The glass tube has a graduated scale of 5 mL increments and seals against the inner end pieces. A springloaded valve made from titanium is located in the center of the movable seal. When Superloop 150 mL is in loading position, the valve is closed and remains closed during sample loading. When the sample is injected onto the column the seal moves downwards. When the bottom position is reached, the pressure increase causes the valve to open and the buffer to pass through the valve.