yes; that is the way most presta chucks are designed to work.
The kind that open the valve when you connect is very much the exception and normally requires that you have a screw-on adaptor of some kind; this is the only way on ensuring that the valve is at the right height to be opened and even then it isn't consistent between brands of valve; they vary slightly.
If you need to push a twinhead on so far that the valve opens when you connect, else it leaks when you pump, there is almost certainly something wrong with it; probably the seal is worn/wrong or some other part is worn and the thing needs a spacer in it so that the seal grips properly.
If you use a (normal) non-valve opening chuck, it is best to tickle the valve before you connect (it may jam in the closed position otherwise; remember only air pressure will be causing it to open), then connect (no air loss), then after one or two pump strokes air should be going into the tyre and the gauge will be reading accurately.
cheers
Dual Head presta/Shraeder adapter
Re: Dual Head presta/Shraeder adapter
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Re: Dual Head presta/Shraeder adapter
I agree with you.
I agree that it is the way things should work.
BUT the Twinhead has always - even from brand new - released air as it is connected and disconnected.
Maybe it is defective. It isn't the seals coz I've replaced them.
Looking in the shed for the item this evening so I could experiment and photograph, it seems that I have chucked it out along with other useless stuff.
I have a couple of car pumps. One cigar-lighter powered, and a double cylinder foot pump. Both, when connected to a car tyre, show the pressure as soon as I connect. This MUST mean that the Shrader valves are depressed as I connect.
This is the symptom I found with the Topeak Twinhead on Presta ............ and as it happens, on Shrader too.
I agree that it is the way things should work.
BUT the Twinhead has always - even from brand new - released air as it is connected and disconnected.
Maybe it is defective. It isn't the seals coz I've replaced them.
Looking in the shed for the item this evening so I could experiment and photograph, it seems that I have chucked it out along with other useless stuff.
I have a couple of car pumps. One cigar-lighter powered, and a double cylinder foot pump. Both, when connected to a car tyre, show the pressure as soon as I connect. This MUST mean that the Shrader valves are depressed as I connect.
This is the symptom I found with the Topeak Twinhead on Presta ............ and as it happens, on Shrader too.
Mick F. Cornwall
Re: Dual Head presta/Shraeder adapter
all Schrader connectors are meant to open the valve, because pressure alone is unlikely to open a Schrader valve insert; the springs in them need to be strong enough to withstand being centrifuged open at 150mph + ....
The twinhead connector is designed to open Schrader valves but not presta ones.
cheers
The twinhead connector is designed to open Schrader valves but not presta ones.
cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Re: Dual Head presta/Shraeder adapter
I think I've sussed it.
I've been using Schwalbe tubes for years. The Schwalbe valves are quite different to "normal" Presta valves.
Here lies the problem, I think.
Quick measurement from Schwalbe vs a old tube.
Schwalbe from tip to parallel threaded area is 13.5mm
Old from tip to parallel threaded area is 11.2mm
Hence I have to push the Twinhead over 2mm further on, and the tip gets depressed.
I've been using Schwalbe tubes for years. The Schwalbe valves are quite different to "normal" Presta valves.
Here lies the problem, I think.
Quick measurement from Schwalbe vs a old tube.
Schwalbe from tip to parallel threaded area is 13.5mm
Old from tip to parallel threaded area is 11.2mm
Hence I have to push the Twinhead over 2mm further on, and the tip gets depressed.
Mick F. Cornwall
Re: Dual Head presta/Shraeder adapter
maybe that is part of the trouble like you say....
cheers
cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Topeak twinhead variations
I have two Topeak Twinhead chucks and in light of Mick's comments I took a closer look at them. One has a yellow lever and the other has a red lever. Neither is the very latest version;
Now the thing is that these chucks are not identical;
Yellow has a barrel nut which is tightened using a pin spanner, head of 52mm width, 21mm deep Presta fitting (reducing to 19.5mm when the chuck is tightened), 10mm deep Schrader fitting, accepts flanged seal inserts.
Red has a slotted barrel nut, head of 65mm width, 26mm deep Presta fitting (25mm closed), 13mm deep Schrader fitting, does not have flanged seal inserts fitted.
