Reasons for different valve standards / advantages??

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Tangled Metal
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Reasons for different valve standards / advantages??

Postby Tangled Metal » 31 Jul 2020, 9:34pm

There's a few valve types and people probably have their favourites or reasons to use one over another. This is a twofold query.

Why did the different valve standards develop / what are the reasons for them?

What are the advantages / disadvantages of them?

I use presta and Schrader. AIUI one is typically used for higher pressure / narrow tyres, the other for other tyres. I still don't see why Dunlop or woods are still around but that's possibly down to my ignorance. So I'm seeking enlightenment on this, hence my questions.

Jdsk
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Re: Reasons for different valve standards / advantages??

Postby Jdsk » 31 Jul 2020, 9:40pm

Brandt's short article, with hyperlinks
https://www.sheldonbrown.com/brandt/presta-schrader.html

Jonathan

Brucey
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Re: Reasons for different valve standards / advantages??

Postby Brucey » 31 Jul 2020, 10:38pm

Woods/Dunlop; because that was the only game in town to start with. It has the virtues that you can remove/fettle the valve core and deflate the tyre fully and instantly using your fingers alone, and it is possible to have a low pumping force, with no sprung/locked valve mechanism. Simple/cheap pumps (with flexible connectors and no check valves) are rarely perfect but can work well enough with this valve design. Small leaks in the connection are tolerated, in that whilst the tyre won't be pumped up quickly, it won't be busy going flat through a small connector leak either.

Schrader; requires a more complex and leak-prone connector and also uses a more complex pump which must have a functional check valve in it. There is no tolerance for leaks in the connection; any leak results in your attempt to inflate the tyre being more likely to deflate it. The connector must open the valve fully else you won't get any air into the tyre. The valve core is held shut by a spring, which means that it is more likely to leak than presta if it gets dirty but can't so easily fettled like woods. You need tools to remove the valve core and full deflation without removing the core is pretty tedious work. On the plus side it fits wherever you might otherwise use a woods valve and you can use pumps etc meant for car tyres.

Presta; allows easy pumping, and the locking mechanism in the valve core makes sealing reliable. You can use a simple pump (with no check valve) and the connection tolerates small leaks much as woods does, but getting a good seal is easier because of the stem design. The narrow valve body fits easily into narrow rims and the valve is lighter and more compact than other types. Full deflation is easy. On the downside the locking part of the valve can be damaged and the sort with a removable insert causes problems with pumps that connect by screwing onto the valve.

Most modern pumps work well enough with Schrader (when they are in perfect condition) and presta (even when they are not), but may seal least well with woods. However if you are stuck with simpler pumps for some reason (eg they are the only ones that fit your bike) or you value being able to fettle the valve without tools etc then woods may still be the best choice for a utility bike. For everything else I prefer presta; I do have bikes with Schrader valves in though, mainly because of their ubiquity rather than their intrinsic quality/utility.

cheers
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mjr
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Re: Reasons for different valve standards / advantages??

Postby mjr » 31 Jul 2020, 11:01pm

Schrader is a rubbish alternative to Woods. If there was any sense, Schrader would be the least common one.
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francovendee
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Re: Reasons for different valve standards / advantages??

Postby francovendee » 1 Aug 2020, 7:38am

Never had a problem with Schrader valves but bent Presta when attaching the pump on two occasion.

Marc
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Re: Reasons for different valve standards / advantages??

Postby Marc » 1 Aug 2020, 7:53am

mjr wrote:Schrader is a rubbish alternative to Woods. If there was any sense, Schrader would be the least common one.

So, why do cars, trucks and even passenger aircraft (200bar tire pressure on the Airbus A380!) use the "inferior" Schrader valves? :lol:

Schrader valves just work! And they work reliably even with 20-60x the tire pressures we use on our cycles. Not to mention, that Dunlop/Woods valves don't allow to check tire pressure...

Jdsk
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Re: Reasons for different valve standards / advantages??

Postby Jdsk » 1 Aug 2020, 8:32am

Thanks, Brucey. I was looking forward to seeing your conclusion.

In response to the original question I'd just add that the persistence of technology standards often owes a fair bit to geography and history and politics and commercial advantage as well as the inherent advantages and disadvantages.

Jonathan

Jdsk
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Re: Reasons for different valve standards / advantages??

