What is for you the ideal procedure or what procedure do you use to vacuum a system?
Does someone have a pressure/temperature chart of water for the vacuum range?
What is the phormula to calculate the relation between P and T?
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What is for you the ideal procedure or what procedure do you use to vacuum a system?
Does someone have a pressure/temperature chart of water for the vacuum range?
What is the phormula to calculate the relation between P and T?
It depends on what you are trying to get out of the system, Peter. At its simplest just getting non condensables out of new pipework is straightforward if you are sure that no air has got in. If this is the case there may be minute quantities of moisture entrained. (Some fitter think nothing of removing seals from rolls of pipe that have been in their vehicles over night in the winter in a warm environment).
If on the other hand there is serious moisture or water in a system (flooded chiller for example) be prepared for a long siege. There are certain techniques, but it?s a job that can take weeks.
When I was on the tools, many years ago, clearing out centrifs after split tubes was a speciality. I would seriously talk to the insurance loss adjuster first in case he wanted to scrap the kit. The reason is that not only were you in for a re-tube of the effected parts, but a complete mechanical strip-down, re-oil followed by an extensive dehydration of the unishell when they were reassembled. On old R11 units, the purge would take small amounts of water out, but it was easily overwhelmed.
In dehydration, one thing is certain. You must keep the temperature of the units as high as possible in order to maximise the vacuum pumps efficiency and to avoid crystallisation (ice). This involved controlling the depth of vacuum. Invariably no two jobs were the same and it?s not something you can walk away from. Not only the unit but the vacuum pump. On large jobs I would have arranged an array of at least four or six pumps. Even then the job could take weeks before I was sure it was dry. This is why I used to give the loss adjuster the option of scrapping the kit once he knew what the costs were likely to be.
How do you know when it?s dry? I used to have a wet-bulb hygrometer in a glass tube that was installed in the vacuum and left for about half an hour. Nil moisture is exactly the same as on a Psychrometric chart. I don?t know where it is, but I can still remember how to make one.
If I remember correctly, Carrier had a chiller manual on the subject. But that was in the 70?s??.
To answer your last question, the best vacuum steam table in my opinion for this kind of work is an absorption equilibrium chart. Unfortunately most of them come from American manufacturers and are in Imperial units, but you can read off pressure against temperature quite easily. Carrier or Trane should have them on their web sites.
Hope this helps
________
herbal store
Hi Peter,
Well i would like to say that i am completly professional and use a vacuum gauge at the farthest point of the system to the vac pump, but probably like most engineers i do not own one.
Usual procudure, on a fairly small system is to pressure test with ofn to make sure there are no leaks. Blow the Nitogeon, vac out (time depending on size), break vac with OFN and then re-vac.
I know i should use a micron guage but even if i had one it's been so like since i done a thermo king course i can't even remember what micron level you should get below.
Regards
Fatboy
A good quality torr gauge such as an Edwards fitted with a pump isolation valve is an invaluable piece of equipment to use while "vaccing out" and it will also tell you much about the system that you are working on, personally I vacc everything down to 1 mbar, if it wont pull......you have a problem! (but check gauge lines and manifold first)
Hi...further to the vacuum posting...all in the firm I work for are issued with an electronic vacuum gauge which can be switched between various scales...Torr....Microns...Hg...etc....also to cope with the problem of wrecking vacuum pumps when dehydrating a system where a shell and tube has failed(You can change the pump oil as much as you want but a severely flooded system will still tend to wreck your pumps as you cant stand with them all day)we use a series of ice traps which we design and build ourselves (although the technology is well known I dont believe there are any commercial versions available....I may be wrong??...let me know)...if anyone would like a sketch of how to knock one of these units together together with connection diagrams let me know.....they are simple to make and will save you money if you deal with dehydrating large chiller failures due to water contamination.Best regards all....
PS....If anyone wants me to email them a copy of a steam table...also let me know??
I am new to this forum and am finding it very interesting.
I did serve my time as a refrigeration engineer and have been in the trade ever since. I am 'hands on' more than 'technical'.
I've never had the time or the patience to study the subject properly. I admire those who do.
As for evacuating I was tought to triple vac the system (after first pressure testing for as long as possible with OFN). We use electronic vacuum guages. I was taught that the colder the ambient temperature, the lower the vacuum is required to boil off the moisture. I was told 5 TORR was low enough whatever the temperature (and it gets pretty cold in Scotland I can assure you). Shut the gauge and switch off vac pump and see if it holds a good 5 minutes. If it does you are in business.
I have found that cutting corners on this task is asking for trouble. Moisture is the enemy.
I hope that I understood the question correctly and I also hope that my procedures are correct.
One last thing; look after your vacuum guage, they are like women, very delicate and expensive.
PIST :D
Welcome PistonBroke and ...an original name.
If you go lower then the values as stated in the table below, then normally, all the moisture should be gone out of the system.
How long do you hold this vacuum?
Ice in a system -mositure in the evaporator in a freezer - can also be removed if you go long enough under 1.12 Torr.
Any comments on this?
How do you control the vacuum level in the system?
Have some of you used the Supco VG64 for this?
I have to admit, we pull vacuum as long as we can, mostly 24 hours, attach a simple dial vacuum meter to it and pump as long as possible (time is money). After some days, we then only switch the dryer on larger systems and that's it.
On smaller systems like 1 HP, we mostly install an oversized dryer like a 163 type or a 303 on a freezer.
