We purchased new tires for my wife's pick-up truck a few of days ago and, as an unexpected bonus for purchasing 4 Michelin tires from Costco, we were given a "3-in-1 Power Station", made in China for a Greenville, SC company named Southern Equipment. (Their normal price in the store for this device is $60.)
The device contains a maintenance-free lead-acid battery and one recharges it from a household circuit. No battery capacity is listed but it uses "Amps" throughout its description of the device's capabilities. Not enough information is given for me to calculate the capacity, either. If I ever recall where I set down the instruction booklet, it might tell me more. Among the gadgets in this thing is an air compressor. The pressure guage has a dual scale, with "lb/in2" (not "psi") on the outer scale and "kpaX100" (not "kPaX100")on the inner scale. The end of the inner scale is also labeled as "kg/cm2" and "bar". Of course the 2s in the preceding are superscripts. What I really wonder about, though, is the range of the scale, which is commensurate with the stated output pressure of the compressor. The scale "red-lines" at 1400 kPa and has a maximum scale mark at 2100 kPa. So normal automobile tire pressures are barely more than 10 % of the full scale reading. Of course, the pressure reading is taken at the discharge of the compressor and at the input end of the hose, so there will be some pressure drop through the hose and tire-stem fitting. What on Earth would require such large pressures? Tires for semi-trailers and their tractors? Since the product of pressure and volume is an energy quantity (Pa.m3=J), then pressure times flow rate represents power (Pa.m3/s=W) I would think it better to lower the pressure and to increase the flow rate. But that might require a larger space in the device's case for the compressor. This is quite similar to the pressure guage on the air compressor I purchased a year or two ago, which plugs into the vehicle's cigarette lighter. That also was made in China, perhaps for the same SC company. Jim -- James R. Frysinger University/College of Charleston 10 Captiva Row Dept. of Physics and Astronomy Charleston, SC 29407 66 George Street 843.225.0805 Charleston, SC 29424 http://www.cofc.edu/~frysingj [EMAIL PROTECTED] Cert. Adv. Metrication Specialist 843.953.7644
