schrader valves - pressure limit?

People often say presta valves are better for high pressure and claim it is harder to get higher
pressures ( >4.0 bar) into schrader valves (the car type ones, hope I got that right).

Yet I regularly get 6.5 bar into 26x1.5" tubes on an MTB with Schwalbe Marathons; using a cheap
H*lfords track-pump.

And in my mis-spent youth of exploring disused warehouses and their contents, I have seen many an
(old) fire extinguisher which uses a schrader valve for filling; and is usually charged to *16* bar.

Are *all* schrader valves then really a no-no for high pressures, or is it just that there are some
bad quality ones being sold on cheap inner tubes?

Alex

 

Mr [email protected] (2.3 zulu-alpha) [comms room 2] wrote:
> People often say presta valves are better for high pressure and claim it is harder to get higher
> pressures ( >4.0 bar) into schrader valves (the car type ones, hope I got that right).
>
> Yet I regularly get 6.5 bar into 26x1.5" tubes on an MTB with Schwalbe Marathons; using a cheap
> H*lfords track-pump.
>
> And in my mis-spent youth of exploring disused warehouses and their contents, I have seen many
> an (old) fire extinguisher which uses a schrader valve for filling; and is usually charged to
> *16* bar.
>
> Are *all* schrader valves then really a no-no for high pressures, or is it just that there are
> some bad quality ones being sold on cheap inner tubes?

I'm not sure about a limit for schraders (I also remember blowing them up rock hard with garage
compressors in my yoof!) but one reason they're normally not recommended for HP is because more
force is required to pump by hand to overcome valve resistance. Also the better narrow road tubes
just tend to come in presta versions only.

~PB

 

Mr [email protected] wondered:
> Are *all* schrader valves then really a no-no for high pressures, or is it just that there are
> some bad quality ones being sold on cheap inner tubes?

I used to use schraeder valves and found them no more difficult to pump 100psi into than presta
valves. Presta valves hold the pressure better, though. With presta valves I don't need to top up my
tyres as often as I did with schraeder valves.

--
Danny Colyer (remove safety to reply) ( http://www.juggler.net/danny ) Recumbent cycle page:
http://www.speedy5.freeserve.co.uk/recumbents/ "He who dares not offend cannot be honest." -
Thomas Paine

 

Have a look at air shocks and the pumps to go with them. They use schraeder adaptors and are
normally pumped upto around 200-250psi using a pump with a small piston area to achieve the high
pressure. The general reason that schrader valves are hard to pump above 4 bar is because ordinary
pumps aren't designed to go that high.

 

Jimsnot wrote:
> Have a look at air shocks and the pumps to go with them. They use schraeder adaptors and are
> normally pumped upto around 200-250psi using a pump with a small piston area to achieve the high
> pressure. The general reason that schrader valves are hard to pump above 4 bar is because ordinary
> pumps aren't designed to go that high.

The fact remains that schraeder's are harder to pump to the same pressure with the same pump
than prestas.

~PB

 

"Pete Biggs" <pLime{remove_fruit}@biggs.tc> wrote in message
news:[email protected]...

> The fact remains that schraeder's are harder to pump to the same pressure with the same pump than
> prestas.

Do HGV's have schraeders? They must need a pretty high psi to cope with 44 tonnes even if it's
spread over 16 wheels or so!

 

"Adrian Boliston" <[email protected]> wrote in message
news:[email protected]...
> "Pete Biggs" <pLime{remove_fruit}@biggs.tc> wrote in message
> news:[email protected]...
>
> > The fact remains that schraeder's are harder to pump to the same
pressure
> > with the same pump than prestas.
>
> Do HGV's have schraeders? They must need a pretty high psi to cope with
44
> tonnes even if it's spread over 16 wheels or so!
>
>

Try that with a hand pump ...

