The work truck rears, yes. (I did note that the NTSB test tire was LT) Fronts are supposed to be but unless am fully loaded I'll generally run them about 50 instead.
For a typical passenger car tire at 30-35 psi would be less, yes, but not in the summary. I didn't read the full report in absolute total depth; whether there were additional measurements reported in the body of the report I dunno; may be.
I was somewhat surprised their measurements showed as much as they did; it seems like would be more noticeable than is routinely altho I guess I pretty-much do ignore a pound +/- either way as that's not as much as routine temperature swings cause.
No, it has pretty high humidity, which is why you need moisture traps to prevent water from getting into the paint when you use a spray gun, or to prevent water from ruining your air tools.
That is the water that came out of the air. The air itself is drier because it gave up that water. Compressed air is simply not as capable of holding water vapor so it condenses out. It is up to you to capture the liquid and get rid of it tho. Most still ends up in the tank.
When I see something that outrageous, I just tell them that and leave. I wouldn't buy a car or anything from shysters like that, plenty of other places.
Like a fellow at work did about 15 years ago. He was going to buy a new car. It had on it a certain brand of tires. His wife had a fobia about that brand as her sister was killed in a car that had that brand and a blowout caused the accident.
He asked to change the wheels (same kind of rims) with another on the lot that had a differnt brand of tires. They wanted about $ 400 to do that as they said the tires were more exensive. He told them that the whole lot of 4 tires would not cost that much if bought new, so he walked out. He told me he would have went as much as $ 100, but not get ripped off for $ 400.
The most readable and lucid description I've yet to find...
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Altho the permeability is about 3:1 O:N, the partial pressures which are the driving force are lower for N2 as the air on the outside is 79% N instead of 21% for O. So the ratio there counteracts the permeability ratio and one ends up with the observable result of only about a 25-35% difference in practice.
My experience has been converse to that -- dealers/new cars tend to be low pressure as gives perception of smoother/softer ride.
Depends on dealer prep. Many imported cars are shipped with 60 psi as they sit on a boat and then in a port lot for weeks. Dealer is supposed to lower the pressure to the required number.
Unless there's a dryer in front, it's still essentially saturated; just at a different saturation point being compressed. If the compressor is running, temperature is higher which counteracts some of the pressure-induced loss...if the compressor cuts off and the compressed tank air cools, more will condense out in the tank.
An example calculation from EngineeringToolbox web site illustrates--
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Example - Water Extracted from an Air Compressor
Free air enters a compressor at atmospheric conditions 20oC and 70% humidity ratio. The air leaves saturated at gauge pressure 8 bar and 40oC.
Based on the diagram and table above the water content in saturated air entering the compressor can be estimated to be approximately 1.8 10-2 kg per m3 free air (0.018 kgwater/m3air).
The amount of water with 70% saturation can be calculated as
(0.018 kgwater/m3air) (70%) / (100%)
= 0.0126 kgwater/m3air
The water content in the 100% saturated air leaving the compressor can be estimated from above to be approximately 0.62 10-2 kg per m3 free air (0.0062 kgwater/m3air).
The water extracted in the compressor can be calculated as
(0.0126 kgwater/m3air) - (0.0062 kgwater/m3air)
= 0.0064 kgwater/m3air
So, while the compressor took out some, it was only about half the actual water going in; the other half is still in there. If drop the tank temp back to 20C then then the 0.0062 --> ~0.002 at 8 bar and indeed, then 0.0106 kgwater/m3air would been removed; about 85% instead of just over 50%.
But, it'll still be saturated or nearly so so if blow out an open air hose it'll have noticeable condensation from the isentropic expansion cooling effect.
That's all I've bought for the last 20 years. When I asked the dealer why pressures were higher than recommended he said it was for their sitting in lots for a long time. I guess he also included shipping time.
If the tank and lines are properly drained 150PSI air at 70F will translate to a relative humidity of about 10% at 70F and 35 psi.
If the air comes from a tankless inflator (the typical "service" inflator at the gas station - or even your 12 vokt compressor or your bicycle pump) the humidity is whatever the atmospheric humidity is in absolute terms (not relative) and the moisture WILL condense out in the tire under pressure.
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