Help! How Is Anyone Supposed To 'accurately" Read An Air Pressure Gauge Like This One?

I will be taking my DMV Driving Test in a few days. My question/s: The main question is in the topic: "How is anyone supposed to 'accurately" read an Air Pressure gauge like this one?"

Why would anyone make a gauge with 30 psi increments instead of the standard 10 psi?

It seems to me so absurd! 1/2 way between 90 and 120 is 115 for example, but a driver is supposed to be able to 'accurately' read 3 psi for the Static Leakage Test after, of course, 'accurately' reading the air pressure after the readings on the gauges have 'stabilized'.

On this gauge, where exactly is 100 psi, or 85 psi?... ...what about 140 psi?... ...or 20, and 45 psi?... ...etc.

Soulin, you're getting ahead of yourself. That is not the gauge that shows a loss of air pressure during the "Air Brake Test."

That guage indicates how much air pressure you're putting into the brake system by applying pressure with your foot to the brake pedal. The pressure on that guage will continuously change with any change you make in the pressure you are applying to the pedal.

You're overthinking this because you aren't even looking at the proper air pressure guage.

Slow down. They will show you how to do this in school.

Oooops, maybe you are already in school. You need to ask your instructor to show you which guages to watch for the test. That is not the correct one. You should have two other air pressure guages that show the stored air pressure in the air tanks. That's where you will determine if the pressure is leaking down.

You are way over thinking this. The gauge is set up for the numbers you need. 90, compressor comes on. 120, compressor cuts off. 60, warning buzzer comes on. 30, valves should pop.

As for the 3 psi, you aren’t actually measuring it, if the needle is holding steady after it’s stabilized, you’re good. If it’s dropping and you can notice it in that minute after it stabilized, you have a leak.

Actually, I'm mistaken. That is the proper guage. Go with Andhe78's response. He is dead on!

I'll go to bed now, and try to come back in here when I can make some sense!

As others have said, don't over think it.

This is what mine looks like.

Just as vague as the one you posted.

For the static leakage test your basically just watching to make sure the needle doesn't continue to drop as your holding the brake.

RE:

You are way over thinking this. The gauge is set up for the numbers you need. 90, compressor comes on. 120, compressor cuts off. 60, warning buzzer comes on. 30, valves should pop.

Actually not. CA CDL Manual says:

"*Air Compressor Governor Cut-In Pressure Test To perform this test, the air pressure for the vehicle cannot be rising when the engine is running. With the air pressure at maximum pressure (cut-out), begin slowly pumping the brake pedal to reduce the air tank pressure. Watch the air pressure gauge between pumps to identify when the compressor cuts-in (needle starts to rise). This must occur no lower than 85 psi for a bus, and no lower than 100 psi for trucks."

Just as vague as the one you posted.

Sure is albeit different and a 2-in-one single gauge. The one in the photo I took is just the primary, the secondary is exactly same except it has the number 2 instead of the number 1 on it.

For the static leakage test your basically just watching to make sure the needle doesn't continue to drop as your holding the brake.

It is a definite fail at the DMV on the Air Brake Test to press the "Service Brake" and reefer to it as the "Static Leakage Test".

Pressing the "Service Brake" and holding it down steady for 1 minute is the "Applied Leakage Test" on the "Service Brakes".

California DMV CDL Handbook says:

"Test Air Leakage Rate There are 2 tests as follows: Static Leakage Test With a basically fully-charged air system (within the effective operating range for the compressor), turn off the engine, release all brakes, and let the system settle (air gauge needle stops moving). Time for one minute. The air pressure should not drop more than: • 2 psi for single vehicles. • 3 psi for a combination of 2 vehicles. • 5 psi for a combination of 3 or more vehicles. Important: The maximum air loss rate for a combination of 2 or more vehicles is 2 psi if the towed vehicles are not equipped with air brakes. An air loss greater than those listed above, indicate a problem in the braking system and repairs are needed before operating the vehicle.

*Applied Leakage Test

To perform this test, the vehicle’s air pressure should be built up to maximum pressure (cut-out). With the air pressure built up, shut off the engine, chock the wheels if necessary, release the parking brake (all vehicles) and the tractor protection valve (combination vehicle), and firmly apply the foot brake. Then hold the foot brake for 1 minute after stabilization of the air gauge. Check the air gauge to see that the air pressure drops no more than 3 psi in 1 minute (single vehicle) or 4 psi in 1 minute (combination vehicle) and listen for air leaks. You must identify how much air the system lost and verbalize the maximum air loss rate allowed for your vehicle. • 3 psi for single vehicles. • 4 psi for a combination of 2 vehicles. • 6 psi for a combination of 3 or more vehicles. Important: The maximum air loss rate for a combination of 2 or more vehicles is 3 psi if the towed vehicles are not equipped with air brakes. An air loss greater than those listed above, indicates a problem in the braking system and repairs are needed before operating the vehicle. Note: For testing purposes, you must be able to demonstrate this test and verbalize the allowable air loss for your vehicle. If the air loss is too much, check for air leaks and fix any that are identified. For testing purposes, identify if the air loss rate is too much.

Just sayin.

Anyway I was hoping for someone who has experience with the specific gauge scale as what I have to test with to chime-in.

Thanks to all for trying... ... But no cigar

First off that gage is a precision instrument. The first line between 0 and 30 is the point your valves should pop. As far as measuring air loss on the test what andhe78 said is correct. Good luck. Also ask your instructors to explain it to you.

For the test your school will teach you exactly what to say. You must memorize it. You must understand it. Your instructors can explain that gage better. But the unmarked lines are the ones to look at. Some trucks have two gages some have one with two needles.