Checking pressure gauge calibration?

[TodFitch]

The gauge that I have been using to check my tire pressure has gone bad. . . The only reason I noticed is that with the tires cold the gauge was reading about 10 psi higher than I'd last filled them to. This time around, I used my most trusted air system gauge to set the hose pressure to what I wanted the tires to be and hooked the hose on each tire until I stopped hearing air movement.

 

But it got me thinking. For a temperature gauge I can get something to a known temperature (ice water, boiling water, etc.) and measure the temperature.

 

But I can't think of an easy way to verify the readings on a pressure gauge with things I have in the garage or house. Anybody have a way to do this that does not involve simply checking against another (assumed good) gauge?

[plymouthcranbrook]

I have 4 gauges. I just double checked with a couple of others if I feel an issue has occurred. I can't imagine why you would need to be more accurate that that.  After all the type of driving most of us do is not high profile enough to worry about a couple of pounds difference.

[TodFitch]

. . . I can't imagine why you would need to be more accurate that that. . .

Compulsive desire to have any gauge I have be accurate. Or, if not accurate then consistent with known correction.

 

But more to the point, simple curiosity on how this might be done without a fair amount of setup.

 

For example, I can imagine taking an old single ended brake cylinder, setting it so the piston moves vertically, placing a known weight on it, and pressurizing the system so the weight is suspended then measuring the pressure. But my car does not have single ended wheel cylinders. I have a spare master cylinder which I could measure the bore of and do the same type of thing.

 

In any case that is a bit more futzing than just checking a temperature sensor by measuring ice water and boiling water. And I probably won't do much more than use my old U.S. made industrial pressure gauge as the reference to check others against.

 

For tires, as long as the gauge is consistent you can adjust the fill up or down from your reference based on evidence of under or over inflation wear patterns. So having a perfectly calibrated gauge is not needed.

 

So you are right, it isn't a big deal. Mostly a matter of curiosity.

[Dave72dt]

I think water boils and freezes at different temp depending on humidity and altitude.  Don't quote me because I"m not 100% positive.  My old boss made a lot of maple syrup and would check the boiling point each day before he started to cook it down.  Those few degrees could make the difference between burning it or not. 

[Plymouthy Adams]

any gauge no matter the make or model or where you buy it needs always be tested against a calibrated standard....in the absence of a standard..it is guessing and though many are close enough one should have the actual +/- tolerance if possible.  I have found that the Milton inflators with built in gauge are very reliable units even after some 25+ years when last checked against my standard....

[Don Coatney]

Last year I bought 3 of these cheep china made stick gauges for about two bucks each. I keep one in each car. I have never checked accuracy but if they are within a couple of pounds that works for me. I just pump all 4 tires using the same gauge so all tires are equal.

 

[Niel Hoback]

Fortunately, the car I really care about tires on tells me the pressure continuously. Checking them with a Milton gauge shows the sender's as pretty accurate.

[48Dodger]

As the tires are heated up, they expand......not just the air, but the tire itself. In racing we measure the temp inside, middle and outer surface. Then we measure the tire size with a tire guage. Then we check the pressure. This helps choose the  location of the tires for the best peformance around the track (smaller tires in/ larger out). All tires grow differently under different stress stituation (ie more left turns then right). In other words.....setting your hose pressure and blowing air into the tires isn't enough. If your right front tire is set at 35 lbs cold and is 29 inches and your left set at 35 lbs and is 29 3/4.......you get the idea. Its like Don said,  "pump all 4 tires using the same gauge...." its a realtive calibration. But to be sure of performance.....measure tire growth after driving, to confirm the proper tire pressure for size. 

 

48D

 

temp

tire size

 

If I really wanted to create a standard for my tire pressure guages.....I would put a tire stem fitting on the end of a short air hose and hook it to my air compressor.

[TodFitch]

. . . If I really wanted to create a standard for my tire pressure gauges.....I would put a tire stem fitting on the end of a short air hose and hook it to my air compressor.

 

I can and have checked my tire gauge against the air system gauges. But that is simply checking one gauge against another with the assumption that the gauge(s) on your air compressor system are more accurate. I know that the gauge on my air compressor tank is close to but not exactly the same as the gauge on my air lines. And I know that the gauge on the pressure regulator is close to but not the same as my “reference gauge” (an older US made gauge that I’ve attached quick disconnect hose fittings to). Are any of those gauges accurate in an absolute sense? I have no idea. My inner compulsive would like to know, for example that gauge A readings are within +/-x% or +/-y PSI at 100 PSI.

 

With respect to tire pressure, the thing that got me thinking about this, I generally set the pressure by my gauge to what the owners manual specifies then watch for tire wear for signs of under or over inflation. If I see that then I adjust the pressure slightly as required and watch some more.