Since my first motorbike, over 35 years ago, I've changed the plastic tyre valve caps for metal ones, as they act as a secondary seal should the valve core leak.
I've never had any problems, and so in the last couple of years, have left the extension type caps on the Golf, as they make checking pressures easier (even if I still have to take them off to pump the tyres).
However, when I went to check the pressures on my daughter's car this evening, as I undid the metal cap, air came hissing out. Eventually I found one of those devices for screwing the valve core back in and was able to do up the core tightly again.
Point is, that tyre had been on the front for about a year and there was no sign of trouble a fortnight ago when I last checked the pressures (always do it when she returns for a flying visit); if I'd left a plastic cap on it, at best it would have caused an inconvenient flat, at worst...
I'll be changing the extention caps for metal ones when I can get to the shops again...
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I always thought the extension type caps that I have seen on VW's to be a very good idea and should be used as the standard.
I would not have thought the problem you encountered would be connected to the type of cap used.
(BTW - I had my metal caps nicked so only use the palstic ones now).
Now and again the valve can come loose and it is worth just checking for tightness every 6 months or so.
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I will never fit metal caps again, people just come along and nick them.
Plastic ones only from now on.
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Plastic ones don't get pinched, simple.
Alloy/Metal look nice but the 'blaggers' in the street like the shiny ones - less damage to my car if they aren't fitted. Probably end up on BMX and MTB's anyway.
I've been really picky keeping my plastic valve caps since I got the car - all the same (for once) !
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if metal are better but attract magpies ,just paint them matt black
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Yup; had smart metal ones on my Vectra 2.5 V6 GSi Estate, and scrotes nicked them in short order.
On fitting the replacements, I nipped them up tight with a spanner, and kept the spanner in the toolkit for use when tyre pressure checking / inflating.
In due course the day came, so out came the spanner and I sheared the entire valve stem in two.
Pshhhhhhhhhhhhhhhhh.
One flat tyre within the space of ten seconds!
Without wishing to tempt fate, I have however had very nice chromed metal valve caps on my V70, together with chrome valve stems, for the past 18 months and nobody has shown the slightest "interest" in them. The fact that my seriously tuned turocharged Swedish (okay, Belgian) family wagon would totally destroy the 200 bhp Vectra at any speed obviously counts for less than an overt body kitted and bespoilered machine when it comes to looking for things to nick.
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> Oldman wrote: if metal are better but attract magpies ,just paint them matt black
Now there's someone who thinks outside the box! Good comment :o)
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Good grief! Are you saying people are stealing the valve caps off cars now?
I lost a spare tyre from under a Citroen BX once
but a metal valve cover! Unbelievable!
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In the 1960s I fitted aircraft metal valve caps ~ mainly because, being yellow, they were hignly visible so they appealed to the flamboyant nature I had at the time, and (important at the time because I was not very well off) I could get them for nothing. I found that the extra mass caused the valve stems to bend radially outwards until the cap touched the wheel an damaged the paint. Ever since I've stuck to plastic caps. Nowadays these incorporate a seal anyway.
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L\'escargot.
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>>would not have thought the problem you encountered would be connected to the type of cap used.>>
Good metal ones with a seal will retain the air pressure if the valve leaks / fails, plastic ones wont.
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A couple of years ago it was the primary-school children in this locality who were the thieves of metal valve-caps. The local accessories shop knew all about it, always running out of stock.
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I don't see why metal ones should be any more air-tight than plastic. They both have a rubber washer.
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I don't see why metal ones should be any more air-tight than plastic. They both have a rubber washer.
The normal plastic ones are dust caps, no more, they are not designed to retain 30 to 40 Psi.
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" I found that the extra mass caused the valve stems to bend radially outwards until the cap touched the wheel an damaged the paint."
Good grief!
What sort of speed do you need to attain to do that?
And why didn't an aircraft wheel do the same?
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" I found that the extra mass caused the valve stems to bend radially outwards until the cap touched the wheel an damaged the paint." Good grief! What sort of speed do you need to attain to do that?
Singer Chamois ~ the valve stem orientation was very close to being parallel to the axial of the wheel. The manufacturer's quoted top speed was 78 mph but this was never attainable on normal roads.
