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Thread: pulling a vacuum
08-22-2011, 10:04 PM #105
thinking out loud
Would it work to take a 1/4 x 1/4 x 1/2" flare tee with the two 1/4" copper lines going to the core removers and the 1/2" going straight to your vac pump?
08-22-2011, 10:24 PM #106
It would, but it would work even better if you went to 3/8 copper and a 3/8 x 3/8 x 1/2. Any size reduction or length is cap tube effect slowing down your evacuation ... has more affect than the capacity of your pump. For many years I used a 3.2 cfm pump ... with my big black hoses. Pump cfm only really matters on the part of the job you can see with mechanical gages ... after that they are almost all equal.
Any way you do the copper, you are going to be re-doing it often because of hardening. I remember one of my old instructors back in the 70's telling us one of his first jobs helping his dad many years before that, was making up a new set of 3 1/4" copper lines for his dad's manifold, every day.
Man up and buy the big black hosesSam
Know-it-all? Nope, not even half!
08-22-2011, 10:35 PM #107
08-23-2011, 04:06 AM #108
Are there any vacuum rated manifold gauge hoses that also work for a vacuum, or am I looking for something that doesn't exist?
I can find the black 3/8 to 3/8 quick connect hoses, but I can't find a 1/4 to 3/8. I have two C&D 1/4 core removers with the side tap for a ball valve and vacuum gauge. My DV-142n pump has one 1/4 and two 3/8 connectors, so running two 1/4 to 3/8 quick connect vacuum lines from the 1/4 core removers to the 3/8 vacuum pump seems to make the most sense.
Or should I get the 3/8 x 3/8 hose and get a 1/4F to 3/8M adapter like the YJ 19102 to connect it to the 1/4 core remover, but that has a core depressor and I don't know if that will work on the end of the core remover.
08-23-2011, 07:45 AM #109
08-23-2011, 07:45 AM #110
they have every possible hose on that site.
08-23-2011, 07:58 AM #111
Thanks for the link to the vacuum hoses!
Can you blankoff the hoses at your vacuum pump and hold the vacuum, ie, the hoses dont premeate like the charging hoses do, or do you have to blankoff with the core remover ball valves to hold the vacuum? Just wondering how much leakage there is on the vacuum rated hose compared to the standard charging hoses. I've tried to hold a vacuum on charging hoses, but it usually creeps up to 700 to 800 microns.
08-23-2011, 08:05 AM #112
The isolation valves on vacuum pumps are not entirely leak free they are to isolate the pump during oil changes so that vacuum is not entirely lost.Aircraft Mechanical Accessories Technician. The Air Force changed the job title to Air Craft Environmental Systems Technician. But I've decided I'll always be a Mech Acc.
08-23-2011, 08:26 AM #113
There are manifold trees (yes I meant TREE) to put at your pump that have valves for blanking off. I think Robinair and JB both make them in several styles.
I haven't checked lately but there used to be 2 grades of vacuum hose ... the fat black hose and metal hose with o-ring ends. The black hose has always held for me working in the 700 to 900 range for an hour. The metal hoses are very expensive and I never bought them. I think Robinair has them in their catalog.
On my old DV-22 it seemed like water always sublimated very quickly below 1200 microns and much slower above 1200 regardless of the temperature. If I held a solid reading below 1,000 I was satisfied my system was tight, dry and free of non-condensibles.
I've probably said it before on this thread, but any reading below 250/300 with oil in the system is BS ... refrigeration oils boil in that range. You can't get below that range with liquid boiling in the system.
On the other hand, do not confuse oil boiling with refrigerant gas leaving solution with oil ... its like CO2 leaving soda ... the water isn't boiling, the CO2 is just leaving the solution. Tapping a compressor to accelerate this is the same thing as shaking a soda or beer. DO NOT energize a compressor to do this. In fact, make sure 3 phase compressors with 2 pole contactors are completely disconnected on all 3 legs while in vacuum.
Last edited by boat racer; 08-23-2011 at 08:46 AM.Sam
Know-it-all? Nope, not even half!
08-23-2011, 12:01 PM #114
I've seen the tree, it looks nice. I had a problem with my robinair 15434 blankoff/isolation valve leaking. I called robinair support and they suggested the o-ring repair kit, so I got that and installed it, but still leaking. I also found that I had a leaking tree on the pump, my 5/16 cap was leaking and I didn't know it. But with all those things fixed the 15434 blankoff/isolation still wont below about 700 microns.
I read this tech note on the JB DV-142n on how their blankoff ball valve works so I bought a DV-142n platinum vacuum pump. It does seem to work like they said, shut it off slowly while the pump is still running, and in the pause position it will remove the rest of the air in the valve.
'Information on testing the vacuum pump's isolation valve' on page 2:
"With a micron gauge connected directly to the intake of the pump and vacuumed to 50 microns, closing the isolation valve will result in a rapid rise in pressure, almost to atmosphere. Look closely at the area around the isolation valve. (Figure 14) Even though small, air is trapped in this area. When we begin to close the isolation valve, there is a position of the ball that allows this trapped air to enter the vacuum being created. On a large system, this small amount of air would not create a conspicuous change in microns. However, with almost no volume, the sudden introduction of air to this direct hook-up is obvious and would be displayed on a micron gauge. Refer to the previous page for the isolation valve positions. When the isolation valve is put in the pause position, this gives the cartridge (the pumping mechanism) access to the air trapped in this area and within a few seconds, that trapped air is removed."
So I was going to run the 3/8 hose directly to each of the 3/8 taps on my DV-142n pump, the other ends to core removers, and one of those with a side tap for the micron gauge. Then I should be able to use the DV-142n blankoff to hold the vacuum, unless the vacuum hoses permeate, but if they did then I could still use the ball valves in the core removers to blankoff the system to check for leaks or a rise in the micron gauge.
I'm just wondering if someone has already tried holding the vacuum in the vacuum rated hoses, with a tree or a working blankoff/isolation on the pump.
08-23-2011, 02:01 PM #115Professional Member
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08-23-2011, 08:17 PM #116
is there anything wrong with using a standard flare tee on the vacuum pump?
1/2" flare X 1/2" flare X 1/2" male NPT....
And then valve the vacuum off with the core tools.
Any reason to use a tree?
08-23-2011, 08:34 PM #117
nothin wrong with doin that, some just like the tree because it has valves built in.
i use the jb 142n pump with 2- 3/8" ports and a 1/4" port built in.
i use 3/8" to 1/4" yellow jacket hoses and 2 appion core tools on the service ports.
i dont use a tree, i use the setup that came with the pump, it works just fine, just make sure its leak free.