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Post by c64 on Sept 21, 2014 19:35:27 GMT
Today I was at a fuel station checking tire pressure.
Just before I climbed out of my car, someone else had grabbed the hose of the air pump. It's one of those modern "automatic" ones with a very long hose and a digital gauge and Preset. I couldn't belief the pressure she had dialed in and asked her if she is sure of the pressure she had picked.
"Of course", she said, "I am not stupid. I have to select more since the hose steals 0.2 bar (~3 PSI), I have tested it!
I tried to explain that the hose steals the air before the pump inflates it back to the dialed in preset so what the pump is displaying when it beeps "ready", that's what is inside the tire after disconnecting. I also said that I can see that her tires are very worn in the middle but are factory fresh on the edges but she wouldn't listen. Her husband is a trucker and knows a lot more than I do.
Now this worries me not only of her sling shooting herself into a guardrail but her husbands truck THROUGH a guardrail into oncoming traffic!
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Post by the light works on Sept 22, 2014 3:45:24 GMT
Today I was at a fuel station checking tire pressure. Just before I climbed out of my car, someone else had grabbed the hose of the air pump. It's one of those modern "automatic" ones with a very long hose and a digital gauge and Preset. I couldn't belief the pressure she had dialed in and asked her if she is sure of the pressure she had picked. "Of course", she said, "I am not stupid. I have to select more since the hose steals 0.2 bar (~3 PSI), I have tested it! I tried to explain that the hose steals the air before the pump inflates it back to the dialed in preset so what the pump is displaying when it beeps "ready", that's what is inside the tire after disconnecting. I also said that I can see that her tires are very worn in the middle but are factory fresh on the edges but she wouldn't listen. Her husband is a trucker and knows a lot more than I do. Now this worries me not only of her sling shooting herself into a guardrail but her husbands truck THROUGH a guardrail into oncoming traffic! her husband doesn't comprehend the difference between static pressure and dynamic pressure. friction loss only affects dynamic pressure. he also knows nothing about reading treadwear. now if there was a significant altitude change - by which I mean hundreds of feet considering it is air we are talking about - there would be some pressure loss.
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Post by silverdragon on Sept 22, 2014 9:19:01 GMT
Excuse to get rid of you because she doesnt want to listen.
People like that should be ignored.
However, if a pressure guage on a air pump is not correectly calibrated every now and again, it may not work right.
I carry a digital tyre gauge in my car, I NEVER trust garage tyre gauges, and mine is calibrated correct. I have found anything from ~ 3psi either way from Garage tyre gauges, and those were only the ones I could read.
But I do know from tapping a tyre how much it is to the nearest 5psi..... which is good enough to get me where I can get a better reading?... carefully though.
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Post by c64 on Sept 22, 2014 10:59:39 GMT
In Germany, the gauging office checks gas pumps and air pumps of fuel stations regularly. So if you use the air pump, the reading is as official as it can be. The "Myth" is, that people belief that the hose steals air so the preset is wrong and you get less air pressure with the long hose. I had forgotten to mention that I had heard that one pretty often. Originally, the common tool to check/inflate your tire was this: It's an air tank with a gauge and two buttons (+/-) which hangs on the air outlet of the gas stations compressor to refill. You pick it up and take it to your wheels. Convenient and worked well. But more and more of those become stolen. Then they came up with a wall mounted version which started the myth because those had to have a really long hose. You connect it to your wheel, walk back and dial in the pressure with the +/- buttons. When you connect the hose to the wheel, a lot of air rushes into the hose decreasing the tire pressure significantly. E.g. you have dialed in the correct pressure, e.g. 2.0 bar, disconnect the hose with a loud hiss and then reconnect, the gauge will read 1.8 bar or less (~3 PSI less) because the hose really steals pressure when connecting. The problem is that the loud hissing sound appears when disconnecting the hose so people think the hose will steal the air out of the tire in this moment and not when connecting it before the pressure is dialed in. So people wrongly belief they must compensate this loss by dialing in extra pressure. Some gas stations came up with an "Air Column" to reduce the length of the hose, which is much more user friendly since you don't need to pull the hose all the way around your vehicle and then coiling up the dirty hose to put it back into the wall cradle. And the more modern versions like in the picture have a preset, just dial in the pressure you need, connect the hose and wait until the thing beeps, then move to the next wheel. But there are still many people who think the hose will steal air and need to add more air to the wheel to compensate. Yesterdays encounter was at a modern "Air Column" but one with an extra long hose because they had only one of those for 4 service spots.
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Post by wvengineer on Sept 22, 2014 12:33:45 GMT
There is a gas station locally with a similar style of automatic air pump. I keep a good tire gauge in both of my cars so I always check it. For me, I can set those things to a desired pressure, but those things keep pumping air after my gauge says that it is where I want it. I trust my gauge more than I trust the pump's.
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Post by Cybermortis on Sept 22, 2014 12:45:34 GMT
Interesting.
On its own this might be a little, well, threadbare - in so far that there doesn't seem a great deal of potential testing or expansion.
However, what about 'Forecourt Fables'? As in a number of smaller car/tire/gas station myths they could look at in conjunction with this? For example the idea that 'super unleaded'/high octane gasoline will really improve performance of the average car, or what happens if you fill your diesel car with gasoline?
Ideas?
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Post by the light works on Sept 22, 2014 14:04:54 GMT
I like adding the other forecourt myths.
I see where the difference is - here, most air stations use a hose with a pressure seal in the end of the hose - the better ones have a control and gauge at the tire, while the cheaper ones just have the fitting. you press the fitting onto the valve stem to release airflow. the airline is always pressurized, so there is no significant air venting on connection or disconnection.
while they might have trouble getting a facility to test it, they could address the myth of the car pulling the gas pump away and leaving a fountain of gas. (trouble, because they couldn't do it at an actual gas station because of the damage to the breakaway hardware and the risk of the hardware failing and having an actual spill - and the gas station wouldn't let them use water) on the other hand, they could probably get used pumps pretty cheaply and build their own dummy gas station.
