2 in the last 4 months, one on the road and one at home.
You can tell the valve core has failed when trying to inflate the tube.
It has become a rubber lung: pump air in, exhale air out, pump air in, exhale air out while your pump pressure gauge keeps returning to 0.

Anyone have any hacks to fix the failed valve core, besides replace the tube, that you have actually successfully implemented?
Don't need untried suggestions.

Um... The value that ensures one-way air flow is located in the pump. As long as the pump head is attached to your tube valve, the tube valve is supposed to stay open the whole time. It is not supposed to act as a "valve" when you are pumping up your tube.

So, if you observe this "rubber lung" effect when you attempt to inflate your tube, it is your built-in pump value that failed, not the valve core in your tube.

A drop of loctite on the valve core threads, then twist down tight.

Yes, this occurs. wphamilton has a good solution. You can sometimes also just tighten them by hand and it is enough to get you home. Beeswax is good too.

Other recent problems with valvestems include stems that will not accept a valve adaptor and stems that defy attempts to inflate with any make or style of handheld pump. Guess they assume we are all. using CO2

Best hack!

The Lezyne Carbon Drive mini-pump has a "tool" on the end of the hose that you can use to tighten up the valve core out on the road and before you attach the chuck to inflate the tube.


https://ride.lezyne.com/collections/...mp-cbrdr-v3m05

Why do they even sell inner tubes with removable inner core? Seems like there is no advantage to their use.

Probably because it is more practical to manufacture the core separately and just put a threaded hole in the valve stem to mount the core. It also allows replacement; I have had cores leak and just replaced them; if they were not replaceable the whole tube would have had to be replaced. A removable core also enables installing sealants. I have valve caps with core tools built in which makes routine tightening quick and simple. https://smile.amazon.com/Suriel-Meta.../dp/B01M357RW6

For valve extenders for use with deep section wheels

Your theory doesn't hold air.

Tried inflating using a 2nd pump. Same results.

Installed a new tube, used 1st pump to inflate the tire to 90 psi. No problems.

Apparently, your pumps were manufactured in some alternative parallel universe of some kind, where the process of inflating a tube relies on the valve in the tube itself. In our universe we don't even need a core in order to inflate a tube: it will inflate perfectly fine, provided the built-in one-way valve at the base of the pump is working properly.

It is unbelievably bizarre that your pump somehow managed to draw air from the tube on the backstroke. All pumps have a built-in valve intended to prevent exactly that.

As above, this is a weird one.

When using Schrader valves, the pump chuck pushes the valve core in and holds it open. The bottom of the pump and the tube are all one volume of air until you take the chuck off the valve, otherwise the gauge wouldn't be able to read the pressure. The one-way valve in the pump keeps the air from escaping or pushing the pump piston back out. With a properly working pump you should be able to pump all the air you need with no valve core at all.

Question:

When pumping, does the pressure jump very high in one stroke, then drop back to zero? because that is a symptom of the valve not opening, not a symptom of the valve being stuck open.

My 2nd pump was a Zefal, who have been making presta pumps for 100+ years.

Pressure remains low with one stroke as I can see the tube inflate slightly.

You can try pumping your tube with no valve core to see if your theory holds.

You can absolutely pump a tube up without a core in the valve. I have done it.* Of course the air escapes as soon as you remove the pump, but the pressure will remain while you are pumping, What you describe is 100% not the valve core getting stuck open.

*During the winter months working in bike shops, you sometimes get desperate for something to do.

That would depend on the kind of valve. Schrader valves have to be held open to get air in the tube. Presta valves are check valves with a low cracking pressure. Air goes in and the valve closes once there is a pressure differential between the air supply and the pressure in the tube. A Presta valve is supposed to act as a valve when air is being added.

Yes, in both types. Schrader valves have always had removable cores. Many Presta valves now come with removable cores. The Presta ones are for adding sealant to tubes (and for tubeless systems).

You haven't said which type of valve you are using but the solution is the same...get a core remover and tighten up the valve. Or just get a new tube.

While presta valves do close when there is pressure in the tube greater than whatever is on the other side of the valve, this isn't necessary while pumping. The chuck is the only thing difference between presta and Schrader pumps, and the only difference there is that Schrader pumps manually push in the valve core to open it. The pump will still have a check valve that keeps air from flowing back in.

True. I assume we are talking about a Presta valve here (although this makes no difference if a bicycle-specific pump is used).

Absolutely not. As you correctly stated above "valve closes once there is a pressure differential between the air supply and the pressure in the tube". But because of the built-in one-way valve in bicycle pumps, once you start pumping there will be no pressure differential between the tube and the pump hose. I.e. there's no pressure differential across the Presta valve. As long as the pump head is securely attached, Presta valve remains "free floating", "unloaded", "loose" or permanently open. Some bicycle pumps (e.g. some Lezyne models) are actually designed to apply direct mechanical pressure on Presta valve's head to positively ensure that it remains permanently open. But most pumps just rely on the absence of pressure differential across Presta valve.