Both use the same end caps, but different seals. The one with the yellow lever appears to be the more common variety, for which seal kits are readily available. The seals are the same diameter into the body but different lengths, so the seals don't interchange between the two.
The seals in the yellow head look like these;
Between the two heads the difference in the depths of the presta fittings is significant; the red head gives you the choice of trying to seal around the larger part of the valve stem (which you might want to do once the seal is worn; if you try this with a new seal you will wear it prematurely) but the yellow one will struggle to reach this far without opening the valve during connection. Obviously if the valves vary in length so will the likelihood of this happening.
Both types are really designed to seal around the narrowest part of the valve stem like most other presta connectors, i.e. without opening the valve. To ensure that air goes into the valve easily, it is always best to open a presta valve briefly i.e. unseat it, before trying to inflate the tyre. if you don't do this you may find that no air goes into the tyre even when the gauge is reading 200psi, because the valve is still jammed shut.
cheers
Now the thing is that these chucks are not identical;
Yellow has a barrel nut which is tightened using a pin spanner, head of 52mm width, 21mm deep Presta fitting (reducing to 19.5mm when the chuck is tightened), 10mm deep Schrader fitting, accepts flanged seal inserts.
Red has a slotted barrel nut, head of 65mm width, 26mm deep Presta fitting (25mm closed), 13mm deep Schrader fitting, does not have flanged seal inserts fitted.
Both use the same end caps, but different seals. The one with the yellow lever appears to be the more common variety, for which seal kits are readily available. The seals are the same diameter into the body but different lengths, so the seals don't interchange between the two.
The seals in the yellow head look like these;
Between the two heads the difference in the depths of the presta fittings is significant; the red head gives you the choice of trying to seal around the larger part of the valve stem (which you might want to do once the seal is worn; if you try this with a new seal you will wear it prematurely) but the yellow one will struggle to reach this far without opening the valve during connection. Obviously if the valves vary in length so will the likelihood of this happening.
Both types are really designed to seal around the narrowest part of the valve stem like most other presta connectors, i.e. without opening the valve. To ensure that air goes into the valve easily, it is always best to open a presta valve briefly i.e. unseat it, before trying to inflate the tyre. if you don't do this you may find that no air goes into the tyre even when the gauge is reading 200psi, because the valve is still jammed shut.
cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Re: Topeak twinhead variations
Thank you VERY MUCH for your enlightening post, and this bit in particular.Brucey wrote: .................... but the yellow one will struggle to reach this far without opening the valve during connection. Obviously if the valves vary in length so will the likelihood of this happening.
It explains everything.
Mine was a Yellow one ................ and I reckon useless even with brand new seals. I struggled with it for years expecting it was normal to be like that. It wasn't until this subject was talked about on here that I realised mine was terrible so replaced the seals. It was a bit better, but still terrible.
No doubt it would be fine for a sub-80psi bike, but the thing would blow off mine unless it was pushed (as it happens) too far on.
Mick F. Cornwall
Re: Dual Head presta/Shraeder adapter
PS.
I wonder if I bought the wrong seals?
Too late now, the whole thing was thrown away months ago.
I wonder if I bought the wrong seals?
Too late now, the whole thing was thrown away months ago.
Mick F. Cornwall
Re: Dual Head presta/Shraeder adapter
Coming to this late I know, but I have a Park track pump (PFP8), and I chose it as a lightweight alternative to my Topeak Joe Blow (yellow head) for carrying to Dr Bike events and schools. The final straw with the flimsy Park was that it pulled out a customer's Presta valve when I was trying to release the head. I never managed to figure out how that head fitted the valve properly - it was one of those that never seemed to allow air into the valve and hissed instead. Most irritating.
The Topeak is a solid thing but the heads that I have used (two so far) don't last long due to the plasticky pin inside for Schrader valves becoming crushed and useless after a few months use (I do a LOT of pumping for work). I have seen other heads that have a metal pin - does anyone know of a pump head that will work well and last? I will happily buy a couple!
Thank you
The Topeak is a solid thing but the heads that I have used (two so far) don't last long due to the plasticky pin inside for Schrader valves becoming crushed and useless after a few months use (I do a LOT of pumping for work). I have seen other heads that have a metal pin - does anyone know of a pump head that will work well and last? I will happily buy a couple!
Thank you