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Post by c64 on Sept 22, 2014 15:38:09 GMT
There are several myths, especially about the gas pumps.
The Mythbusters could visit random gas stations and compare their bill with what they actually get. They could also check the accuracy of the air pumps as well.
Most gas pumps use a star of little piston pumps with a crank in the middle. Each piston injects a specific amount of gas into the hose with the nozzle. To adjust the pump, the slack of individual pistons can be set greater or tighter. This usually isn't done evenly. So when you only pump little amounts each time like the myth for saving weight as fuel says, the chances to stop after "short" pistons adds up and you get less fuel than pumping the same amount all in once and top up your gas tank.
Each piston creates an impulse for the counter. Cell phones might be able to add extra impulses to the counter. Another good reason not to use a cell phone while pumping gas. According to the federal German gauging office, this works for supermarket scales for sure! They registered up to 50% higher readings when a cell phone is "talking" close to the scale.
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Post by Cybermortis on Sept 22, 2014 16:43:50 GMT
C64; Do you have any links for the claim about cell phones affecting scales?
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Post by craighudson on Sept 22, 2014 17:42:26 GMT
Another good reason not to use a cell phone while pumping gas. What other good reason is there? Good being defined as not busted by the MB's
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Post by the light works on Sept 22, 2014 23:41:57 GMT
Another good reason not to use a cell phone while pumping gas. What other good reason is there? Good being defined as not busted by the MB's it makes you look like a tool? especially if your conversation is more important than the fact that your pump clicked off 10 minutes ago?
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Post by GTCGreg on Sept 23, 2014 0:53:53 GMT
What other good reason is there? Good being defined as not busted by the MB's it makes you look like a tool? especially if your conversation is more important than the fact that your pump clicked off 10 minutes ago? I know cell phones can't ignite gas vapors as static discharge has been shown to do, but what about a lit cigarette? I've seen a number of people, usually women for some reason, filling up while puffing on a cigarette. Even holding it in the same hand as the gas nozzle while taking it out of the car. I can't imagine someone being that stupid but they are. I even asked one woman that was filling up next to me to please put out the cigarette. All she did was call me an unrepeatable name and kept right on puffing.
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Post by the light works on Sept 23, 2014 1:08:14 GMT
it makes you look like a tool? especially if your conversation is more important than the fact that your pump clicked off 10 minutes ago? I know cell phones can't ignite gas vapors as static discharge has been shown to do, but what about a lit cigarette? I've seen a number of people, usually women for some reason, filling up while puffing on a cigarette. Even holding it in the same hand as the gas nozzle while taking it out of the car. I can't imagine someone being that stupid but they are. I even asked one woman that was filling up next to me to please put out the cigarette. All she did was call me an unrepeatable name and kept right on puffing. they tried lighting a puddle of gas with a cigarette, and failed. not sure if you could get the sweet spot without doing something extreme. a lighter or match would be a higher likelihood. I see quite a few people shut the pump off and the "drain the hose" - that might be worth testing.
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Post by GTCGreg on Sept 23, 2014 1:14:03 GMT
I see quite a few people shut the pump off and the "drain the hose" - that might be worth testing. Don't think you can do that on most pumps anymore. With all of the pumps I've used, as soon as the pressure in the hose drops, the nozzle will no longer stay open. You may get a few drops but that's about it.
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Post by silverdragon on Sept 23, 2014 6:03:59 GMT
And walk into a legal minefield.... Caution. In this country, all gas stations are required by law to calibrate pumps regularly, if you find they are under-selling a gallon, you are questioning their legal requirements. This may be true elsewhere.....
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Post by silverdragon on Sept 23, 2014 6:06:56 GMT
Air pumps, ££ paid-for coin operated ones.
Anyone yet managed to get all round and do all four corners on your 20p?.. or whatever coin it takes where you are....?..
I suspect a conspiracy to steal an extra 20p, as you cant just check three tyres can you?... Someone has timed the average it takes to do 4 tyres and subtracted a quarter of that on the time allotted to 20p.
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Post by GTCGreg on Sept 23, 2014 14:27:54 GMT
And walk into a legal minefield.... Caution. In this country, all gas stations are required by law to calibrate pumps regularly, if you find they are under-selling a gallon, you are questioning their legal requirements. This may be true elsewhere..... And? Are you not allowed to question if they are following the law?
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Post by Cybermortis on Sept 23, 2014 14:48:57 GMT
You are not allowed to show footage of the gas stations without the companies permission, or unless an investigation has/had been carried out to confirm wrong-doing. Otherwise the show would be sued.
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Post by the light works on Sept 23, 2014 15:29:30 GMT
You are not allowed to show footage of the gas stations without the companies permission, or unless an investigation has/had been carried out to confirm wrong-doing. Otherwise the show would be sued. just the same as you can't go around accusing random people of being crooks. in the US, the department of weights and measures checks the calibration - and if it is off AT ALL, they give the station owner a week to fix it. by AT ALL, I mean they have a calibrated 5 gallon can, and it has to come within visual error of the 5 gallon line on a 4 inch diameter column. if it passes, you get a certification sticker that is good for a year, and the calibration wheel gets a fresh security seal. they test the pumps both at minimum flow and at maximum flow.
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Post by GTCGreg on Sept 23, 2014 17:20:32 GMT
You are not allowed to show footage of the gas stations without the companies permission, or unless an investigation has/had been carried out to confirm wrong-doing. Otherwise the show would be sued. Doesn't seem to stop news crews.
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