I have a Continental Road inner tube with a threaded presta valve. I also have a threaded bike pump which I screw onto the valve to inflate the tube.
When I try to unscrew the pump, the uppermost part of the valve unscrews and detaches from the main body of the valve and all the air rushes out.
Is it normal for a presta valve to be separable into two parts like this? How can I prevent this from happening?