Sell me on 1/2" hoses...
OK, just picked up a shiny new vacuum pump because the 16 year old SuperEvac died on the job.
7CFM JB pump.
Now, my current evac rig is 2 - 3/8" hoses, 1 - 1/4" hose when needed and VCRTs.
Following 'rules of thumb' that I was taught and information gleaned from this site:
a 1/4" hoses flows approximately 0.6 to 0.7 CFM.
a 3/8" flows approximately 4 times what a 1/4" hose will.
So, giving the benefit of the doubt to the 1/4" hose, 0.7 x 4 = 2.8 CFM per 3/8" hose.
2.8 x 2 is 5.6. Add another 1/4" hoses and you're up to 6.3 CFM which is DANG close to the actual pumps capacity of 7 CFM.
Will a larger hose benefit me in any substantial way and WHY?
Been pricing them and I've got a hard time parting with the coin that they want for a 1/2" hose for dubious benefit.
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.
I use the biggest hose the system will allow. 99% of the time, it already has a 1/2" flare on it somewhere, so it's not a big deal. You need large hoses to move refrigerant out of 125# and 1000# cylinders anyway. On smaller stuff, I use the biggest hose that I can get away with, without using a ridiculous amount of bushings and creating leaks. I don't buy into the benefit of large hoses with small fittings on them.
The key to happiness is lower expectations.
Don't pick the fly crap out of the pepper.
ditto on the 1/2 vs 3/8. hardly enough diff on resi to make it wortgwhile.
back in the day, on industrial, i would and have always used 1/2 copper to the king and queen valves as well as the receiver since time is crucial here. In which case the 1/2 makes boku sense.
I Am gonna use the new 1/2 hose today along with a 3/8 on todays job.
my rig is 1/4,3/8 and 1/2.
JP I am going to try that new appion CRT today on evac, If I don't like it make me an off and include shipping.
Got it for the price of the 1/2 hose in a Mega Flow basic kit.
Remember with a vacuum hose, we are talking diameters, a 1/2" hose is 4 times faster than a 3/8" hose. Going to a 5/8" hose would be 10 times faster then the 3/8"
Originally Posted by jim bergmann
I've seen your videos and they show some pretty impressive pull downs.
Something I don't understands is that when you remove the valve core you are left with a fixed opening, 1/8 or so?. So by changing to a larger hoses but still using the same pump, I would think you would still have the same pressure drop across the fixed opening (valve core opening) and this would result in the same flow.
If it's the hose that is the restriction to flow. Would a short 8" X 1/4" hose improve the pull down as much as a 5' X 1/2" hose?
Don't mean to hijack the thread but I thought Jim could improve on it.
The question you are asking has a rather lengthy answer, but I will try to simplify it.
1) We are limited by physics, and maximum vacuum is -14.7 psi
2) When we get into a deep vacuum, the differential pressure that causes flow is very small. If the difference in pressure between the system and pump was 100 microns the pressure would be .0019 psi
100/51,715 = .0019 (psia x 51,715 = microns)
3) Air is a fluid, and has viscosity, although it is very small. it has resistance to flow.
4) Because the flow is so small, the friction created by the manifold and any hoses connected to it become a major factor in the rate that the gasses flow through it.
5) Larger shorter hoses create less friction ( less pressure drop) and more flow.
6) The limitations to evacuation speed are typically the evacuation rig. Increasing pump size on an undersized evacuation rig will have no increase in performance. (again limited to -14.7 psi)
The service port is like a toll booth( one lane) on the turnpike. Yes the cars slow down when they go through it, but as soon as they are out of the gate, the flow increases again. The way we make traffic flow better is to remove the restriction. Larger hoses are like adding more lanes.
Last edited by jim bergmann; 06-23-2012 at 11:08 PM.
Thanks that makes sense
Originally Posted by jim bergmann
good question .. in same boat, 2x 3/8 hoses, except with 6 CFM Robinair.
Originally Posted by jpsmith1cm
good news is already got 1/2in T flare fittings ... trying to justify costs of 2x 1/2in hoses
OK, I'm getting this, but here is the next hurdle for me to overcome...
I've got a rhythm to my work. A cadence, so to speak. Since I'm typically the 'start-up' guy, the brazing and pressure testing is done.
I hook up the pump and go. I've got wiring and programming to do before I even think about checking the vacuum. Once all of that stuff is done, then I go check vacuum, start the system and begin testing or charging it.
So, if I jump up to 1/2" hoses, I'm thinking that will just mean that it will sit in a deep vacuum longer.
Is there any benefit OTHER than speed of evacuation?
Originally Posted by jpsmith1cm
You mean you don't have the need for speed???
Originally Posted by Pascone10
I have the need for accurate, methodical and technically correct work.
Speed is not, nor has it ever been a very important factor in what I do.
Now, I'm not going to go back to evacuating through a 1/4" manifold with 1/4" low loss hoses and schraeders still installed but I'm not convinced yet that I need to drop a C-note on a pair of new 1/2" ID hoses.
Did a 100hp low temp with the 3/8 hoses....got done in good time.