Finishing refrigerant recovery

G'day all,

In the spirit of the recent question on ensuring your manifold and hoses are as empty as possible before disconnecting, I have a question that has been puzzling me.

I now have a recovery unit. When I recover a system and purge the machine at the end, there always remains a significant quantity of liquid in the hose between the machine and the recovery cylinder.

The only way I've been able to get reasonable results is by finishing up with a cylinder cooling cycle to chill the cylinder _way_ below ambient, and heat the hose up. I still lose quite a bit of vapor, but no liquid this way.

What is the correct way of minimising refrigerant loss at the end of a recovery?

when recovering refrigerant you should not really be left with a large amount of liquid in your line between the recovery unit and the recovery cylinder.
are you purging your recovery unit correctly?
i am assuming you are recovering all the refrigerant from the system?

http://www.javac.com.au/docs/support...nual_evoos.pdf

you will find recovery procedures here.

Right, and that is how I'm doing it.

Let me walk through my understanding of how the recovery process works and see if you can spot what I'm missing.

- The recovery machine draws refrigerant from the source unit. It compresses it, condenses it and pipes the condensed refrigerant as a liquid (mostly) into the recovery cylinders liquid port.
- When you switch the valves on the machine to purge, it routes the condenser and associated pipework to the input side of the machine and connects the output of the compressor directly to the outlet pumping any refrigerant in the unit directly out the output port without passing through the condenser (hot discharge vapor).

At the end of the purge process, the output gauge on the machine is still reading the cylinder pressure, however the mass refrigerant flow is negligible.

Thinking it through, it would appear that as the hot gas flow tapers off, the hose relatively quickly cools to ambient temperature (which is cooler than the cylinder) and liquid refrigerant migrates back up the hose (or the hot gas condenses in the hose).

Does this sound feasible ? It would certainly be consistent with my experience of preventing it by chilling the cylinder prior to purging the machine.

I wonder if a check valve at the tank end would stop this occurring ?

the questions im asking im not trying to insult your inteligence BradC

when your carrying out the removal of refrigerant from the system correctly be it standard removal and also you can use the push pull method on sytems with over 5 kg charge with a liquid receiver as im sure your aware.
obviously ensuring you have no trapped liquid refrigerant in the system.
you say your cooling the recovery cylinder prior to purging by throttling the discharge port from the recovery unit.

when your purging the recovery unit are you ensuring your are pulling a suitable vacuum on the inlet gauge on the recovery unit.?
i understand what your saying reference the liquid migration etc i understand where your coming from but if the system is purged correctly then you shouldn't really be getting this problem.
there no harm in fitting a none return in the line from the recovery unit outlet to the recovery cylinder or even fitting a sight glass.
what ever precautions you can take in order to reduce the chance of emmissions the better.

Hi Brad
I'm not sure if it would be legal to fit a non return valve in the line as it could be considered a drain from condenser to receiver. The best way I have found to eliminate almost all venting of refrigerant is using lines with ball valves on each end, this way the lines hold refrigerant until the next process. The only time this does not work is if you use different refrigerants. The most common in ac is R22 and some blends or mixes use r22.
I find having a valve at each end of the hose very helpful - for checking vacuum, isolation or simply swapping hoses around.
I don't use schrouder valve depressor inserts, I use quick couplers instead as the inserts slow dramatically process flow. I also use schrouder valve removal tools for pressure testing and evacuation.
I have noted most other techs and suppliers do not have hoses with valves but they can be bought separately or on the net (much cheaper).
Another method is to use that last bit of gas from the reclaim unit for trace gas if a nitro leak test is to be performed. I went through the course and obtained the ARCTICK license recently where they expect we keep refrigerant in the gauge lines, there are several small problems with this being if we use different refrigerants often and what if we had a line full of liquid on a cool day and they heated up to over 50degC. But have the valves almost eliminates purging or venting of gasses. The cost of refrigerant is getting very expensive where it used to be used to blow out the odd condenser, flush systems, freezing shafts and certainly not recovered, crap we even used to purge systems of air whilst charging. Today it would cost more not to recover/reuse refrigerant. I share one reclaim unit with ten other techs on a fixed site:
The only way to comply is to measure and record every process of refrigerant use. I saying we should write down what the reclaim was last used for, how much was reclaimed, when and if it was dirty or clean. This recording of process should also be done on bottles and the system it's self.

@ cold.man, yes I run the recovery unit until the vac gauge is pegged during the purge process. I still end up with liquid in the discharge line.

@ Tesla, where did you do your Arctick license? I've been trying to get some training and accreditation and have been told in no uncertain terms that unless I'm willing to toss in my career and do a 4 year apprenticeship as a fridgy there is no way I'll ever get licensed. Bit harsh I thought, and certainly not really doable as a 37 year old with a mortgage and family. I'm willing to spend thousands in training to migrate my career if I can, but I can't afford to go back to apprentice wages to start from scratch. One apprenticeship was enough!

Nice tip on the hoses with valves. I'm due some new hoses anyway. I've got screw in valves on the end of my hoses now, but they all leak slowly.

I'm not fussed really about blowing off refrigerant, as not being licensed I'm doing all my experimenting with HC's, but in the quest to learn and obtain a license I'm trying to get the correct procedures down.

I completed an apprenticeship many moons ago and just had to catch up on my licenses with a local tafe course and assessment/test for level 3 refrig & ac, then proficiency cert then ARCTICK - a lot of work.
For some quality hoses & valves etc check out yellow jacket on ebay to give you an idea of what I use.
You should be fussed about "blowing off refrigerant" literary, as it is well legislated in this country these days. I'm sure you could do some parts of the course - if not through the net by post to help you understand how to best handle refrigerant and all the little tit bits.

