Tyre pressure relief valves
Discussion
thunderbelmont said:
You need OFN (Oxygen Free Nitrogen)(used by Aircon engineers to check for leaks in systems)
Because it's pretty well pure, it's more stable as tyre temp increases, this tyre pressures remain much more constant. It won't be totally stable as there will be impurities once in the tyre.
My track day car has Nitrogen in the tyres, still has temp rises, I am guessing this is because it is not 100 percent pure, must still have some oxygen in them.Because it's pretty well pure, it's more stable as tyre temp increases, this tyre pressures remain much more constant. It won't be totally stable as there will be impurities once in the tyre.
I suppose unless you have a system that can suck all the old air out you will still have issues.
So, no thoughts on these valves then ? and thanks for the replies so far.
Presuming you mean "pressure" rises...
That's always going to happen according to Gay-Lussac's gas law http://en.wikipedia.org/wiki/Gas_laws
What you don't want to happen is when there is moisture present, the pressure rise is not linear with temp.
No idea on the valves in question though. Just feels a bit nasty, drilling more holes in the wheels and having a way for the gas to escape.
Bert
That's always going to happen according to Gay-Lussac's gas law http://en.wikipedia.org/wiki/Gas_laws
What you don't want to happen is when there is moisture present, the pressure rise is not linear with temp.
No idea on the valves in question though. Just feels a bit nasty, drilling more holes in the wheels and having a way for the gas to escape.
Bert
jeff666 said:
thunderbelmont said:
You need OFN (Oxygen Free Nitrogen)(used by Aircon engineers to check for leaks in systems)
Because it's pretty well pure, it's more stable as tyre temp increases, this tyre pressures remain much more constant. It won't be totally stable as there will be impurities once in the tyre.
My track day car has Nitrogen in the tyres, still has temp rises, I am guessing this is because it is not 100 percent pure, must still have some oxygen in them.Because it's pretty well pure, it's more stable as tyre temp increases, this tyre pressures remain much more constant. It won't be totally stable as there will be impurities once in the tyre.
I suppose unless you have a system that can suck all the old air out you will still have issues.
So, no thoughts on these valves then ? and thanks for the replies so far.
@ Bert, I don't think you drill any holes in the wheels, they are a replacement type valve that releases air when the desired pressure is reached, (I think). I have only seen them for sale in the USA .
Interesting to hear that the moisture in the air causes the pressures to rise, I am guessing the Nitrogen is much more stable ?
Jeff.
Interesting to hear that the moisture in the air causes the pressures to rise, I am guessing the Nitrogen is much more stable ?
Jeff.
jeff666 said:
@ Bert, I don't think you drill any holes in the wheels, they are a replacement type valve that releases air when the desired pressure is reached, (I think). I have only seen them for sale in the USA .
Interesting to hear that the moisture in the air causes the pressures to rise, I am guessing the Nitrogen is much more stable ?
Jeff.
At the risk of repeating myself Interesting to hear that the moisture in the air causes the pressures to rise, I am guessing the Nitrogen is much more stable ?
Jeff.
The pressure rises with heat. That's physics. If you have water present, you get much more pressure rise and it's not linear.
If you look up the valves they are separate and require separate holes.
BertBert said:
At the risk of repeating myself
The pressure rises with heat. That's physics. If you have water present, you get much more pressure rise and it's not linear.
If you look up the valves they are separate and require separate holes.
No need for the rollies, I have only read one review on them, no mention of drilling extra holes, not much info on them at all, hence the question posted on here.The pressure rises with heat. That's physics. If you have water present, you get much more pressure rise and it's not linear.
If you look up the valves they are separate and require separate holes.
Thanks for taking the time to reply anyway.
jeff666 said:
BertBert said:
At the risk of repeating myself
The pressure rises with heat. That's physics. If you have water present, you get much more pressure rise and it's not linear.
If you look up the valves they are separate and require separate holes.
No need for the rollies, I have only read one review on them, no mention of drilling extra holes, not much info on them at all, hence the question posted on here.The pressure rises with heat. That's physics. If you have water present, you get much more pressure rise and it's not linear.
If you look up the valves they are separate and require separate holes.
Thanks for taking the time to reply anyway.
BertBert said:
At the risk of repeating myself
The pressure rises with heat. That's physics.
Yes but it's pV = nRT where T is the temperature in kelvins. I think over the operating temperature of a tyre the pressure increase of an ideal gas would be negligible, particularly considering that the tyre is flexible and hence the volume can change.The pressure rises with heat. That's physics.
BertBert said:
At the risk of repeating myself
The pressure rises with heat. That's physics. If you have water present, you get much more pressure rise and it's not linear.
If you look up the valves they are separate and require separate holes.
This is where the myth comes in, the physics theory tells us the moisture content makes very little difference to the pressure rise. Water is only a few percent of our air for a start. The thermal conductivity of water vapour is actually lower than air! Another one of the myths. The one and only possible reason for drying the air is to get to a position where highly accurate and repeatable forecasts can be made on the tyres pressure whereas with atmospheric air one will likely not know how much water vapour is in it and hence can't make such highly accurate predictions. The pressure rises with heat. That's physics. If you have water present, you get much more pressure rise and it's not linear.
If you look up the valves they are separate and require separate holes.
Like many things in motor sport though this in the realms of 0.01s stuff that obsesses the F1 teams and should be considered a bit silly to even think about for club racing where the consideration of whether or not one took a dump in the morning and the effect it has on weight will be more of an impact. Worrying about moist air for most guys using pressure gauges that probably aren't even accurate to less than 1 psi is just plain silly.
How many guys on here calculate what their starting ideal tyre pressure for each tyre should be for each track in the UK and for every type of atmospheric condition to tenths of a psi? Nope thought.
Edited by NJH on Monday 21st April 14:11
It's quite an interesting topic and probably of more interest to those running slicks. I thought that it really didn't matter *all* that much, but we focussed on tyre pressures a lot last season and found it made a huge difference. It's actually quite hard to get right and a lot of Friday testing was about seeing how the tyres behaved with the circuit and the conditions (and then hoping that race day would be the same).
Bert
Bert
I was asking for a club racer, (Team Trophy) so a 60 min race, when they come in for the mandatory pit stop (2 mins) we check the pressures and have to reduce them, both guys say the car felt better after the stop.
We start around 24psi cold, and they can be as high as 34 hot, both cars are on ordinary air, not Nitrogen, they are running the Khumos v70's from memory.
Just hoped that some body may have had some experience with these valves, the only review that I found on them rated them highly.
Again, thanks for the replies, much appreciated.
Jeff.
We start around 24psi cold, and they can be as high as 34 hot, both cars are on ordinary air, not Nitrogen, they are running the Khumos v70's from memory.
Just hoped that some body may have had some experience with these valves, the only review that I found on them rated them highly.
Again, thanks for the replies, much appreciated.
Jeff.
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