The principle of vacuum blood collection is to draw different vacuum degrees in advance from the tube with a cap, and use its negative pressure to automatically and quantitatively collect venous blood. One end of the blood collection needle is inserted into the human vein, and the other end is inserted into the rubber plug of vacuum
blood collection tubes
. Under the action of negative pressure, the blood collection needle is pumped into the blood container of human venous blood in the vacuum collection vessel. Under a single venipuncture, multi-tube collection can be realized without leakage. The volume of the inner cavity connected to the blood collection needle is very small, and its influence on the blood collection volume can be ignored, but the probability of reflux is relatively small.