How to check tire pressure with a valve like this ?

Usjes

Hi,

I bought a foldable bike and it got a puncture on the way home from the shop, so to minimize the chances of getting another I wanted to pump it up as high as the tires allowed (rated 40->65psi, so I would aim for 65psi). When I went to re-inflate the tire though I found the valve on the tube was of a type I have never seen before, see the attached photos which show the valve and how it disassembles. I use a track pump with a pressure guage and with all my other bikes I can pump to whatever pressure I like and when I stop pumping the pressure guage will remain where it is indefinitely (until I detach the pump from the valve). So there is no trouble figuring out what pressure the tyre is currently at. This new valve behaves differently though, on the downstroke of the pump handle the needle on the guage will jerk up as usual but after the plunger has reached the bottom of the pump I will then hear a secondary hiss of air and the needle on the pressure guage will fall back to 0psi. It is like the initial pump stroke pumps the air into some sort of ante-chamber in the valve and then separately it leaks into the tube proper and the pressure falls back to zero so I can never get a clean static reading of the current tyre pressure. Has anyone seen valves like this before ? How do you determine the current tyre pressure with a tube like this ?

Thanks,

Usjes.

StevieGriff

It's a woods/dunlop valve, most pumps for presta fittings will do the job. Could be reading your post wrong but are you taking out the valve core while you are trying to pump the tube?

easygoing39

Sounds like youre doing something wrong to me.When I pump up a tube with a Dunlop valve I just use the Presta side of my pumphead,pump till I get to the required pressure and then I remove the pumphead.Job done,no air lost.As Stevie above asks,are you taking the valve apart?

Lumen

http://www.schwalbetires.com/tech_info/valve

"With traditional Dunlop valves, it is impossible to check the inflation pressure."

So you're probably not doing it wrong.

I would check the pressure by sitting on the bike and observing the drop (squidge) of the tyre on the ground. When my tires are pumped to a nice pressure, leaning forward over the bars causes noticable squidge, and leaning back a bit makes it disappear completely.

Usjes

Lumen wrote: »

http://www.schwalbetires.com/tech_info/valve

"With traditional Dunlop valves, it is impossible to check the inflation pressure."

Yes, I'm sure this is it. Also from that link:
'The traditional bicycle valve or Dunlop valve is still the most common worldwide'
This is surprising to me, I've been cycling for 25years and never come across one before. As it's a foldable bike the wheels are 20 inch, I wonder do all 20 inch tubes use the Dunlop valve or would I be able to get replacements with presta or schrader valve. Not being able to check the pressure is really annoying.

Also, does anyone know why the pressure ratings are so much lower on 'fat' tyres vs. road bike tyres? On my road bike I always keep the pressure near 120psi and do believe it really does lead to far fewer punctures.
Or, to put it another way, what is the risk if I pump these 40->65 psi tyres up to like 80 psi ?

Thanks,

Usjes

Alek

This is surprising to me, I've been cycling for 25years and never come across one before.

I guess this statement includes countries like China and India... From my experience, back in the 80' there were only Dunlop valves in Poland in example...

Lumen

Usjes wrote: »

I wonder do all 20 inch tubes use the Dunlop valves

No.

Usjes wrote: »

would I be able to get replacements with presta or schrader valve.

Yes.

Usjes wrote: »

Also, does anyone know why the pressure ratings are so much lower on 'fat' tyres vs. road bike tyres?

Think about what pressure means - force spread over an area. The force is the weight of you and your bike. The area is of the contact patch with the road. If you run a low air pressure, the tyre will drop until the contact patch is big enough to support your weight. If you run a higher pressure, the tyre will rise up to make the contact patch smaller. Wider tyres have a wider contact patch, so do not require the same pressure to avoid a saggy tyre and keep the sidewall the right shape.

Usjes wrote: »

what is the risk if I pump these 40->65 psi tyres up to like 80 psi ?

If they are not rated for that pressure they may fail, or your wheel might collapse.

You only need enough pressure to keep a nice sidewall shape and correct sized contact patch.

Al Wright

When those valves were in widespread use here (pre- Kevlar/Aramid puncture resistance days), instead of recommended tyre pressures on the tyre sidewall there was the statement 'Inflate Hard'.
A few years ago, when using a Presta pump with gauge on such a valve I estimated that the pressure differential needed to drive air through one such valve was 4 psi, but on the other wheel it was nearer to 10 psi.

cdaly_

Usjes wrote: »

Not being able to check the pressure is really annoying.

Al Wright wrote: »

A few years ago, when using a Presta pump with gauge on such a valve I estimated that the pressure differential needed to drive air through one such valve was 4 psi, but on the other wheel it was nearer to 10 psi.

Using the above, it should be possible to 'check' the pressure beyond a Dunlop valve.

1. Fit pump
2. Push down with one stroke so that some air goes into tyre
3. The gauge will read the tyre pressure plus the differential pressure

tomasrojo

Usjes wrote: »

This is surprising to me, I've been cycling for 25years and never come across one before. As it's a foldable bike the wheels are 20 inch, I wonder do all 20 inch tubes use the Dunlop valve or would I be able to get replacements with presta or schrader valve.

They're not always used with smaller wheels, no, but funnily enough, my only set of them was in my first set of wheels for my Bike-Hod trailer, which has 12" wheels.

The little rubber tube that used to be in pucture repair kits was for Dunlop/Woods valves. They definitely used to be common here.