Calibrate a tire pressure gauge?

[vavet]

Ever try to get a tire pressure gauge calibrated? Or even just measured so you know how far off it is?
I used the compressor at Sheetz a few days ago and verified with the pencil style gauge I keep in my car. I checked with my service style unit (combination filler and gauge) similar to this one when I got home.

https://www.amazon.com/dp/B0002SRL20/?tag=atomicindus08-20

i don’t even need any adjustments made so it reads correctly if I just know that a reading of 37 is actually 35.
what kind of shop would have a standard for comparison?

 

[Meursault74]

Nope. Going about it wrong. You'd need to buy a "calibrated manometer". Connect/adjust a compressed air source and check it with the calibrated manometer. Then once that's set, check the tire gauge with it and see how far off it is.

I have to use a 'calibrated manometer" for scientific work. Calibration service with paperwork is $200-300. about 75% of the cost of the unit.

I highly doubt any tire shop is going through this expense. I had one unit that was never out of calibration specs in over 10 years of use, but it still had to be sent out to be checked for regulatory purposes.

2 psi @ 35 psi is less than 10% variance, good enough for 99.99% of the population.

You'll likely get higher difference reading between the side of the car facing the sun and the side in the shade.

 

[RTM]

I'm with Mersault. I doubt Sheetz is even +/-20%, with all the people that probably abuse it, drop it, drive over it, etc. I have access to guys with all the calibration tools at work. When they calibrate my gauges, I drag my good one in every few years, just to find it's very close to what they just calibrated. I don't drag the pencil ones in, only my dial. The pencil type is way less close IMO than my dial.

 

[bbbarracuda]

I think the most important thing is the consistency from tire to tire.

2 psi @ 35 psi is less than 10% variance, good enough for 99.99% of the population.

I agree with this, I bet it is a rare place that would pay to calibrate an air gauge, unless it a race team or similar where tenths of pound make a difference.

 

[HenryAZ]

I have a half dozen or so Milton stick gauges in different psi ranges. I check them against each other, and usually they all read the same, so I call that good. Once in a while I have gotten a flyer. Miltons are cheap enough I just tossed it and bought another. It matched up with my others.

 

[dnschmidt]

The only time that accuracy was needed was on the Corvair which if the front and rear tire pressures were not at the correct level the car, as Ralph Nader stated: "Was unsafe at any speed." Dumb *** GM thinking that Americans would monitor their tire pressures.

 

[engineer2]

You can do an internet search for a "metrology lab" in your area that does pressure calibration. The cost would likely be more than the cost of a new gauge.

I've had a few cheap Chinese gauges tested at work and they are usually accurate to about ±0.5 psi at room temperature.
±2 psi accuracy is adequate for most passenger car tires as long as the gauge reads consistently.

 

[Wrench97]

These are what we used> https://www.amazon.com/dp/B07Q5H7HG5/?tag=atomicindus08-20
Once a week they needed to checked and adjusted on the master calibration station, which was a air regulator set to 100 psi and a liquid filled gauge. I had the pleasure of calibrating the master once every 90 days since I knew how to use the manometer left over from the Detroit Diesel tool kit...................................................

 

[Meursault74]

These are what we used> https://www.amazon.com/dp/B07Q5H7HG5/?tag=atomicindus08-20
Once a week they needed to checked and adjusted on the master calibration station, which was a air regulator set to 100 psi and a liquid filled gauge. I had the pleasure of calibrating the master once every 90 days since I knew how to use the manometer left over from the Detroit Diesel tool kit...................................................

How often was the manometer checked/calibrated ?

 

[Walkers]

How often was the manometer checked/calibrated ?

We checked ours quarterly, and the standard we checked against was sent off annually.

 

[Walkers]

Ever try to get a tire pressure gauge calibrated? Or even just measured so you know how far off it is?
I used the compressor at Sheetz a few days ago and verified with the pencil style gauge I keep in my car. I checked with my service style unit (combination filler and gauge) similar to this one when I got home.

https://www.amazon.com/dp/B0002SRL20/?tag=atomicindus08-20

i don’t even need any adjustments made so it reads correctly if I just know that a reading of 37 is actually 35.
what kind of shop would have a standard for comparison?