Postby Jdsk » 1 Aug 2020, 8:33am

Marc wrote:So, why do cars, trucks and even passenger aircraft (200bar tire pressure on the Airbus A380!) use the "inferior" Schrader valves?

"Valve Cores in Aviation Applications"
http://acversailles.free.fr/documentation/08~Documentation_Generale_M_Suire/Train_d%27atterrissage/Pneus/Valve_cores_in_aviation_application.pdf

Jonathan

Brucey
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Re: Reasons for different valve standards / advantages??

Postby Brucey » 1 Aug 2020, 9:52am

I should have anticipated the usual 'Schrader valves work so well on cars, aircraft etc, so they must be *perfect*...' type comments. Well they do, sort of , but they are not at all the same thing as Schrader valves as are found on bicycle tyres. They are also a long way from perfect.

Schrader valves in different applications may look the same to the uneducated eye but the inserts are different for different applications. Under no circumstances should you think of swapping a bicycle Schrader valve core into a car tyre; the spring in it may not be adequately strong/reliable and the tyre may spontaneously deflate when the car is driven at high speed. I expect there are similar issues with aircraft valves.

What Schrader valves definitely do is make it necessary to have a more complex pump (which must be in perfect condition) if you want to inflate them. And you must use tools if you want to remove the valve core. Both these requirements are antithetical to the usual ones considered appropriate for utility bicycles; Woods valves are still widely used in the Netherlands for example.

Schrader valves on bicycles should be fitted with dustcaps; otherwise they become the type of valve that (having the widest opening) is most likely to become contaminated with dirt, and the least easy to clean/fettle back into working order.

I am a little surprised that the Schrader design has not been displaced (in cars, aircraft etc) by "something better". The reason I say this is that the main thing keeping the air in tyres with a Schrader valve is a shonky little spring which is holding the valve core shut; this spring has to resist opposing forces which amount to tens or even hundreds of g when the wheel is turning at speed. In general terms you wouldn't get away with designing something safety critical in that way these days, it isn't usually allowed for a spring that might fail to be the main thing between you and disaster.

The sticking plaster for this crappy design is the (widely ignored) stipulation that you should use a dustcap with a Schrader valve on car, motorcycle and aircraft tyres. This is a safety feature; it is intended to provide a secondary air retention seal in the event of valve core failure. However between dustcaps where the seal is so badly made it cannot work, damaged plastic dustcaps, badly fitted dustcaps, and missing dustcaps, problems with this secondary air seal are commonplace. Next time you hire a car, check for dustcaps; it is SOP amongst lazy hire car operatives to leave them off; it is only a matter of time until they are sued by someone sharp enough to realise that this contributed to their accident.

I hope that clears up a few misunderstandings about Schrader valves.

cheers
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mercalia
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Re: Reasons for different valve standards / advantages??

Postby mercalia » 1 Aug 2020, 10:03am

francovendee wrote:Never had a problem with Schrader valves but bent Presta when attaching the pump on two occasion.

me 2. with Presta I have found the unscrewed head can interfer with pumping, unscrewed too much and it wont inflate, or even deflates the tyre when you insert the pump due to the pumps rubber seal..., have to unscrew just a certain amount or it wont. tedious. Never any problems with Schrader. And the caps are better more solid. As for removing the insert I havent done it often but I have some times tightened one up - the tool is hardly rocket science - I have seen some of caps that have the tool on the other end and I have one with a prong to deflate them

100_7355.JPG



cheap enough

https://www.ebay.co.uk/itm/Schrader-Valve-Core-Puller-Removal-Tool-Thread-Repair-Motorcycle-Motocross/402334908713?hash=item5dad078129:g:LhYAAOSwTnhfAGea

or you can from ebay get metal caps with the tool on the other end

https://www.ebay.co.uk/itm/4-Top-Quality-Schrader-Metal-Dust-Caps-with-Valve-Remover-Tool-for-Cars-Bike-Van/232565429670?hash=item3625fad5a6:g:N1IAAOSwnI9cfOsi

these have an insert at the end so you can get a good secondary seal. 4 for £2


I thought it was the pressure in the tyre that was keeping the Schrader valve closed. I cant believe the ( plastic) dust caps are a secondary (air tight) seal, they would need to be metal with a rubber insert at the end like the above ones?
Last edited by mercalia on 1 Aug 2020, 11:05am, edited 11 times in total.

