Ok, I was checking a new tube, to learn why I was having difficulty inflating it.

The grooves on the stem were not as deep as I'd like, but I did get the Serfas FMP-500 to attach to the tube's Presta valve. When I tried to inflate the tube, I didn't get any reading on the pump's dial. The tube did get larger in places, but not uniformly. Then the bloody thing exploded. Pow, a chunk of it blew off!

Before I go thru my whole stash of Serfas tubes, can anybody say what may have caused the first one to explode?

Tubes often inflate non-uniformly when they are inflated outside of a tire due to small variances in thickness and elasticity throughout the length of the tube. Inside the tire the tube inflates as one would normally expect it due to the resistance of the tire to the tubes expansion.

Your pressure gauge did not show a reading because the tube by itself was not gaining a significant amount of pressure despite the increasing volume of air inside it. Again, inflating it within a tire will give the resistance to expansion while inflating to register on your pump's pressure gauge.

Your exploding tube is relatively the same as overinflating a birthday balloon...there is a large volume in the balloon but not a lot of pressure. When the expansion ability of the elastic material is exceeded the material fails.

Easy solution...don't repeat what you did with your first tube. If you have presta valve tubes then ensure the tiny knurled nut at the tip of the valve is unscrewed all the way and then manually depress it to ensure it is not sticking in position. Also, as you attach your pump be careful not to bend the thin stem the tiny nut is attached to that moves within the valve.

-j

J,

Thanks so much for replying. I wondered if something like that could have been happening, but hadn't ever seen it discussed. Love the balloon example; easy for this technoignoramus to understand.

I have bent a valve in the past, and can see the bend in one which has a 60mm stem. The new tubes have 48mm stems, so it should be easier to not bend them. (The 60mm was all the shop had at the time.)

Fog

So just to clarify a couple things...
1. The "stem" I was referring to is the metal piece that moves up and down to open/close the valve of the tube...it is the piece within the portion of the valve that you are refering to as a stem. I gather we are both using the term correctly but just wanted to clarify to avoid potential for confusion.

2. The longer the section of the valve stem that is unsupported by the rim, the easier it is to bend or break, or even rip the entire valve off the tube. This becomes even more of an issue when using a frame pump to inflate...but I looked up the pump you used and found the Serfas FMP-500 is a floor pump...in this case the recommendation would be to ensure the valve nut is loosened completely and manually manipulate the inner stem to ensure it moves freely and then exercise caution when attaching/removing the pump to avoid damage to the valve.

3. One last thought...the valve only needs to be inserted into the pump head enough so that a seal is made around the valve and the pump head does not blow off the valve while pumping. Jamming the pump head too far on the valve can sometimes cause damage or problems with inflation. If the pump head does not stay put while pumping, enouraging you to press it on the valve further, then I recommend replacing the pump head insert and/or using a length of velcro strap connected to the head wrapped around the tire/wheel to keep the head in position while inflating.

Good luck.

-j

Yes, we are. Understood, thanks.

Been there, done that. Thanks again.