusion set is inserted into the container, under the action of P1 and P2, the liquid medicine will overcome the lower resistance and flow downward along the air inlet pipe and the infusion pipe respectively. Because the infusion set switch is usually closed before injection, the liquid will enter a part of the infusion tube and fill the intake tube.
2. Liquid medicine reflux stage
point T2 is subjected to inward outside air pressure P0 and outward P1 P4. After the infusion switch is turned on, as the liquid medicine overcomes the venous pressure and enters the patient's body, the gas in the upper container gradually decreases due to the increasing volume. When P1 P4
3. Vent air phase
, when the liquid medicine in the air inlet pipe flows back to T3, the outside air moves further to the inside of the container under the action of the pressure difference. At this time, the air encounters a new outward resistance, that is, the surface tension of the liquid. As the air moves inward, the liquid surface is pulled inward into a semicircle and an ellipse until it completely overcomes the surface tension and becomes a closed bubble. The upper and lower surfaces of the bubble are subjected to two forces with different sizes and directions due to the height difference of the liquid, and finally an upward resultant force is generated, which guides the bubble to move up to the top air area, and P1 increases accordingly, completing a cycle.