And why didn't an aircraft wheel do the same?
I have no idea what the design of the aircraft valve stem was like or what the angle relative to the axis of the wheel was. If the orientation of the valve stem was radial then there would be no forces on it trying to bend the stem, only stretching forces.
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L\'escargot.
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Don't see what all the fuss is about. Until my current car (a Golf), fitted with those plastic 'easy check' ones, I always replaced those cheap plastic dust covers with a set of plated metal valve caps but these never stayed that bright thus attracting the scrotes out there. Over a period of a few months they always became dulled and mellow thus being less noticeable - consequenly never lost any to thieves.
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The normal plastic ones are dust caps, no more, they are not designed to retain 30 to 40 Psi.
But they don't normally have to. All they might have to do is hold a smaller pressure if the valve is leaking a little. You notice this if you do the spit test and find a small bubble appearing, but stop the tyre losing pressure by screwing the cap on. Plastic caps seem just as capable, but obviously it would be much better to fix the faulty valve.
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Last time I was in England I left the car for one hour in an on-street parking space near the centre of Weymouth. All the pressure-sensing dustcaps vanished.
Now planning a visit to the UK and trying to remember to put plastic caps on for the duration.
Sad, isn't it?
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What do they do with them? Are people being offered hot valve caps by the dozen in the pub?
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"Now planning a visit to the UK"
Is this trip absolutely necessary mike, some of the bus drivers are polish now. Do you really want to risk it?
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Yes it is - I've gone 18 months without Ringwood Best Bitter and real fish and chips - and I'm down to my last bag of cheese and onion crisps...
When I lived in UK I used to catch the bus! Don't mind what they speak as long as they know where they're going...
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Yes it is - I've gone 18 months without Ringwood Best Bitter and real fish and chips - and I'm down to my last bag of cheese and onion crisps... When I lived in UK I used to catch the bus! Don't mind what they speak as long as they know where they're going...
Meet you in the Inn on the Furlong for an Old Thumper?
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Could do but I'll leave the Old Thumper to SWMBO - she's the only one who can cope with that sort of stuff!
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>> I don't see why metal ones should be any more air-tight >> than plastic. They both have a rubber washer. >> The normal plastic ones are dust caps, no more, they are not designed to retain 30 to 40 Psi.
Neither are the metal ones, the valve does that job, the caps are there to prevent dust entering the valve. Whether they are metal or plastic is just aesthetic.
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>Neither are the metal ones, the valve does that job, the caps are there to prevent dust entering the valve.
> Whether they are metal or plastic is just aesthetic
You obviously missed the OP.
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>Neither are the metal ones, the valve does that job, the caps are there to prevent dust entering the valve. > Whether they are metal or plastic is just aesthetic You obviously missed the OP.
Er no, the purpose of valve caps are as I said, to prevent dust entering the valve. Although some, metal or plastic, may hold pressure, they are definitely not designed to.
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That will teach me to tempt fate by saying that was the first problem with valves I've had in 35 years - I discovered the Golf had a tyre way down on pressure on Saturday; turned out to be a leaking valve! Twice in a fortnight/35 years...
From this I can say that the VW extension caps definately are not airtight (I've now replaced them with a set of discrete metal caps).
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Crikey ! I thought I was fussy about things, but this isn,t a subject I had ever considered. Do metal valve caps realy give a better seal ???
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Crikey ! I thought I was fussy ..........
When I used the word "crikey" on this forum it was pointed out to me that I was showing my age because "crikey" is no longer in general usage! Quaint, nevertheless! ;-)
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L\'escargot.
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Perhaps that's how DD's language filter missed it.
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I had some snazzy little BMW ones on my car (bought for me as a present). They had a miniature allen key to tighten them up to the thread to stop them getting pinched.
After a couple of months I noticed 3 were missing.
I hate the thought of some urchin helping themselves to bits from my car.
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The normal plastic ones are dust caps, no more, they are not designed to retain 30 to 40 Psi.