Most cars these days have tire sensors that are pretty accurate, especially when not running, but has been through a few samples ( Cars on in the mornings warming up, but tires have not changed yet). So let your tires get stable, and check your gauge against them.

 

[gte718p]

ou can do an internet search for a "metrology lab" in your area that does pressure calibration. The cost would likely be more than the cost of a new gauge.

I've had a few cheap Chinese gauges tested at work and they are usually accurate to about ±0.5 psi at room temperature.
±2 psi accuracy is adequate for most passenger car tires as long as the gauge reads consistently.

We had calibrated gauges when I worked at the race shop and I had them in my last plant. Calibration was required annually. At the race shop we sent them out. For the ship, we could calibrate them ourselves. Even doing it our self the cost was more then the price of the gauge. Unless it has been abused 95%+ of the ones we tested were within 3-5%. That may or may not be acceptable for you. For a DD, as long as they are all the same, you will probably not notice the difference between 33 psi and 35 psi. A top quality race car drive would lose his $hit if his tires were off that much.

 

[ambenz]

I want to revise this old thread as I have 2 Milton inflation gauges and a round Sata inflation gauge....


....and according to my 2020 Ford Edge, all my gauges need to read 5 pounds over the recommended pressure the Edge reads on its information display, on the dash when the tires are at operating temperature! Make me think I have to over inflate my vehicles tires just so my vehicles display will read correctly and the wife will not question the reading. It also seems that the tire shop sets tire pressure on the car display as they came back reading correct on the vehicle display.
So I HAVE to assume my gauges are not reading correctly based on what I see. Can I adjust the readings on these gauges to match/calibrate it to the vehicles display reading? Looking at the Miltons, I do not see what I can do to adjust the scale. The round one I may have to remove the plastic on the back cover to find a adjustment screw. Anyone know how to adjust/calibrate these gauges so I can be confident the vehicle will read the correct pressure after I add air to the tires?

 

[SwissMetric]

As pressure calibrators are very expensive, I'd simply check a tyre at various gas stations using the calibrated manometer of the mobile air tank. That said, here air is nearly always free and you often use a small mobile device with an integrated tank, but I remember that in the U.S. you had often to pay for air.

The accuracy of the effective pressure is not that critical, I'd pay more attention to left/right tyre pressure deviations.
A slight overpressure is less dangerous than underpressure and I'd also periodically visually check tyres, especially for cracks.

 

[Wrench97]

I want to revise this old thread as I have 2 Milton inflation gauges and a round Sata inflation gauge....


....and according to my 2020 Ford Edge, all my gauges need to read 5 pounds over the recommended pressure the Edge reads on its information display, on the dash when the tires are at operating temperature! Make me think I have to over inflate my vehicles tires just so my vehicles display will read correctly and the wife will not question the reading. It also seems that the tire shop sets tire pressure on the car display as they came back reading correct on the vehicle display.
So I HAVE to assume my gauges are not reading correctly based on what I see. Can I adjust the readings on these gauges to match/calibrate it to the vehicles display reading? Looking at the Miltons, I do not see what I can do to adjust the scale. The round one I may have to remove the plastic on the back cover to find a adjustment screw. Anyone know how to adjust/calibrate these gauges so I can be confident the vehicle will read the correct pressure after I add air to the tires?

All 3 of your gauges read the same?
Is so I'd think the Focus is off.

 

[vavet]

As pressure calibrators are very expensive, I'd simply check a tyre at various gas stations using the calibrated manometer of the mobile air tank. That said, here air is nearly always free and you often use a small mobile device with an integrated tank, but I remember that in the U.S. you had often to pay for air.

it used to be free, but now most places make you pay. Do you know why?

inflation

I’ll see myself out.

