Cascade 2nd stage pressures

[SexyMF]

Eventually I am going to build a cascade rig. Looking at people who use C02 or R1150 as 2nd stage gases, how do you cope with the static pressures when the system is off. I am meaning, if I'm reading the gas data correctly, at a moderate ambient temperature of 25-30C the pressures are tens of bar.
I realise this is why building a casacade is dangerous.

What does normal soft copper (as used by many) handle?
Do you use higher pressure hoses/guages. The working pressure of most are lower than the gases at 25C ambient.


I have access to R23. I could do a R290/R23 casacade. It would not yeild awesome temps but I'm more concerned about pressures at the moment.

Cheers

[wdrzal]

Different sizes/diameters ..........different wall thicknesses matter M,L,or K then you guys mostly use soft but their is hard.

pressure affect area you need to memorize from 1/4" to 2" in all copper wall thicknesses

you also need to understand how pressure affects area.

All for you to research and memorize. you will learn other important things along the way, go buy or go to the library to read some books that give edited accurate info, I can't take a 1000 page book and condense it into a few paragraphs.

You need to do some formal study(reading A Book or ten) on your own.

If you want to mess with this stuff you need to understand how it work and the physics why its works and what never to do so you stay safe.

[runmc]

Some where around ten bars (150psi) is a round number for static. You run over that easy with a single stage.

If you have a strong cold first stage you shouldn't see any higher pressures than a single stage

Your problems start when the first stage cr+ps out. :eek:

[SexyMF]

You need to do some formal study(reading A Book or ten) on your own.

I'm asking in terms of thoses who have done it. Did you use 800PSI gauges etc. Did you use soft are hard copper etc etc


If you have a strong cold first stage you shouldn't see any higher pressures than a single stage

I'm not talking about running pressures. I'm talking about when the system is off and the second stage gas returns to an ambient temperatures like 25C.
There can easily be over 30bar.

[wdrzal]

what if first stage fails second stage needs to contain pressure, a relief valve should be used on second stage.

R23 is used as a first stage refrigerant in cold parts of the world at room temp its a second stage gas.


800 psi is double the maximum psig you should be playing with ............you should have no more than a 450 psi relief valve. and that can kill you if you have a catastrofic rupture in a home made part, compressor cans can stand that beyond that you need to read up on tubing ,I'll point you in the right direction if you want to learn but I not designing systems or you won't learn much,you don't learn by copying what others have done either..many of you guys take pressure way too lightly. also the chemical engery in flammable refrigerants and the oil in the compressor.


Ever hear about the electrical pins flying out, then you have whats called "electrical pin ejection with ingnition"

[{.bLanK} GoD]

Ever hear about the electrical pins flying out, then you have whats called "electrical pin ejection with ingnition"

Yes. I read here not so long ago someone had that experience. The pin went through a solid block wall. :eek:

I am also planning on building a cascade at some stage.
But I'm in no hurry to build a time bomb.
I will research till the cows come home. And only when I am 100% happy I know what I'm doing, Then it will be time to make some freakin cold stuff. :D

[n00b 0f l337]

Releifs are a must as Wdrzal says, and the main thing is your static pressure with the first stage not running can be very high. A high pressure cutoff is needed, and can also make sure you dont turn on the 2nd stage by accident, while a expansion tank can help lower your pressures. But does anyone have a source of larger expansion tanks that are cascade sized?

[wdrzal]

Remember the larger the area the thicker the walls must be to withstand high pressure

[blind_ripper]

hi .
here are 2 pics off cascade with R1150 , fully shut down for 1day ;)
http://i3.photobucket.com/albums/y90/blind_ripper/DSC00216.jpg
http://i3.photobucket.com/albums/y90/blind_ripper/DSC00219.jpg
dont know if its build with soft or hard copper thouge .
hope u can do something with the pics :)

[Moc]

Hm, you don't charge a second stage with a lot refrigeriant so static pressure is not really high. With R1150 it will be @ around 13-17bar...
If you have a big highpressure side you need a expansion tank on the low pressure side.