 

On Tue, 6 May 2003 20:01:25 +0100, "Mr [email protected] \(2.3 zulu-alpha\) [comms room 2]"
<[email protected]> wrote:

>People often say presta valves are better for high pressure and claim it is harder to get higher
>pressures ( >4.0 bar) into schrader valves (the car type ones, hope I got that right).
>
>Yet I regularly get 6.5 bar into 26x1.5" tubes on an MTB with Schwalbe Marathons; using a cheap
>H*lfords track-pump.
>
>And in my mis-spent youth of exploring disused warehouses and their contents, I have seen many
>an (old) fire extinguisher which uses a schrader valve for filling; and is usually charged to
>*16* bar.
>
>Are *all* schrader valves then really a no-no for high pressures, or is it just that there are some
>bad quality ones being sold on cheap inner tubes?
>
>Alex
>
>

I've used metal faced Schraders on lab equipment which held in 700psi quite successfully. However I
would imagine that lover pressure ones found on cycles probably use rubber sealing faces.
>

--
79.84% of all statistics are made up on the spot. The other 42% are made up later on. In Warwick -
looking at flat fields and that includes the castle.

 

Adrian Boliston wrote:

>> The fact remains that schraeder's are harder to pump to the same pressure with the same pump than
>> prestas.
>
> Do HGV's have schraeders? They must need a pretty high psi to cope with 44 tonnes even if it's
> spread over 16 wheels or so!

1. HGV's use lower pressure tyres than road bikes
2. They don't use hand pumps so it doesn't matter

Note. By "harder to pump", I mean it takes more force to inflate, not that high pressures can't
be reached.

~PB

 

On Tue, 6 May 2003 23:52:02 +0100, Adrian Boliston <[email protected]> wrote:
> "Pete Biggs" <pLime{remove_fruit}@biggs.tc> wrote in message
> news:[email protected]...
>
>> The fact remains that schraeder's are harder to pump to the same pressure with the same pump than
>> prestas.
>
> Do HGV's have schraeders? They must need a pretty high psi to cope with 44 tonnes even if it's
> spread over 16 wheels or so!
>
Really?

Assuming the contact patch per tyre is 15 inches wide and 15 inches long (wild guesses but I don't
think they can be that far out) then 16 wheels gives a total contact patch of 3600 square inches.

44 tonnes is about 100000 lbs so contact pressure is about 30psi

I can't think of any reason why the tyre pressure should be higher than the contact pressure (stiff
sidewalls allow it to be lower e.g. run flat tyres).

Regards,

Tim.

--
God said, "div D = rho, div B = 0, curl E = - @B/@t, curl H = J + @D/@t," and there was light.

http://tjw.hn.org/ http://www.locofungus.btinternet.co.uk/

 

"Adrian Boliston" <[email protected]> wrote in message
news:[email protected]...

> Do HGV's have schraeders? They must need a pretty high psi to cope with
44
> tonnes even if it's spread over 16 wheels or so!

(and to pete and tim too)

Seen on the side of a tesco petrol lorry above the tyres - "150psi max".

cheers, clive

 

Alex wrote:

> Are *all* schrader valves then really a no-no for high pressures, or is it just that there are
> some bad quality ones being sold on cheap inner tubes?

I should imagine the latter. Trucks routinely run tyres at similar pressures to bicycles, and *they*
use Schraeder. You wouldn't want to pump up a big tyre like that by hand, though. A friend was
obliged to put the spare on his mother's Fiesta once, which he found to be flat. Salvation was at
hand in the form of a track pump, but even getting up to 25 or 30 psi was, apparently, a
considerable effort.

ttp://legslarry.crosswinds.net/
===========================================================
Editor - British Human Power Club Newsletter
http://www.bhpc.org.uk/
===========================================================

 

On Wed, 7 May 2003 01:39:15 +0100, "Pete Biggs" <pLime{remove_fruit}@biggs.tc> wrote:

>1. HGV's use lower pressure tyres than road bikes

I used to stick 90psi into ours. Don't know what roadies are pumping their bikes too these days (I'm
a fat-tuber)

 

Being the helpful friendly guy that I am, I have assist one young mother with a roadside flat. She
wasn't carrying a pump and I thought would be a good time to dust off the hardly ever used Zefal
I've got clipped onto my frame. She was driving a Ford Serria and even with the thing up on the jack
(her spare was flat also), it took both of us 45 minutes to get the tyre to a decent enough pressure
for her to drive to Kwik Fit.

