Vacuum guage

[GENERALCOOL]

Dear Friends,

When I use vacuum pump and see suction gauge it comes to -26 PSI (and -30PSI at cities that altitude is zero means near sea) and it means pressure of inside of pipes is less than ambient pressure but yesterday I saw a video on "Youtube" someone started his vacuum pump and after couple of hours he showed that his system pressure is "500 micron" and told it is enough and we can turn vacuum pump off.
I know "micron" is one of pressure units but it is above zero not below zero. What is -26 PSI and what is +500 micron ??
It we can not reach to 0 microns never, What is -26 PSI on suction pressure gauge during vacuuming? Finally we can go below ambient pressure via vacuum pump or it is not possible ?

Thanks.

http://www.generalcooltrade.com

[Brian_UK]

I think you are mistaking your gauge scales. A manifold gauge will start at 0 psig and increase to 250psig. If you start a vacuum the manifold gauge will read below 0psig and the scale changes to "hg with the maximum shown as -30"hg.

If you look at the chart shown at this link -> https://www.engineeringtoolbox.com/v...ter-d_460.html it should help you understand the different scales used.

[NH3LVR]

Just to clear up some confusion:

Some years ago a employer sent me to a vacuum class. (Not refrigeration oriented)
I was confused at first and questioned the instructor. He instantly recognized I had a refrigeration background.

We start at ambient pressure. (0 pounds) with our gauges. Anything less than that is minus. (- 28 inches.)

When we use a micron gauge we are going up from absolute zero. (500 microns is closer to absolute zero vacuum than 1000 microns)

The scale below zero on your gauges is in inches of vacuum (inches of mercury), not pounds.

[RANGER1]

https://www.contractingbusiness.com/...e-clockwatcher

https://www.trutechtools.com/Vacuum-...ng_c_1100.html

This link seems to be pretty good at explaining things.

[GENERALCOOL]

very clear and very nice, Thanks friends

[Topher Co]

I finally have all my technicians using digital micron gauges on every vacuum. They have proven priceless. We should never have leaking solder joint again, and the units are that much more protected as a whole. Tech like digital micrometers allow us to offer the best service for our customers. It is so worth leaning and becoming proficient at.