Technical Schrader Valve Question

Had to replace a bad tire valve. Both the one that came out and the replacement had red sealing bands, as in the part no. 054051000. The accompanying chart lists "opening pressure 90 psi". Does that mean 90 psi needed in the compressor line to put air in the tire? Doesn't sound right.

https://www.schrader-pacific.com/media/pdf/Valve Core Brochure.pdf

 

I know nothing about the red bands or what they mean, but my guess is they will effectively hold pressure up to 90PSI?

 

Page 1 of link posted states...
"Valve cores are defined by their characteristics, and depending on the type selected, these characteristics vary depending on the material, the finish and the design of each valve core.

Opening Pressure: This is the typical air pressure necessary to overcome the resistance of the spring that keeps the valve closed, allowing air to pass through.

Minimum and Maximum Travel: This is the recommended distance the pin can travel without damaging the valve core. This information can be found on specific Schrader-Pacific drawings."

 

The band color must not be a standardised thing. I could push them open easily with a finger.

 

Think of the Schrader valve as a check valve. The air in the tire (in this case) is pushing against the schrader valve, and the valve will not allow any pressure to escape up to 90 PSI (or whatever the schrader valve is rated at). At any pressure above 90 PSI (or the rated pressure of said valve), all bets are off.

 

If you're talking about pressure, then comparing it to the force to open the valve, you are forgetting the important thing about pressure--it's related to area (that's why it's Pounds per Square Inch). The 90 psi air pressure required to open the valve, acts on a very small area. The Square Inches is less than .01, so it should take less than a pound of force on the spring to do the same thing.

 

That same valve, on the chart, list 250psi as 'max working pressure'.

Right, I did neglect that. However aren't the area of the valve seat inside and the head of the pin roughly the same size, give or take? The I don't understand the 1 psi vs 90 psi difference.

 

Good deal....the reference to the 90 PSI was just a reference.....I don't know shit about schrader valves, except that I have welded 1000s of them into refrigeration systems over the years, and will hold refrigerant in a high pressure system as needed, mostly.....

 

1 pound per 0.01 square inches, is equal to 100 pounds per 1 square inch.

It's really hard for lots of folks who didn't study engineering, to understand that pressure and force are NOT the same thing. Pressure is Force, applied over an area. The size of the area makes a big difference.

Sorry I'm not good at teaching this kind of stuff...

 

It really isn't rocket science. The low pressure valves are for tires you might be far more inclined to pump with a hand pump like a bicycle tire. 25/35 lbs of air pressure (not finger pressure) To open the valve is about what you could expect out of a hand pump. The 90 lb on the one with the red silicone just flat takes more air pressure in the line to open it and get air in the tire.

 

Think needle and seat on a carburetor. The smaller the hole the greater it can hold back pressure. The larger the hole the lesser it can hold back pressure.

 

Bottom line: It will work just fine.

 

Interesting fact" The Schrader valve it one of the oldest unchanged items used on today's cars. Original patent date 1893.

 

Ok, finally sunk in! Thanks!

 

Does my car get heavier if I put 5lbs more air in each tire?

 

Do the math. 5# times 4 tires, your car is 20# heavier. Easy.

 

Is that five pounds of air, or five more pounds per square inch of air pressure?

 

How many bags of air does it take to make 5 pounds?

 

What size bags?

 

What pressure is the air in the bags?

 

I'm confused.

 

If you think about it.... An air nozzle for filling tires has a nipple in the center of the fitting to open the schrader valve to allow air to pass thru it for inflation. Not sure why they have a rating for how much air pressure it takes to open it. If the tire has 30 psi in it I would think that would increase the amount of pressure to open it. Kind of confusing.

 

Mounted a truck tire one day, told my helper to air it up to 100psi, after he was done I said ok now help me flip it into the back of my pickup.......................his comment was we should have done that before he the extra 100lbs in it......................................hard to keep a straight face in this job.

 

As many bags as you need to have ~2 cubic meters of air at atmospheric pressure.

Don't some compression testers use a similar type valve as a check valve to hold the peak reading? A very low opening pressure would be important there, while it doesn't matter on tyres where you fill with a nozzle that pushes the valve open.

 

And in electric pressure is voltage..

 

And the flow rate is?

 

Current, amperes.

 

And when you put pressure and flow together you get?

 

Power, watts (or horsepower).

 

And when you touch it all together with your hands, what's it called?

Assuming you are firmly plated on the ground.