>>But they don't normally have to. All they might have to do is hold a smaller pressure if the valve is leaking a little. >>
It is not only how much it leaks relative to the volume of the tyre (leaking "a little") rather it is about pressure and how much it leaks relative to the volume of the cap, a 35Psi tyre leaking though the valve veeeeerrrrrrry slowly does not take long to create say 30 + Psi in the very small chamber that is the cap.
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Slow leaks aren't really the issue, metal caps offer much better resistance against a sudden failure of the valve, which would have catastrophic consequences on the road.
Having said that, I can count all of the sudden valve failures I've seen on the fingers of one thumb!
Number_Cruncher
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Slow leaks aren't really the issue, metal caps offer much better resistance against a sudden failure of the valve, which would have catastrophic consequences on the road.
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Which was my original point on the matter.
Having said that, I can count all of the sudden valve failures I've seen on the fingers of one thumb!
Likewise ;-)
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Bloke at work put nice shiny alloy valve caps on last a couple of months ago. Recently had to pay the local tyre fitters to remove the tyre and replace the valve after the nice alloy cap electrolytically corroded to the valve.
Edward
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When using the vehicle for safaries etc. Land Rover used to recommend steel valve caps. Along with a decoke set, full set of bearings and seals and so on.
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after the nice alloy cap electrolytically corroded to the valve.
In two months?
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L\'escargot.
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Sorry, maybe it was a bit longer - sleepless nights means I lose track of time. It is a Citroen C2 GT and he put the caps on before the winter gritting season started. He also regularly spends the weekend on the Norfolk coast - which probably didn't help. One cap got completely corroded on, one he managed to remove with two sets of pliers and the other two came off OK.
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>>Which was my original point on the matter.
I got the impression you were talking about slow leakage, rather than sudden valve failure.
Number_Cruncher
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>> I got the impression you were talking about slow leakage, rather than sudden valve failure.
My first post in this thread said "Good metal ones with a seal will retain the air pressure if the valve leaks / fails, plastic ones wont".
Otherwise I was countering the view expressed that caps might only have to hold a a smaller pressure if the valve is only leaking a little because, of course, pressure and volume are not interdependent.
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I was told some years ago that at vast velocities centrifugal and/or centripetal forces tend to depress the innards of the valve and let air leak out. The caps prevented it escaping.
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Crumbs - didn't expect my original posting to generate so much debate!
From Wikapedia (ref: h t t p : //en.wikipedia.org/wiki/Schrader_valve) :
"A valve cap is essential on a Schrader valve because if one is not fitted, dirt and water can enter the outside of the valve, potentially jamming it or contaminating the sealing surfaces and causing a leak. Metal valve caps usually have a small rubber insert to permit a good seal against the valve body; a cap of this kind also helps to prevent air escaping from a slightly leaking valve. However, the vast majority of Schrader valves used for tires are fitted with plastic caps which effectively serve only to keep contaminants out of the valve stem."
I've never had a metal cap half-inched - I'm talking about the simple caps, not fancy lumps of adonised alloy or plated metal.
The point I was making was that in 35 years odd, I've never had a problem with a valve (I've done 30k/year for 20 years), but this one suddenly woke up and worked itself half undone in a fortnight...
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>> >> The normal plastic ones are dust caps, no more, they are >> not designed to retain 30 to 40 Psi. >>
Good answer, I honestly never thought of that scenario.
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I hadn't realised that metal caps could help prevent air loss whereas plastic ones didn't. However, I would warn against not replacing a lost one asap!
Some years ago, on my old Sierra, I was tardy in replacing a lost plastic valve cap and after putting some air into the tyre, set off on a journey. After about 40 miles of straight road I had to negotiate a roundabout whereupon I realised that the tyre had gone flat and started to shred.
I put it down to the fact that there had been dirt in the top of the valve which I had blown into the valve seal whilst inflating the tyre. Ever since, I've kept spare valve caps to hand.
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After a couple of months I noticed 3 were missing.
So you only check your tyre pressures every three months? I am aghast.
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What about a set of these? tinyurl.com/2p7wcm
Chrome plated for maximum bling effect, rubber seal for air retention, locking screw for theft-resistance, and hexagon head in case they corrode onto the valve. What more could you ask for?
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L\'escargot.
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