Air Compressor Question-filling tires

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Old 12-30-06, 01:45 PM
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Air Compressor Question-filling tires

I have a Craftsman 1HP 3 gallon air compressor. It should be enough for my needs. It runs the nailer and stapler perfectly but its other intended use it does not-tires. Trying 2 air chucks and 2 hoses( one 1/4 and one 3/8) it will only fill tires to 25-30PSI. Why is that? I have the regulator set 90-100 but still it fills them to about 30 and then stops filling them with air. I have tried many tires and it is consistent. Physics would say that the compressor will continue to put out air until both are at roughly the same PSI. Surely, tires cannot restrict the filling by almost 100 PSI. With the compressor at 125 and the tire at 30, I cannot add any air at all.

I must be doing something wrong. Please help.

Adam
 
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Old 12-30-06, 06:40 PM
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Adam: it is a volume thing rather than pressure. True if both the tire and compressor tank were the same size, they would equalize at max pressure. But, if you take the volume of the tire and the volume of the tank, you will see the tire is much larger, and therefore unequal, pushing back the pressure into the smaller vessel until it shuts down. Physics 201.
 
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Old 12-30-06, 09:37 PM
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Chandler,I'm going to stop listening momentarily and open my mouth. How does a tire w/ 30 psi force air back into a tank w/ 100 psi????I may be wrong but if you had a tire 10' tall w/ only 30 psi in it,the 100 psi from the 3 gal tank is going to go in that tire.
John, I think you need to take a serious look at your tire gauge.Buy/borrow another gauge to check against yours.I had one that showed 32 psi in a tire after airing it up and there wasn't much tread touching the ground. Bought a new one and it showed 54 psi in the same tire.
Mike
 
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Old 12-31-06, 04:45 AM
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The volume of air in a 10' tall tire will force the pressure in a smaller vessel to increase disproportionally and shut off the compressor. Granted, the pressure will equalize, but it will take several cycles of the compressor to accomplish this.
I had the same question when filling a portable tank from a pancake compressor, and couldn't even pump up a small tractor tire, so I had it explained to me by a retired Doctor of Physics. It seemed to be a no brainer for him, but it was "duh" to me. Filling the tank from my 26 gallon compressor was no problem.
 
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Old 12-31-06, 06:50 AM
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Well, I guess it's still a "duh" to me.I wish the Dr. could explain how a gas powered compressor w/ the small twin tanks can air up a combine tire 6' tall and over 2' wide w/ no problem.
Mike
 
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Old 12-31-06, 02:40 PM
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I cannot get any air from the compressor to cycle the pump. Tire at 30 and compressor at 125-nothing moves. is there anyway to overcome this? I made it through 2 semesters of physics and learn something useful now??
 
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Old 12-31-06, 07:54 PM
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It sounds to me like you have a bad tire chuck. It may not be depressing the core in the shrader fittting or opening the self closing valve in the chuck itself.
 
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Old 01-01-07, 12:51 PM
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I was hoping for the same thing. I now own 2 hoses (1/4 and 3/8) and 3 fittings )2 standard and one dual sided truck type) to fill tires. It is a standard tire valve stem that I am working with albeit from 2 motorcycles and 2 trucks. The motorcycle tire gets to about 25 while the larger truck tire gets to 31. I have numerous tire gauges, one of which is a nice digital one. All gauges read real close to the same. All valve stems and tire chuck should be the same size-right?
 
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Old 01-01-07, 07:04 PM
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Stems and chucks are supposed to be standard but I also have trouble with the odd one.
Is it possible that your hose is connected to the output of a regulator on the compressor.

A trick that many tire shops use is to remove the stem from the shrader fitting, fill the tire to pressure and then put the shrader in while air is escaping.
You may not want to try this but it might tell you something if you do.

I'm sure the solution to your problem will be an extremely simple one.
 
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Old 01-01-07, 07:46 PM
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There's a nifty device for about $20 that has a pressure guage and air valve in the same unit. Open the valve and air flows. Let the valve close and the guage reads the tire pressure. Works like a champ.

I suspect that the pressure guage on the compressor is faulty. If the regulated output pressure is higher than the current tire pressure, air should flow. No flow, something's not reading correctly.
 
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Old 01-06-07, 04:23 PM
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Went back to Sears and asked about the compressor. Book says that the compressor will put 33 psi into a standard car tire. Salesman could not elaborate, but I assume it is what Chandler said or something close. Cannot believe that this was not even a question I thought could come up with the purchase. next question was whether a similar compressor with larger volume could do what I needed. Looking at a 4 gal 1 hp pump vs my 3 gal. Salesman said it would do better but book review showed same output with 33 psi in standard tire. I have larger tires which explains why I only got to 30 or so. This leads me to believe that it is the not the size of the tank, rather dependant on hp.?. A 5 gallon air tank (no compressor) filled the tire as needed. I guess I need to hard line the tank into the compressor and run stuff from the tank. Wierd.
 
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Old 01-06-07, 05:48 PM
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I too believe what Sears was talking about was what Chandler had said about the volume of the storage tank.
The three gallon volume of air would fill a tire of determined size to 33 psi before the compressor restarted.
If you definately have the regulator set and are getting 90 to 100 psi at the chuck you will eventually fill that tire to either 100 psi or to bursting.

Post the model of your compressor so we can look up the cfm capacity.
 
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Old 01-22-07, 08:14 PM
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I have a craftsman 1hp 3g air compressor...rated at 2.4SCFM at 90PSI
With the regulator at 125 and the tank at 125 I cannot get air into the tire anymore after about 30 psi. Tried again today on a normal car tire and it will inflate those to 40psi (which is too much) but still not put over 30 in a motorcycle tire. This proves things work, but not on large truck tires (35s) nor a bike tire.
 
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