The pressure differential exists across the one-way valve built into the pump. There's no pressure differential across the tube valve. That is if the pump is working properly.

If your Presta valve actually "acts as a valve when air is being added" using a regular bicycle-specific pump, it means that there is something wrong with your pump: either the pump's built-in one-way valve is broken, or there's a leak somewhere on the path from the pump's valve to Presta valve.

A small leak is typically OK. But if the tube is acting as a "rubber lung" (per OP's description), i.e. all air pushed in on forward stroke gets evacuated at backstroke, it immediately means that the pump is hopelessly broken. The valve core could be broken as well, but that would be a secondary problem.

To illustrate it even further: if the pump is working properly, you can completely remove the core from a Presta valve. And you should still be able to successfully pump up the tube to whatever pressure you want. (It will be difficult to keep air in the tube once you detach the pump head, but that's a different story.) There should be no "rubber lung" effect even with the core completely removed.

700c tube with removable presta valve core.

That makes sense. Thank you.

Thank you, that makes a whole lot of sense.

1) Easy instillation of sealant
2) Easy replacement of damaged core, e.g. bent or broken stem nut
3) Addition of stem extenders for deep profile rims

So put a new core in. I buy them by the ten bag, and go through about half a bag a year. Most times, the little rubber cone at the very bottom of the valve core works itself loose and jams inside the body of the core. Instant non-working valve.

Yes, a Presta valve opens when the pressure inside the pump is higher than the pressure inside the tire. But as soon as that pressure changes...and, assuming a manual floor pump, it does when the pump handle is pulled up...the pressure inside the tube is higher than the pressure in the hose and the valve closes and traps the air in the tire.

A Schrader valve has to be held open for air to flow into it. You could overpressure the valve and get it to open but you need something on the order of 25 psi higher than what is in the tube to do so. You have to overcome the spring on the valve which is keeping the valve closed.

And the differences aren't just the chuck. The chuck is different because the valves are different. You could hold a Presta open like a Schrader but that defeats the purpose of the check valve.

44.5mph doesn't say what kind of pump or tube or chuck is being used. I would almost assume a Schrader rather than a Presta since a Presta would close if the pump has a problem. If the valve on the Presta is loose, then it would also leak.


Yes there is a pressure difference between the tube and the pump hose. Once you pull up on the handle, the check valve in the pump seals so that the pump handle can be pulled up to fill the chamber with air. But it takes a small pressure differential for the pumps check valve to seal. A little bit of the air in the hose will leak back into the pump shaft. The pressure in the hose decreases slightly and a Presta valve will close. The cracking pressure on a Press valve is very small. The seal between the hose and the valve may not be perfect as well which causes a decrease in the pressure. Even the best pumps still leak a bit of air at the valve seal.

I have not seen any Presta compatible chucks that actually hold a Presta open. All of the ones from on-bike to floor pumps chucks I've seen have open structures that ensure nothing touches the end of the Presta valve. Holding the valve open would defeat the purpose of the check valve.



There is always a leak somewhere with just about every pump I've ever seen. They simply aren't that tight a system. And, as I said above, the pump's check valve...which is really what the "one-way valve" is...has it's own cracking pressure which reduces the pressure in the hose slightly but still enough to close the Presta valve.


I didn't say that the pump isn't broken. However, a Presta valve wouldn't pulse back. The pressure difference would cause it to close. Air would go in but it wouldn't come back out.

Generally the difference is just the chuck - otherwise how could pumps come with a chuck that works with or can be adapted to work with both valve types? The little switch on the chuck of my cheap pump does not effect the way the pump functions at the other end of the hose, it just changes which hole in the chuck is connected to the hose.

And while you are correct in the way presta valves work and keep air from escaping, this function is not necessary during pumping as all reciprocating pumps have a built in check valve - if a pump didn'n have a check valve then it would simply be called a 'piston' and it wouldn't be able to push air into a tube and have it stay there.

The reason that chucks have either a different hole or a different configuration is because of the nature of the valve. Yes, the pump has it's own check valve but that check valve allows for a small amount of pressure change in the hose. Since the Schrader valve is held open, that doesn't matter for that valve. But for a Presta valve, the change causes the valve to close. Pressure introduced when the piston in the pump is pushed down causes it to open again. It goes through a cycle of opening and closing.

I'm not saying that the pump doesn't have a check valve. I'm saying that the Presta valve closes at a very low pressure differential. Most all hoses leak some air around the valve stem. This can be because valve stems have threads or because of a poor fit but nearly all of them leak some air. For a Schrader valve, that leak is coming out of the tube. For a Presta, the valve closes until the pressure outside the tire is higher (by a very small amount) than inside.

The chucks have to be different because of the way that the valve has to be used.

Buy Michelin standard tubes.. they don't have removable cores, and their valve stems (brass I think) are much more durable than some other brands who use some sorta flimsy alloy that does bend and break more often.