Newbie micron question

[The Bossman]

Just how many microns should my to-be-purchased vacuum pump be able to pull? The one I'm looking at says 70. Is that gonna be enough?

How low do you guys go before turning off the pump?
I will be getting a micron gauge as well.

[Stewie007]

70 Microns is enough. These types of systems are beste at 200 Microns and below.

As far as the length of the evacuation, it varies per system. It could take all night, or it could take a few hours. It depends on the quality of the pump, age of the pump, cfm rating of the pump, and the oil level. Too high or two low in oil makes for less performance.

Anyways, don't ask for a Micron Gauge at the A/C store, it might confuse them. :p Just ask for a vacuum gauge. The one I have is blue, and reads in PSIA, Torr, mTorr, Microns, Pascals, InHG, and I think one other unit; not sure though.

[wdrzal]

ASRAE (american society of refrigeration & Air conditioning engineers) recomends a vacuum of at least 1500 micron but a lower one is preferable. I like to always get to 500 microns and 250 to 300 is about the best you will get in a system in the field.So a pump rated to 70 is ok. Keep in mind a 2 stage pump is better than a single stage one,but are more expensive. Also keep in mind that vacuum pumps wear out,if buying a used one I would stay away from any that look like they have a lot of wear, but one used in a lab enviorment could look like new but have been run for 24/7 and be worn also. If buying used ask how the pump was used, look at condition and ask if they know what micron reading it will pump to currently, this may be different than new specs. Having said that there are a lot of people who bought pumps and used them very little and are like new,just use your head and take every thing into consideration.

[Stewie007]

Thing about buying them used is you never know what kind of owner it had. People like me perform routine maintenance. This includes at least opening her up and cleaning out the reservoir. I recently disassembled mine and cleaned it out quite well. Inspected the seals, assured that all moving parts were in good order and freely able to move.

If you're dealing with a new system, you should be able get under 200 Microns. I find that the pump out assemblies I've built at won't hold a vac well unless you get it under 200 Microns. They're small systems, round about the same size as these, just a bit bigger.

Evaluate how often you will use it. And decide whether to buy one new for about 260 bucks, or to try to get a good deal elsewhere. I got my two stage from Ebay, and it works quite well. Although, it should work alot better now that its all clean. :)

When you do evac, don't just pump her down and get right to business. Test your vac. When you've got a deep vac, close off the manifold THEN turn off your pump. Let the system stand for 10 minutes. If you have a good vac, the gauge should not climb any more than 200 Microns in 10 minutes. Give it 20 minutes, even. If it hasn't risen beyond that point, you've got a good vac. You see, when you take the pump off the circuit, the vacuum will have to "settle." If you've got a real good vac, it won't climb much at all. If you don't, those numbers will count off like nobody's business, at which point you engage the vac once again.