Tag: micron


To answer the question in the title, it is a measurement of pressure, but REALLY it is a measurement of distance.

First, any scale CAN be used to measure vacuum (negative pressure) as well as positive pressure. The trick is knowing which is best suited for which and the size of the scale. Larger units of measure are better suited for higher pressure and greater differentials, smaller units of measure are better suited for lower pressures or smaller more critical differentials.

A Micron of Mercury (or micron) is a very small/fine unit of measure related to the displacement of a mercury column by atmospheric pressure thus the distance part. In fact, a micron is one-millionth of a meter of mercury displacement. That’s a tiny amount of pressure.

Inches of Mercury is a more rough measure of pressure, usually vacuum or even barometric pressure or altitude. Inches of Mercury is represented by the abbreviation HG

1 HG is equal to .491 PSI or roughly 1/2 of a PSI.

The force of the atmosphere around us is equal to 29.92 inches of mercury or hg or 14.7 PSIA Therefore a perfect vacuum can be thought of as 0 hg although a “perfect” vacuum can never be achieved.

When we read pressure as a tech with a gauge we read it in PSIG which means it is already set to zero at 14.7 PSIA and 29.92 hg.

So in the case of the suction/compound / blue gauge when it goes into a vacuum it reads in the “negative” hg scale down to -29.92 because it is PSIG, not PSIA.

1 inch of mercury (HG)  is equal to 25,400 microns (of mercury)

In the micron vacuum scale, we start at 760,000 microns at sea level atmospheric pressure and work down towards a perfect vacuum of 0 microns or 0 hg. This is why a lower # in the micron vacuum scale equals a better / deeper vacuum, a higher number equals a worse / less deep vacuum.

This shows why pulling a deep vacuum is done in microns, it is a very fine measurement that provides very detailed results. This is why very small changes can make such a huge difference in the micron reading on a micron gauge.

It also shows why micron gauges can seem finicky. They are really precise instruments.

— Bryan

When evacuating, the FASTEST way is to use two large diameter hoses connected to two core removal tools and the cores removed. These hoses are then connected to the pump using a tee or evacuation “tree”.

However, when you only have one large hose another acceptable method is to connect the large hose to the suction side and the vacuum gauge to the liquid side alone.

Brad Hicks from HVAC in SC made a nice little video showing how he does this with just one hose. He uses a core tool with the vacuum gauge on the liquid line to ensure that there aren’t and issues with depressing the core, which happens often with certain cores and gauge couplers. The other reason is so that he can valve off the vacuum gauge when he releases the charge or charges the unit to prevent refrigerant and oil from potentially entering his vacuum gauge.

The disadvantage of this setup is that the vacuum must all pull through the metering device which can add time to the process. In the case of a “hard shut off” TXV this method may not work.

Transcript

Well guys here’s another 60-second tech tip video. This one’s going to be on single hose evacuation setups. I get tons of questions on the subject so hopefully, this will clear things up a little bit. It’s very very simple, all I have is two valve core removers here both ports liquid and suction have been removed. On the liquid side, I’ll have my micron gauge. In this case the BluVac Pro and on the suction side I have my Appion hose. This is a six foot(1.82 meters), 1/2″ diameter 1/4″ by 3/8″ and then, of course, my vacuum pump. No special fittings or anything anywhere very very simple setup and very effective. Just to give you an idea I’ve been running a total of 24 minutes right now and my decay test has another two minutes I’ve set for 10 minutes a day so another two minutes and we’ll be good to go and as you can see single hose setup very very effective and as you can see I have it isolated. I’m still reading my micron gauge and everything in the system.  Hope that helps just a quick rundown have any questions feel free to ask.
— Brad Hicks, HVAC in SC
Scroll to top
Translate »

Daily Tech Tip

Get the (near) daily Tech Tip email right in your inbox!
Email address
Name