Hey all, I was riding my road bike over a fairly rough trail, and the back tyre started to deflate. I tried to reinflate the tube but no air got into it. A passing cyclist stopped to have a look and said the valve stem had partially detached from the tube. He suggested i had no option but a new tube. A friend came out to where I was with a new tube, fitted it, inflated it and I completed another ride of a couple of hours. However, as I tried to cycle to work this morning, the tyre remained at a low pressure and then about half a mile down the road deflated completely. This time the tyre is allowing air in, but it does not stay there. I cannot see any obvious puncture. It seems odd that a similar thing should happen with two different tubes within the space of two different days. Bit frustrating, just as I was getting into cycling to work as well.. Any ideas?