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Audax67
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Re: Reasons for different valve standards / advantages??

Postby Audax67 » 1 Aug 2020, 10:16am

Funny: I only learnt of Woods valves yesterday. When I was growing up they were just bike valves, and you had a length of spare valve rubber in your Dunlop Long Cycle Repair kit. That someone might have invented them never crossed our minds, and woods were something you built furniture with.
Have we got time for another cuppa?

Brucey
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Re: Reasons for different valve standards / advantages??

Postby Brucey » 1 Aug 2020, 10:53am

mercalia wrote: with Presta I have found the unscrewed head can interfer with pumping too much and it wont inflate, or even deflates the tyre when you insert the pump, have to unscrew just a certain amount or it wont. tedious.


don't use a hand pump with a screw-on presta connector. Buy a decent pump, learn how to use it correctly (you don't need to push it on that far.... :roll: ) and you won't have 'problems' with presta.

Never any problems with Schrader. And the caps are better more solid. As for removing the insert I havent done it often but I have some times tightened one up - the tool is hardly rocket science -


no tool is 'rocket science' but this is scant consolation when you don't have one by the side of the road when you need it. FWIW the dustcaps with the tool built in are at best, suitable for tightening a loose insert (*) and then not always. They won't reliably remove inserts which are properly tight.

(*) which is more common than you might expect. I've seen whole batches of inner tubes with loose/leaky inserts in Schrader valves. They all had to be tightened, every single one and a dustcap with the tool on wouldn't do the job.

BTW dustcaps for presta are exactly that; merely to keep dust out; they are (unlike Schrader) not intended to provide a means of secondary air retention. They don't need to be 'solid' or be screwed on with the strength of ten men.

NB from a dirt perspective, if you have only one dustcap, best to fit it to the rear wheel; the front valve stays a lot cleaner.

cheers
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mercalia
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Re: Reasons for different valve standards / advantages??

Postby mercalia » 1 Aug 2020, 11:03am

Brucey wrote:
mercalia wrote: with Presta I have found the unscrewed head can interfer with pumping too much and it wont inflate, or even deflates the tyre when you insert the pump, have to unscrew just a certain amount or it wont. tedious.


don't use a hand pump with a screw-on presta connector. Buy a decent pump, learn how to use it correctly (you don't need to push it on that far.... :roll: ) and you won't have 'problems' with presta.

Never any problems with Schrader. And the caps are better more solid. As for removing the insert I havent done it often but I have some times tightened one up - the tool is hardly rocket science -


no tool is 'rocket science' but this is scant consolation when you don't have one by the side of the road when you need it. FWIW the dustcaps with the tool built in are at best, suitable for tightening a loose insert (*) and then not always. They won't reliably remove inserts which are properly tight.

(*) which is more common than you might expect. I've seen whole batches of inner tubes with loose/leaky inserts in Schrader valves. They all had to be tightened, every single one and a dustcap with the tool on wouldn't do the job.

BTW dustcaps for presta are exactly that; merely to keep dust out; they are (unlike Schrader) not intended to provide a means of secondary air retention. They don't need to be 'solid' or be screwed on with the strength of ten men.

NB from a dirt perspective, if you have only one dustcap, best to fit it to the rear wheel; the front valve stays a lot cleaner.

cheers



you will presumable approve of these metal dust caps that have a seal at the end?
https://www.ebay.co.uk/itm/4-Top-Quality-Schrader-Metal-Dust-Caps-with-Valve-Remover-Tool-for-Cars-Bike-Van/232565429670?hash=item3625fad5a6:g:N1IAAOSwnI9cfOsi

4 for £2

Brucey
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Re: Reasons for different valve standards / advantages??

Postby Brucey » 1 Aug 2020, 11:25am

those dustcaps are better than nothing but the fitting is brass and simply isn't strong enough to tackle an obstinate valve core, either loosening or tightening. A 50-50 shot when tightening a leaky core...?

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NATURAL ANKLING
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Re: Reasons for different valve standards / advantages??

Postby NATURAL ANKLING » 1 Aug 2020, 11:26am

Hi,
The heading might as well have said just "why did we ever have disc brakes " :P
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