 

[BrandonV]

....and according to my 2020 Ford Edge, all my gauges need to read 5 pounds over the recommended pressure the Edge reads on its information display, on the dash when the tires are at operating temperature!

Are you filling up cold?

Right now, for example, Phoenix can experience a temperature shift from the low 40s to the high 70s. I fill up my car's tires to 33 psi in the morning when they're cold, but by the time I get home from work, they usually reach around 38 psi because the temperature is 30 degrees higher and the tires are warmer from the drive.

 

[Meursault74]

it used to be free, but now most places make you pay. Do you know why?

inflation

I’ll see myself out.

It's still free here.



Oh, you want it pressurized above atmospheric pressure for your tires. Sorry the compressor is out of order, we've sent in a work order to have it fixed. Feel free to take all the air you want from the surroundings for your internal combustion engine though.

I can't remember the last time I filled my tires anywhere but my garage at home or with the small compressor I have the plugs into the lighter outlets in the car.

Probably last century when I worked for a service station and we had to have air working to use at full serve.

 

[nadogail]

Only on Garage Journal would I find a discussion about how to spend 2 or 3 times the replacement cost of calibrating a gauge that is seldom used.
Most tire pressure gauges are only rarely used.

 

[zendriver]

Used pencil types on and off for 50 years and never really trusted their accuracy.

Now it's either close enough or use two or three different gauges and average out.

 

[bwringer]

Limber up your "mute" button finger, everyone's favorite yelly guy at Project Farm has an answer for you...

Skip to 18:50 for the chart.

He did some decent science here, buying two samples of each gauge and testing against a calibrated gauge. The #2 Merlin and #1 Jaco gauges appear to use nearly identical electronics, but who knows.

Anyhoo, I have the #2 winner, the Merlin digital gauge from HF. Mine was under $20; not sure if they went down in price or what. It agrees with a dial gauge and another electronic gauge.

My other gauges are all pretty close. However, I've found that the auto shutoff on a couple of battery powered pumps is reliably off by three or four PSI. In other words, if I want 33psi, I need to set it for 36 - 37psi.

 

[Leaflessshadetree]

I want to revise this old thread as I have 2 Milton inflation gauges and a round Sata inflation gauge....


....and according to my 2020 Ford Edge, all my gauges need to read 5 pounds over the recommended pressure the Edge reads on its information display, on the dash when the tires are at operating temperature! Make me think I have to over inflate my vehicles tires just so my vehicles display will read correctly and the wife will not question the reading. It also seems that the tire shop sets tire pressure on the car display as they came back reading correct on the vehicle display.
So I HAVE to assume my gauges are not reading correctly based on what I see. Can I adjust the readings on these gauges to match/calibrate it to the vehicles display reading? Looking at the Miltons, I do not see what I can do to adjust the scale. The round one I may have to remove the plastic on the back cover to find a adjustment screw. Anyone know how to adjust/calibrate these gauges so I can be confident the vehicle will read the correct pressure after I add air to the tires?

My inflators (I have several) seem to read a few PSI higher than my TPMS systems in my cars/trucks. Most of my gages (dial, pencil or digital) agree with the TPMS.
If I overinflate slightly and use the inflator to bleed off pressure from the tire they seem to be closer.

 

[SwissMetric]

I didn't know that in CA air had to be free, usually I'm stricly against overregulation but that rule makes sense.

Here in most cases you've just those portable devices which are always free. I believe there are a few stations where you have stand-alone systems with integrated compressor where you pay with coins but I've never used any.
In some cases you've a hose with a fixed connection supplied by central compressor.

The cheap Chinese electronic manometer failed before I used it the 1st time. The cheap mechanical indicator I bought in the U.S. was funny as the flat stick with the psi scale ticks had so much friction that I never trusted it, massive stick-slip is no really great in such case.

Overall I just rely on the manometers of the gas station devices and if I suspect something fishy I check it again with some another device.

 

[Wrench97]

We use to leave one out years ago but after the second one got cut off and stolen that ended that.
Seems to still be a issue I've seen plenty of 24 hr gas stations missing hoses also lately.........

