Ok.. Im probably not going to sell you here but I just bought (2) 1/2" diameter 1/4" x 3/8" fitting hoses 5' long.
Now Ive been using 3/8 hoses for some time now and I wanted to try and see how much faster these 1/2" hoses are.
I called Christian at Appion a few weeks ago. They ran an experiment on a 10 ton unit.
Their goal was to pull to 500 microns and record how long it took to get there.
with standard 1/4 hoses, cores removed 500 microns was reached in about an hour.
with 3/8" hoses, schrader valves pulled 500 microns was reached in 20 mins
with 1/2" hoses, schraders pulled 500 microns was achieved in 3 mins.
The interesting note here is the 1/2" hoses and 1/4" fittings on them!!
As far as your rule of thumbs.. HVAC RAT posted some info on youtube. Check that out. He is one on the reasons I bought 1/2" hoses.
According to a book from thermal engineering 3/8" hoses about 1.7 cfm at best..
Also while talking to Christian he explained that Pumps are rated at the CFM at atmospheric pressure! Obviously we are not at Atmospheric pressure for long.
Last week I did a quick experiment of my own. Brand new 50 lbs recovery cylinder. One 3/8" hose hooked up to the vapor port, micron gauge to the liquid. Pulled to 500 microns in about 15 mins. Swapped out that 3/8" for the 1/2" and guess what.... 500 microns in about 13-14 mins!!
So Im not sure what that tells me but I do recall Christian explaining CFM is not as important as having as many hoses as possible hooked up to allow the most options for the molecules to exit.. The bigger the diameter hose the easier it is for them to flow out..
I have a small 3 ton split I'm doing work on today. I will suck that down with one or two 1/2" hoses and see how long that takes..
Ill continue to use them and let you know what I find. I have a couple 30+ ton units to evacuate i believe this week..
Honestly tho I was expecting to pull that recovery cylinder down in half the time.. Oh well..
Also thank you Christian from Appion for taking the time on here and answering calls about this stuff. Its great to have a manufacturer share their knowledge with the end user.