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Originally Posted by Tesla

You should be fussed about "blowing off refrigerant" literary, as it is well legislated in this country these days.

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Remembering I'm not licensed, when I refer to refrigerant in the context of "blowing off", I'm referring to a dried commonly available hydrocarbon gas. It's not "refrigerant" as legislated by Arctick as it contains no flourine. It's also cheap and easy to get and thus a great learning tool :)

Sorry brad
Just meant to startle you a little as +99% of the time forum members use controlled refrigerants. As for the other gases like the HC you are using can still be dangerous like flamable. It's great to see you giving it a go which makes my and others replies worthwhile.
My problem at the moment is getting all these gauge valves for R410a as it uses 5/16" flare size where all the rest which I have is 1/4" flare. I feel the local suppliers are not stocking enough of the right stuff so I will buy of the net and wait for a month or two weeks. Mean time I must borrow fittings from other techs for this gas. Keep up the work and experimenting.

Thanks for the reply.

All the literature I've found on recovery systems and processes state you need to hook the recovery machine up to the liquid line on the cylinder. Having thought through my issue above, I wonder if I'd be better off hooking it up to the vapor port, that way there is no direct link between the liquid and the hose. Might have to give that a crack..

I see the 410A stuff seems to be using different fittings. What a pain in the backside. The local guys just don't have a decent selection of much really. I generally get most of my oddball gear from overseas. I bought my testo 550 here though as I wanted the warranty support!

Yes most definately hook up to the vapor line on cylinder, this ensures there is a drain from the condenser (reclaim unit) to the reciever (bottle).
I find it takes a little longer but some purchases are saving more than 50% from buying on the net.

use an extra vacuumed bottle and release the liquid from the recovering machine into it.

I've done it in the preparation towards the F-Gas exams at least 500 times and I have seen it already more than 1000 times during exams. Is this question still valid?
A hose full of liquid contains +/- 25 gr refrigerant. We weighted this already.
Recover via the vapor side unless you use the push-pull method.
When you've recovered, your bottle temperature will always be slightly above ambient. You always have a certain DT above ambient and you never can condense the refrigerant in your unit to ambient.
So pressure will always a little bit higher. So pressure in the hose will be slightly above equivalent pressure of the 'ambient pressure'
Second, the last step was recovering without the inner condenser, direct from recovery compressor o bottle, so second reason why pressure will be higher.
You only have to wait some time (5 to 10 minutes) to let your bottle cool down to ambient so that bottle pressure reduces so that you will have a flow towards your bottle and refrigerant will migrate to the bottle.
Try also to install your unit higher then your bottle so that you have a flow downwards along you as short as possible hose.
We show that you can recover with +/- 20 gr loss on a filling of +/- 2000 gr.
Installing an NRV isn't allowed nor needed, same for ball valves. What will you do when you recovered R134a and your next machine is a R404a one?
But the valves are usefully, p.e. when removing the hoses from a compressor with no SV where you have to remove those with no loss at all, according to the Belgium F-Gas. If we hear a sissing sound when removing the hoses from a small hermetic compressor, then we have a reason for failing the test. Try once to imagine how you could remove your hoses from the service valves on the receiver and suction without an SV in the system!

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Originally Posted by Peter_1

I've done it in the preparation towards the F-Gas exams at least 500 times and I have seen it already more than 1000 times during exams. Is this question still valid?

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I asked the question because I did not know the answer, so it's valid to *me* anyway. By asking the question I was hoping (and I succeeded) to obtain input from those more experienced than I. Aside from blowing things up and making mistakes, it's how I learn!

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Originally Posted by Peter_1

You only have to wait some time (5 to 10 minutes) to let your bottle cool down to ambient so that bottle pressure reduces so that you will have a flow towards your bottle and refrigerant will migrate to the bottle.=

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Thanks, this did the trick nicely. I "recovered" from one bottle to another as a test, and after shutdown went and had breakfast. By the time I'd returned there was no liquid at all in the hose.

I know I tend to ask what appear to be silly questions, mainly because I don't have a mentor to teach me this stuff. I'm learning as I go in the hope of one day migrating my career.

These were no silly questions at all. I see that 95% of the technicians doesn't know how to perform this rather simple task. As so many times, it's so easy once you know how to do it the proper way.

I charged a blast freezer today with 5 ton of R422d (pigs) (bombs) what we call them. outside at 2 degrees , I probably lost about a kilo or 2 with purging from drum to drum etc, thats 2000 grams does that mean I am deliberately venting? I think not.

The standards and legislation need to look at the industry as a whole not just the smaller end (charge amount)
They also need to police the trade if they want any results.
I could legitimately name (which I obviously will not) at least 500 folk/companies who are working without any registration or certification

I do not think my 2 Kg will be a problem

Rant over long day

Quality, I agree that there's a difference between theory and practice. But as always, standards are made by clerks behind their desks at 24°C whom can't make the difference between a water pump and a compressor and by some lobby groups who wants to make the standards as stringent as possible. And then all the school and exams centers sitting there in these meetings...oh boy. Real craftsmen don't have the time to sit in these meetings to make these standards more workable for us, the technicians in the field, standards adapted to the real life, not something coming out of the books or methods used 30 years ago.
I sat in the F-gas commission in Belgium, preparing the Belgium standards and I know what I'm talking about.

I sat on the first exam in the UK and thought it was under what the industry needed but I have no control

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Originally Posted by Quality

I sat on the first exam in the UK and thought it was under what the industry needed but I have no control

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I was on the second course and got 100% so it must be way too easy!!!

Went outside for a break while they were marking the papers and no one told me i'd passed, sat there for hours watching the pile of papers stack up, the longer it went on the more i thought i'd failed :D