Vacuum pump performance difference... (evacuation time to say... 150 micron)

[jinu117]

I currently have old leybold d2a got it from friend for cheap so I am not complaining (I tested it to see it pulling down to about 18 micron after.... LONG time :P)
I believe this is one of really good vacuum pump originally used for lab work etc but the problem is... it's 2CFM can get underwhelming at times :P And to be able to block out pump and keep the vacuum gauge read if I want some fine diagnosing, it will cost me another $50-60 for those evac manifold stuff for vac pump.
I have been eyeing some 4-6cfm vacuum pump (more in 6cfm range) of robinair, yellow jacket, j/b and was wondering how faster of vacuum time I will have in single stage with these pump vs what I have now to get to 150 micron or so?
Would appreciate some inputs since you guys must have used many vacuum pumps over time.

[star882]

Tip: Use an old compressor to pull down part of the vacuum, then close the valves on the gauge, switch to your vacuum pump, turn it on, open the valves, and continue.
This way, the vacuum pump does not have to pull it down all the way from air pressure. It also helps to do the vacuuming with the system in a warm place, so any remaining air and moisture expand making it easier for the pump to remove.

[wdrzal]

in a single stage there is about 1/8 to 1/4 cubic foot of internal volume ,Im just guesing I didn't do the calculations, but a 1 cfm pump would lower the pressure in about 15 to 45 seconds.. you just need to lower the pressure and KEEP it there and let it pump until all the moisture is removed. I use a 6 cfm pump on systems from 250,000 to 500,000 btu's and it does just fine .do you really think you need a 6 cfm for 600 btu's., NOT. its the pumps abilty to reach and maintain a low micron readind that is important.

want to add on these small systems a 10cfm pump won't evacuate a system any faster than a 1 cfm. What is important is to remove restrictions as that pressure loss is critical at very low pressures. Use the largest diameter hose of the shortest length for dehydrating.I all ways remove the valve core also ,that is a major restriction that lengthens evac times substantully.

[jinu117]

in a single stage there is about 1/8 to 1/4 cubic foot of internal volume ,Im just guesing I didn't do the calculations, but a 1 cfm pump would lower the pressure in about 15 to 45 seconds.. you just need to lower the pressure and KEEP it there and let it pump until all the moisture is removed. I use a 6 cfm pump on systems from 250,000 to 500,000 btu's and it does just fine .do you really think you need a 6 cfm for 600 btu's., NOT. its the pumps abilty to reach and maintain a low micron readind that is important.

want to add on these small systems a 10cfm pump won't evacuate a system any faster than a 1 cfm. What is important is to remove restrictions as that pressure loss is critical at very low pressures. Use the largest diameter hose of the shortest length for dehydrating.I all ways remove the valve core also ,that is a major restriction that lengthens evac times substantully.

Gotcha. I did notice immediate improvement when I got my 4 valve manifold with 3/8 fitting. Vavle core removal tool might be something I pickup on next time I guess. It isn't overtly lengthy to triple evac (other than first one for obvious reasons) but still I thought where ever I can save time, it would be good. right now whole process down to 200 micron first evac, 150 2nd evac, 100 last evac takes about 2 to 2.5 hours total. I was hoping to reduce it down to about 1 to 1.5 hours if possible. But from sound of it, that is no go even if I get high CFM vacuum pump. So removing valve core will improve the time significantly? (I an thinking about those valve core remover that doesn't leak refrigerant out after your explanation)

[wdrzal]

evac time is mostly determined by the amount of moisture in a system, it doesn't take long to remove the air and pump down to 2000 microns, its the next 1500 to 1700 . If your carful during assemble and purdge with dry nitrogen it reduces time.If you pump a system down to 300 to 500 microns your good to go.because of the oil in the compressor its hard to get below 250 to 300 microns.the free floating water vapor is easy to evacuate,its the water molacules that are adhearing to the copper that are harder to remove. surface tension creates a mechanical bond to the copper and they don't want to let go. That where heat helps, its like giving them a kick to let go and get their ass moving towards the pump.

[jinu117]

evac time is mostly determined by the amount of moisture in a system, it doesn't take long to remove the air and pump down to 2000 microns, its the next 1500 to 1700 . If your carful during assemble and purdge with dry nitrogen it reduces time.If you pump a system down to 300 to 500 microns your good to go.because of the oil in the compressor its hard to get below 250 to 300 microns.the free floating water vapor is easy to evacuate,its the water molacules that are adhearing to the copper that are harder to remove. surface tension creates a mechanical bond to the copper and they don't want to let go. That where heat helps, its like giving them a kick to let go and get their ass moving towards the pump.

NOW... that explains it much better than some things I've heard
Time to get that small heat blanket I had from somewhere
Thank you again for my #1 helper hehe....