Automotive Air Conditioning Information Forum

With all the talk in other thread about micron values, I'll be trying out a few Micron gauges to select one.

Interesting behavior with the two gauges I received so far. When Gauge A is connected to vacuum pump and Gauge B by a tee , Gauge A reads much lower.

VP Vacuum Pump
T tee
M microns

Gauge A - connected directly to VP = 1700m
Gauge B - connected by hose to VP (male fitting on Gauge B so hose is needed) = 1700m

Gauge A and B connected to flow-through T and then to VP by hose then A = 760 microns B = 1700m

I've tried it in various processes - having both on starting pump, having A on and then turning on B and vice-versa, etc. The result is that when A and B connected together to VP A reads lower...its like B affects the A reading.

One would think vacuum is vacuum but the readings are different when connected to same T.

Thoughts?

You start testing the tightness of a system by connecting a gauge directly to the pump, with no other fittings.
If the pump is a decent brand, with fresh oil, and the gauge is a decent brand, you should be at about 60 microns in one or two minutes. If this is not happening, then check the above parameters

There is no need to connect them in parallel. Test them individually.

So tested 10 different vacuum gauges, all directly to pump. Some from well known manufacturers. Some 2 different models from same (known) manufacturer.

Qne would think they'd all read the same....here are the readings

What is one to conclude when one can't trust their instruments?

Thoughts?

Gauge Microns
A 1940
B 2340
C 3300
D 2710
E 2800
F 124306
G 2900
H 4425
I 2180

Send it out for Calibration.

I have calibrated meters, gauges, micrometers and torque wrenches.

https://www.digivac.com/vacuum-gauge-ca ... -services/

IMO you have a leak somewhere, especially when F shows 124306.
Or the pump is NG.

I would try them on another pump

Another possibility is they are oil logged. Rinse with Isopropyl alcohol and dry well

All the gauges are brand new.

All of them were connected directly and only to the pump which was constantly running.

All of them got multiple tests.

All of them read differently.

I got that.
Re-read what I wrote. New doesn't mean anything anymore, clean them.
I suggested you try a different pump, you ignored that suggestion.
All you did was repeat what you already posted

I wonder if anyone on this forum can answer why an MFG of a product did not reach a specific spec. These are questions directly for the MFG of the product, IMO. I'm sure the phrase "laboratory Conditions" will be the response. I also think T-bird is correct on how an MFG would scale a test and how an independent doing a similar could show different results. We had both the CPS and the VG-64 in our shop. Both work as advertised.

Let's start a third thread on this topic.

tbirdtbird wrote: ↑Tue Oct 24, 2023 12:00 pm I suggested you try a different pump, you ignored that suggestion.

Different pump shouldn't matter.

To be clear, this is a test for consistency. If gauges were calibrated the same, they would all read the same no matter what pump they were on no matter what the vacuum level is.

As far as a pump reaching a certain target micron number that I would believe would be affected by pump condition and performance and altitude but what ever it can pull, that number should be the same on every gauge.

And one would think one wouldn't need to clean a new item.

The dilemma is, what gauge to believe?

I hoped a few would show the same so choosing any of those would be good bet and passing on the ones that read different readings.....outside of professional re-calibration which one would hope is not needed on a new item how is one to choose an accurate gauge?

Tim wrote: ↑Tue Oct 24, 2023 2:46 pm We had both the CPS and the VG-64 in our shop. Both work as advertised.

Let's start a third thread on this topic.

Those were in the test and read differently from each other....How did you know both worked as advertised?

IDK if the 3rd topic is a request or sarcasm, let me know.
If you want another topic started, can do that.
I did not see another micron gauge testing topic. Please provide the link and can move conversation there.
Thanks