Removable valve core failures
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. :deadhorse: 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.
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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 |
Originally Posted by wphamilton
(Post 21128079)
A drop of loctite on the valve core threads, then twist down tight.
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.
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Originally Posted by eja_ bottecchia
(Post 21128144)
Why do they even sell inner tubes with removable inner core? Seems like there is no advantage to their use.
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Originally Posted by eja_ bottecchia
(Post 21128144)
Why do they even sell inner tubes with removable inner core? Seems like there is no advantage to their use.
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Originally Posted by AndreyT
(Post 21128049)
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. Tried inflating using a 2nd pump. Same results. Installed a new tube, used 1st pump to inflate the tire to 90 psi. No problems. |
Originally Posted by 44.5mph
(Post 21128285)
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. 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. :thumb: |
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. |
Originally Posted by AndreyT
(Post 21128049)
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.
Originally Posted by eja_ bottecchia
(Post 21128144)
Why do they even sell inner tubes with removable inner core? Seems like there is no advantage to their use.
Originally Posted by 44.5mph
(Post 21128285)
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. |
Originally Posted by cyccommute
(Post 21128336)
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.
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Originally Posted by cyccommute
(Post 21128336)
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.
Originally Posted by cyccommute
(Post 21128336)
A Presta valve is supposed to act as a valve when air is being added.
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.
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Originally Posted by redlude97
(Post 21128264)
For valve extenders for use with deep section wheels
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Originally Posted by dsbrantjr
(Post 21128171)
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
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Originally Posted by eja_ bottecchia
(Post 21128144)
Why do they even sell inner tubes with removable inner core? Seems like there is no advantage to their use.
2) Easy replacement of damaged core, e.g. bent or broken stem nut 3) Addition of stem extenders for deep profile rims |
Originally Posted by 44.5mph
(Post 21128396)
700c tube with removable presta valve core.
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Originally Posted by Wilfred Laurier
(Post 21128342)
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.
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.
Originally Posted by AndreyT
(Post 21128375)
True. I assume we are talking about a Presta valve here (although this makes no difference if a bicycle-specific pump is used).
Originally Posted by AndreyT
(Post 21128375)
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. 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.
Originally Posted by AndreyT
(Post 21128375)
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.
Originally Posted by AndreyT
(Post 21128375)
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. |
Originally Posted by cyccommute
(Post 21129110)
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. 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. |
Originally Posted by Wilfred Laurier
(Post 21129118)
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.
Originally Posted by Wilfred Laurier
(Post 21129118)
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 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.
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