 

[FigN⋅m]

Random side note:
Gas station I used to frequent years n years ago showed me a lil secret...
Press the coin return button repeatedly about 10 times or so and it will turn on.
Now, I don't even know if the air machines even use coins anymore, but
it's worth a try next time you're needing to use one for a quick fill up.

 

[SwissMetric]

We use to leave one out years ago but after the second one got cut off and stolen that ended that.
Seems to still be a issue I've seen plenty of 24 hr gas stations missing hoses also lately.........

Sorry for this OT reply (moderators can delete it) but as I was the first time in the U.S. I was very surprised to have to pay *BEFORE* filling up and also there were 24/7 opened gas stations everywhere, don't know if there is a single one left in Switzerland. Two had to close due to some stupid local regulations and for the highways I don't know (there was one but the opening hours changed), those should be avoided anyway as most are quite overpriced. Between around 22h00 (10PM) and 06h00 (6AM) you mostly can only use automatic systems where you can pay with cards and nearly always also with CHF (Swiss francs) and EUR (euros) bills.

More generally, paying anything in EUR in Switzerland should be avoided as the applied exchange rate is often a rip-off (and often some additional transaction fees), also when paying with a card, the payment should always be done in CHF and not EUR.

 

[BrandonV]

I was very surprised to have to pay *BEFORE* filling up

Honestly it was pretty much the norm to pay after until like the 2000s.

Just like the pump used to make you lift the little pump nozzle holder to start the pump.

Ah nostalga.

 

[LopezBart]

The way pressure gauges are calibrated is with a dead weight gauge tester... it uses weights that exert a force on a piston, which pressurizes a fluid to work the gauge. The weights are carefully made to exacting tolerances, and the piston was often spun to eliminate stiction. These are still available, but are quite expensive (likely because of low demand). Given today's accurate digital scales, making such a unit might be an interesting machining project for the terminally curious.

 

[SwissMetric]

Whatever floats ones boat:

Pressure Calibrators | Fluke Pressure Calibration Tools | Fluke

Fluke offers a wide range of pressure calibrators with precision pressure measurement from 15psi/1 bar to 10,000 psi/690 bar boasting 0.025% accuracy. See lineup.

www.fluke.com

Just as example.

In most cases where calibration is required the device is sent to a specialized company.

As random example the 2022 calibration pricelist of SR Technics (formerly once a Swiss Air division):

https://www.srtechnics.com/media/hyjjofmb/calibration_pricelist_en_2022.pdf

Mutliply CHF prices by roughly 1.1 for USD.

Depending on domains, annual calibrations are required due to some ISO QA requirements. In many cases it's mostly a rip-off.
E.g. if you're using 20 Fluke multimeters and all are within tolerance when compared internally, chances are that all meet the formal requirements. I mention Fluke as according to my own experience they hold calibration quite well, it's not about advertising, the Fluke PC software I know is... well... let's remain polite here but the Fluke multimeters I know are reliable.

Also calibrating high quality torque wrenches annually or after 5000 releases, whichever occurs first, is overkill unless conditions are severe or if there was some abuse like hard shocks, excessive dirt ingress or corrosion.

 

[Meursault74]

I didn't know that in CA air had to be free, usually I'm stricly against overregulation but that rule makes sense.

Here in most cases you've just those portable devices which are always free. I believe there are a few stations where you have stand-alone systems with integrated compressor where you pay with coins but I've never used any.
In some cases you've a hose with a fixed connection supplied by central compressor.

The cheap Chinese electronic manometer failed before I used it the 1st time. The cheap mechanical indicator I bought in the U.S. was funny as the flat stick with the psi scale ticks had so much friction that I never trusted it, massive stick-slip is no really great in such case.

Overall I just rely on the manometers of the gas station devices and if I suspect something fishy I check it again with some another device.

It's supposed to be free if you buy something. But not that many people know this. The stand alone machines take coins. I think you're supposed to ask the employee to turn it on for you if you quote the law, but if he's the only one inside a booth, he's doesn't have to come out.

