Bicycle Mechanics - Simple noob-type question about Presta valve cores

OK, I'm embarrassed to admit it, but I don't know much about replacing valve cores on Presta valves. I have tried a search here but not found the exact answer to my questions.

This morning when I was trying to air up the rear tire on my commuter bike the valve core came out with the pump; after trying hurriedly to fix it I finally had to give up and just drove to work. This has happened to me before -- I've had messed up valve cores on perfectly good tubes but ended up changing the entire tube because I didn't have extra valve cores.

I now have a 10-pack of extra cores on order and on their way to me....

Some questions:

1. Generally, when one is having a problem w/these valve cores, are they defective, or just not properly seated?

2. I ordered a tool for replacing them (why not), but is the tool really necessary? Can I just fasten these in w/something else in my toolbox?

3. Anything else I need to know? I feel like it's a waste to throw away good tubes if the only problem is a loose or defective core...

This shouldn't be happening unless you are pulling off the pump head at an angle. Are you using a floor pump? If so, just be sure you pull the head off straight up. For example, if the stem is at the bottom of the wheel/tire (at the 6 o'clock position), pull it straight up.

I've had the valve come loose maybe twic and both times, I screwd it back in with my fingers.

This shouldn't be happening unless you are pulling off the pump head at an angle. Are you using a floor pump? If so, just be sure you pull the head off straight up. For example, if the stem is at the bottom of the wheel/tire (at the 6 o'clock position), pull it straight up.

I've had the valve come loose maybe twic and both times, I screwd it back in with my fingers.

This morning I was using a Lezyne floor pump (very nice pump, BTW, but I've only used it a few times).

It screws onto the valve for a secure fit, and when I unscrewed it it brought the valve core with it. I don't seem to be able to just press the valve head onto the Presta stem, it feels like it wants to be screwed on.

I know I am about to hear that I was doing this wrong....let me have it....

(Edit: on another forum, I found someone else who had done the same thing w/a Lezyne pump. Because the pump head screws on, you can "unscrew" the valve core when you remove the pump head, if you're not careful. Solution: tighten the valve core, or use tubes w/out removable cores)

OK, I solved my own problem tonight when I got back home and I was thinking more calmly instead of trying to rush out the door.

The valve core was loose; I just tightened it w/my fingers. For extra safety I snugged it up with a small pair of pliers. Then I inflated the tube normally (that is, if anything I do w/a bike could be considered normally). Seems to be fine.

Lesson, as always: Presta valves don't like clumsy people in a hurry.

I thought you might be using a Lezyne pump. I had exactly the same problem, called Lezyne, and was told to put a drop of light oil into the pump chuck. I use Boeshield T9 as chain lube and a very tiny drop of it seemed to have "fixed" my issue for now.

The permanent "fix", of course, is to buy tubes with non-removable valve cores.

Incidentally, I haven't used a pump head that's as nice as a $2 schrader to presta adapter, although plenty try to come up with something better than a thread and o ring...

And my floor pump has a threaded schrader head for some reason, so I'm sorted : )

If you have one of those double-header jobs with a fancy lever or other wanky mechanism, I suggest trying the schrader hole on an adapter for simple and reliable win. Schrader fittings don't mind non-threaded attempts at mating nearly so much...

some Tubes have a removable Presta valve core, many don't.

My Presta pump is a Silca track pump, easy to use , If you don't push it on too far,

there is an unthreaded portion, between the 2 thread types, on the stem.
the rubber gasket, in the air chuck, seals around that.

That's a common problem with the lezyne pumps - that the core will remove with the lezyne head itself. There's a handy plastic tool that you can get to tighten the core, or use a small adjustable wrench.