An assembly method of an apparatus suitable for pressurized liquid transfusion is disclosed. In one step, a nozzle is to be inserted into the through hole of an elastomeric ring. Because the dimension of the nozzle is larger than the through hole, the internal wall of the elastomeric ring is tensioned and deformed so as to fit the nozzle. In one step, the elastomeric ring along with the nozzle is inserted into a receptacle. The dimension of the outer contour of the elastomeric ring needs to be decreased so as to be accommodated by the receptacle. Due to the flexibility of the elastomeric ring, it resumes at least partially to its original shape. Therefore, proper seal is created and maintained between the elastomeric ring and the nozzle such that leakage and pressure loss may be prevented. The foregoing is capable of working under high-pressured environment for prolonged use.