I don't know for a fact, but I doubt any of it is enforced. I saw an "out of order" sign for months at the local gas station I purchase gas.

30 years ago I worked for a station that had service bays and air plumbed to the islands. People would help themselves to the air and treat the hose and nozzle very poorly, then complain when it was broken.

I have an air compressor in my garage (what GJ member doesn't?), so the point is mute for me at this time.

 

[theoldwizard1]

Accu-Gage re-calibrated 4 or 5 of their gauges for the cost of shipping.

 

[Qualitytools]

Limber up your "mute" button finger, everyone's favorite yelly guy at Project Farm has an answer for you...

Skip to 18:50 for the chart.

He did some decent science here, buying two samples of each gauge and testing against a calibrated gauge. The #2 Merlin and #1 Jaco gauges appear to use nearly identical electronics, but who knows.

Anyhoo, I have the #2 winner, the Merlin digital gauge from HF. Mine was under $20; not sure if they went down in price or what. It agrees with a dial gauge and another electronic gauge.

My other gauges are all pretty close. However, I've found that the auto shutoff on a couple of battery powered pumps is reliably off by three or four PSI. In other words, if I want 33psi, I need to set it for 36 - 37psi.

I saw that video a while back and opted for the $10 Etenwolf gauge. Thanks for sharing

 

[Shadowdog500]

I want to revise this old thread as I have 2 Milton inflation gauges and a round Sata inflation gauge....


....and according to my 2020 Ford Edge, all my gauges need to read 5 pounds over the recommended pressure the Edge reads on its information display, on the dash when the tires are at operating temperature! Make me think I have to over inflate my vehicles tires just so my vehicles display will read correctly and the wife will not question the reading. It also seems that the tire shop sets tire pressure on the car display as they came back reading correct on the vehicle display.
So I HAVE to assume my gauges are not reading correctly based on what I see. Can I adjust the readings on these gauges to match/calibrate it to the vehicles display reading? Looking at the Miltons, I do not see what I can do to adjust the scale. The round one I may have to remove the plastic on the back cover to find a adjustment screw. Anyone know how to adjust/calibrate these gauges so I can be confident the vehicle will read the correct pressure after I add air to the tires?

If all three of your gages read the same they are probably correct. Whatever you compared them to is probably wrong.

The Milton tire inflators are easy to adjust, but yours probably don’t need to be adjusted.

Here is the adjustment procedure :

 

[SwissMetric]

It's supposed to be free if you buy something. But not that many people know this. The stand alone machines take coins. I think you're supposed to ask the employee to turn it on for you if you quote the law, but if he's the only one inside a booth, he's doesn't have to come out.

I don't remember how it was handled, I'm not even sure if "pre-paying" was common in rural areas. As I drove the most miles in the U.S. gas was inexpensive, maybe 2.5 to 3 times cheaper than in Switzerland though it depends on states and even small cars were gaz guzzlers.

30 years ago I worked for a station that had service bays and air plumbed to the islands. People would help themselves to the air and treat the hose and nozzle very poorly, then complain when it was broken.

Here something like this is very common, just googled pics:

Tragbarer Reifenfüller - Lufttank 6l - Fülldruck bis 16 bar - mit Füllschlauch 8

- Das Reifenfüllgerät ist ortsunabhängig durch eingebauten Lufttank - Reifendruckprüfung von Zwillingsreifen und Motorradreifen 049044x

www.esska.de

Retractable hose weels with pistol grip often end damaged as most don't know how to lock/unlock it correctly. Some just let everything go and the hose stopping ball ends crashing against the body of the reel.

The portable devices as in the link are removed when the gas station is not attended and there is a central compressor, not each island is ncessearily equipped, often there are less devices than connections. I suppose there are mandatory periodic controls but I don't know details, seriously miscalibrated manometers are rare, it's more about the valve adapters and sometimes the + and - pushbutton valves.


.

 

[RPH]

+/-5%, well within the operator error range.