Moral of this story really goes to car drivers. Carry a pump for your car.

I'm not sure about the psi ratings, pumping rating, etc but I do know its hard work to pump up a
tyre if you ain't got the right pump. Where I work we frequently get HGVs that routinly use the yard
pump to top up their tyres and I know that it takes them at least 5 minutes a tyre. When you have 16
you just pray you don't need to do all of them.

Gadget

 

"Pete Biggs" <pLime{remove_fruit}@biggs.tc> wrote in message
news:<[email protected]>...
> Adrian Boliston wrote:
>
> >> The fact remains that schraeder's are harder to pump to the same pressure with the same pump
> >> than prestas.
> >
> > Do HGV's have schraeders? They must need a pretty high psi to cope with 44 tonnes even if it's
> > spread over 16 wheels or so!
>
> 1. HGV's use lower pressure tyres than road bikes

About the same, judging by this: http://www.toyo.co.uk/pages/pressure.html

BugBear

 

"Tim Woodall" <[email protected]> wrote in message
news:[email protected]...

> Assuming the contact patch per tyre is 15 inches wide and 15 inches long....

Surely a 15" *long* footprint would require a huge deformation of the tyre!

 

"Dave Larrington" <[email protected]> wrote in message
news:[email protected]...
> Alex wrote:
>
> > Are *all* schrader valves then really a no-no for high pressures, or is it just that there are
> > some bad quality ones being sold on cheap inner tubes?
>
> I should imagine the latter. Trucks routinely run tyres at similar pressures to bicycles, and
> *they* use Schraeder. You wouldn't want to
pump
> up a big tyre like that by hand, though. A friend was obliged to put the spare on his mother's
> Fiesta once, which he found to be flat. Salvation was at hand in the form of a track pump, but
> even getting up to 25 or 30
psi
> was, apparently, a considerable effort.
>

I had a slow puncture on my ex-car and had to park at the airport for a wekk. Took my track pump,
one thing that was noticeable was the rubber pipe got really really hot. Glad I didn't melt it.

 

On Wed, 7 May 2003 12:22:52 +0100, Adrian Boliston <[email protected]> wrote:
> "Tim Woodall" <[email protected]> wrote in message
> news:[email protected]...
>
>> Assuming the contact patch per tyre is 15 inches wide and 15 inches long....
>
> Surely a 15" *long* footprint would require a huge deformation of the tyre!
>
Yes, probably it would. I was getting confused between eye level on the windcheetah and eye level in
a car and thinking that truck tyres were about four feet in diameter.

Also, someone has posted http://www.toyo.co.uk/pages/pressure.html which seems to say that the tyres
are about 12 inches wide so I have probably overestimated the contact patch by about 3-4 times which
would tally with the 90-120psi that this page suggests.

Oh, well. The theory was good anyway ;-)

Regards,

Tim.

--
God said, "div D = rho, div B = 0, curl E = - @B/@t, curl H = J + @D/@t," and there was light.

http://tjw.hn.org/ http://www.locofungus.btinternet.co.uk/

 

Clive George wrote:

>> Do HGV's have schraeders? They must need a pretty high psi to cope with 44 tonnes even if it's
>> spread over 16 wheels or so!
>
> (and to pete and tim too)
>
> Seen on the side of a tesco petrol lorry above the tyres - "150psi max".

I stand corrected. Thanks for checking. So max pressure a little higher than common racing bike
tyres. Still, doesn't change the argument - which is about how easy they are to inflate using a
normal bike pump.

~PB

 

On Wed, 7 May 2003 10:29:36 +0100, "Dave Larrington" <[email protected]> wrote:

>Trucks routinely run tyres at similar pressures to bicycles, and *they* use Schraeder.

If you consider the volume of air in a truck tyre, the amount which makes the difference between
100psi and 70psi on a bike tyre (about a week's worth with a decent Schraeder tube IME) would make a
difference of about 0,0000001psi [1]

[1] Yes, you're quite right, I did make that up

Guy
===
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