How to keep Presta valve core from detaching after inflation?

Question

I have Presta valves on my bike tires and for the rear tire, each time I inflate the valve, upon detachment, the core screws off with the pump attachment and the tire deflates. I tried about 6 times, no luck.

Here are pictures of the detached pump connector with Presta core detached and the valve stem with no core:

What am I doing wrong? How can I inflate and detach the pump without detaching the insert? I had no issue with the front tire. Is the valve broken or am I doing something wrong?

Answer 1

I've had this happen with some tubes - Continental, maybe? Conti tubes are compatible with valve extenders, so the valve on them does come off like this. You're probably screwing the chuck on too tightly, and then the valve comes off with it.

Or maybe some tubes come with the valve not properly torqued.

And after it did come off, you probably didn't tighten the valve tight enough into the stem to stop it from happening again. There should be small flats on the side of the valve portion that comes off - you need to use a wrench on that when you rescrew it into the stem. Be sure to hold the stem with a pair of pliers when you do this to prevent the stem from twisting. If you don't you can tear the tube.

Worst case, put Loctite on the valve threads if it keeps happening.

Answer 2

1. Hand tighten or use needle pliers to attach the inner core in the valve.
2. Remove the rubber from the presta to schrader adapter. Now it won't apply as much torque when you remove it, and the inner core will stay put. Some air will escape as you are pumping, but that's ok. Use soapy water to reduce friction between the adapter and valve stem.

Answer 3

I also use a pump with a screw-on head and have had this happen. It's annoying.

1. It would be a good idea to get a valve-core tool for reinserting the core and tightening it down. Some multi-tools have valve-core tools in their arsenal. In my experience, pliers don't do a great job.
2. You can use thread-locker (such as Loctite) to secure the core so it doesn't come back out.

Answer 4

You have a presta stem where it's possible to add stem extensions to increase stem length. You are removing the Presta's main valve body from the factory stem because the manufacturer leaves these incompletely torqued for whatever reason. You also appear to be using an adapter (the silver piece with gasket in your photo) that attaches to the presta valve, converting it for use with a pump set-up for Schrader valves. When one unthreads this adapter (all the ones I've dealt with screw on, they can't just be pushed on), if you've torqued the adapter greater than the torque of the valve body, the valve body threads to the stem will yield first, the adapter stays on the valve body, and the next thing you hear is the hiss of air. That gasket also contributes to the problem by gripping the valve body.

First, there are typically wrench flats on the valve body. Sometimes in the threaded area. Yours are likely to be found at that gap in the threads of the valve body. Reinsert the body and hand tighten it. Often times the max torque you can achieve with your fingers is tight enough to keep the body in place while using and removing the adapter. A spoke wrench's 12 gauge slot fits the valve's flats and is perfect to snug it up so it doesn't come off with the valve adapter. Needle nose pliers work well too. Use care not to over-torque the valve body and damage threads. Also, in a tubeless set-up watch that the whole stem doesn't turn which will turn the rubber gasket inside the rim. Some of these are positional--they fit in one direction within the rim well. Somebody's idea of loctite isn't a bad idea, but I wouldn't purchase any for this task.

Part of my airing up process is giving the valve body a firm twist right to check tightness between removing the cap and opening the valve. I'd also suggest to put the adapter on the opened stem first, then attaching the pump to the adapter to better gauge and control the torque at the stem-adapter interface. IDK it's a minor point and may work better the other way. I typically use an air chuck you push onto the adapter to get air--same as filling a car tire. The key to it all is not getting the adapter tighter than the valve body. Many bicycle pumps these days have ends that are themselves adaptable to either Schrader or Presta valves using the same parts of the connecting end configured in different ways. See if that's possible with your pump, set it up for Presta and eliminate the adapter.

Answer 5

Please look at the following video:

Basically, you removed the wrong bit or it was removed before. There are two parts to the presta valve, they main valve that is attached to the bit that sticks out of the wheel and the valve opener.

You need to leave the whole thing attached to the tube but unscrew the valve to just open it, but not remove it from the tube.

If you look at the video, you'll see it easier.