°C Torr mBar Pa
-18 1.12 1.5 150
0 4.6 6,13 613
5 6.5 8,66 866
10 9.2 12,26 1226
15 12.8 17,06 1706
16 13.6 18,13 1813
17 14.5 19,33 1933
18 15.5 20,66 2066
19 16.5 21,99 2199
20 17.5 23,33 2333
21 18.7 24,93 2493
22 19.8 29,39 2639
23 21.1 28,13 2813
24 22.4 29,86 2986
25 23.8 31,73 3173
30 31.8 42,39 4239
PS: it wasn't possible to manage the table so that it looked nice. Sorry
hi Peter
You see, you are just getting too technical.
It makes my brain hurt and I have to go to the pub.
Cheers
PIST :D
I'm allways eager to learn Superheatman.Quote:
Originally Posted by Superheatman
I would guess that I cant teach you very much Peter...you could probably teach me!!....I will draw a sketch of the ice trap setup and forward it to you...could you drop me an email to jonathon287@msn.com so that I have an email address to send it to....it might be a few days as I am up to my neck as we all are with the recent hot weather...did you want a copy of a steam table as well??...best regards...John (Superheatman)Quote:
Originally Posted by Peter_1
Peter, GO here http://www.hyvac.com/Products/Filt_T...Ice%20Trap.htm
They are quite useful when evacuating a wet system as they protect the integrity of the vacuum pump and oil. They also help lower the system vapor pressure. Some people use liquid nitrogen, I used dry ice as its readily avialable.
Thanks Wambat and others.
But what I'm specially interested in is how you all do your normal vacuum procedure in the field.
How long do you vacuum, till what pressure, do you control it with electronics, do you brake the vacuum with gas and re-vacuum it, do you use own rules for puming time according to the size of the system, how often do you change the oil,, do you use the gas ballast valve on your pump( if there is one), on stage or tow tage pump, ....
Hi peter,
When changing a comp on a small system like a chest freezer or upright chiller, I always vac the system for as long as it takes to make a cup of tea and have a smoke. :) :) :)
As I would only be vaccing air out the system I don`t see that any longer is required. Moisture.... well thats a different story, It would be vacced for as long as I had time for.
When making repairs to an existing system I follow the following procedures
I use silver/phosphorus/copper alloy with between 5% and 15% silver, and when I braze on most repairs and use nitrogen flowing through the lines to eliminate carbon deposit buildup on the inside of the joints because of the contamination On small systems I will remove the Schrader valve cores and connect the nitrogen bottle to one valve and set pressure regulator to about 2 psi. After brazing I visually inspect the quality of the joints (a mirror helps), then reinstall the Schrader valve cores and pressurize with between 125 to 150 psi of dry nitrogen and check for leaks.
Then I will connect my manifold pressure gauges, micron gauge, and vacuum pump. And release the nitrogen charge and begin evacuation. For faster evacuation, I will use minimum 3/8” hoses and I leave the gas ballast valve open on the 2-stage pump until I reach 1000 microns, then I close it. On larger chillers I will use ½” flexible steel braded hoses and as short a possible or about 3 feet
I will evacuate the system to 300 microns or lower with a micron gauge and 2-stage vacuum pump. This could take about 30 minutes for a system that is not contaminated. However for a contaminated system such as a burn or a tube rupture I will use a cold trap with 300-watt heat lamps and do a triple evacuation, eventually I will valve off and turn off the vacuum pump and wait for at least 20 minutes to make sure the micron gauge reading does not go back up above 700 microns. If it does, I will re-start the vacuum pump and evacuate for another 30 minutes. I will repeat this process until it is successful, assuring that there are no leaks and all moisture and non-condensable particles are removed. I had a large capacity solenoid valve on the suction line of the vacuum pump wired so if I lost power, the solenoid would close to prevent any vacuum pump oil from contaminating the system.
Quote:
Originally Posted by wambat
Hi Wambat....sort of what we use but ours have their own condensing unit and evaporator can so that we can leave them running for days if neccessary....the problem with the illustrated one is that you have to keep replacing the dry ice or whatever in the shell which defeats the object in my opinion....ok if you are going to stand with the pump set for a few weeks I suppose??..also on large systems we do a standing vacuum test at least overnight(depending on the size of the system)...sometimes even several days ...better to find problems before introducing the refrigerant charge...it takes a long time to recover several hundred Kg of refrigerant if a leak becomes apparant later..best regards.
Wow, I like your equipment, when I first started with my first service truck it was so bad that if if I loaded the back end with too much equipment the front end would lift the wheels up and i would lose control for a few seconds unless I slowed down and for tools they issued me a rock, string, and a stick :rolleyes: :D
Quote:
Originally Posted by wambat
I hope that your rock and stick were fully covered by the current safety regulations and that your string had an insurance test certificate :) :) :)
5 Torr is no where near enough vacuum...The minimum you should acheive is .5 torr or 500 microns..you should always evacuate below 500 microns (.5torr) then if it rises above that after 15 mins...not 5..then evacuate again. The rate of rise will also tell you whether you still have moisture in the system. If it rises at a steady rate then there is probably a leak in the system. If it rises faster in the beginning then slows down..then there is still moisture presentQuote:
Originally Posted by piston broke
If you can't get to 500 microns or below..then change the vacuum pump oil.
Thanks Deejay, I shall adjust my working procedures accordingly.
We are very thorough in all areas, by keeping pipes clean using OFN when brazing and pressure testing. The vac does usually go below 5 TORR. We are also working mainly on higher temperature equipment like air conditioning. We never get any moisture problems if we have installed and commisioned the system but thats no reason to get complacent.
Thanks to all who have posted info on evacuation procedures including Peter (I was only pulling your leg). All good advice is much appreciated.
Have a good weekend.
PIST :D