[SexyMF]

@wdrzal

Look I appreciate your safety woes but you are way off track here.
I am not some rookie about to charge a homemade cascade system with several kilograms of gas which will result in potentially lethal pressures at room temperature.

If you must know, I am qualified to work on (and do, every day) single phase and three phase power systems. I have a safety head on me. If I did not, I would have been electrocuted long ago. There is more risk in all the unqualified people here who wire up mains, than the possibility of explosions or something bursting resulting in projectiles. Not to mention those who onsell these rigs, possibly to other countries.



-----

I am asking these questions to gain a better understanding from people who have built these systems. Such answers do not readily present themselves in text books. Especially for the low wattage, low volume systems used to cool computers.

It is obviously quite possible to make cascades because it has been done. And from the threads I have read, no special anything was used. I don't consider safety cutoffs as special. The last chiller I built used an overpressure switch which ties into a circuit I made. The chiller is unsupervised 24/7 use so if something goes wrong it shuts off and stays off.

I have been reading about and learning about phase-change for the better part of 3 years now. I am no teenager who wants a super-cooled computer just for leet bragging rights.


So, all in all, I would some answers and input to minor questions I'm asking. I won't let this degrade into a 'safety is paramount' , 'go get a phase-change degree before proceeding' thread. I'm not asking for a hand-holding walkthrough.


Thank you blind_ripper and Moc. I like pictures and revisit them often.

So how can you calculate the pressure vs the amount of charge?

[Brettbeck]

I have the 1st stage done on my cascade and static pressure is around 5-6bar (with r290/r404a). When I finish the 2nd stage and charge it (either with co2 or 1150), I will expect the static charge to be similar but probably a bit higher. This is with my garage warmed up to 30c+. I had ambient temperature up to 36c the other day and pressures didn't really change much.

[wdrzal]

As I said before almost all my post are directed toward all members,just because I make a statement in your thread you don't have to be so defensive, I have no idea of your work or age or knowdledge,you brought up 800psi, so I gave a apropreate wanning.because you understand electricity does not mean you or others understand pressure and pressure vessels. separate fields. a cut off is not enough if a blockage is what cause the pressure to rise ,it will keep rising ,shutting off the compressor is not enough to prevent failure,release of pressure is last resort,but required to be safe. I feel anyone mixing gases or building cascades should use cut offs ans relief valves.

I continue to try to gets guys to build the correct safe way,the same as you would do for new guys working with you and the way you install electrical components,by the book.Here in the USA its the NEC(national electric code)

these systems are simple single stage or cascades only difference is evaporators are smaller and compressors are push beyond design specifacations.

290/R23 is a great first cascade ,be sure to use a relief valve.r23 is not as available in warm climates as its relatively high pressure.

I do agree that a lot miss the electrical part of refrigeration. and the related dangers of electricity it self or bursting capacitors full of hot oil.

I design and install single and 3 phase industrial and commercial power systems also,along with residential all have different requirements and voltages.even do up to class 2 hot work,when needed 17,000 volts as you know.The local power company tests my safety equipment before ever time I do class 2 hot-work,or at least monthly for gloves and sleeves I usually sub it out to a Friend but sometimes hes not available. I prefer to disconnect,but can't do in all cases of industrial or commercial.

Big A/C or refrigeration sort of goes with big electrical demands ,I install a lot of 400 amp 3 phase services. or multiply drops.

[runmc]

I'm not talking about running pressures. I'm talking about when the system is off and the second stage gas returns to an ambient temperatures like 25C.
There can easily be over 30bar.

If you will reread my first post I said that - "Some where around ten bars (150psi) is a round number for static." (as walt pointed out - "depending on second stage gas" - I was speaking of ethylene)

If you think a cascade second stage is static charged to 30bar (430psi) :stick: "WRONG"

Maybe I'm misunderstanding what your saying.

I think it would be safe to say that a static charge on cascade second stage (@ 25c -77f ambient) would be between 100 -200 psi ( that is ballpark figure) I know some of the guys here have had lower than 100psi static charge.

You may find wdrzal's suggestion offensive, but he's knows way more than many of us here. ;)

[wdrzal]

What does normal soft copper (as used by many) handle?


Being a electriction you know how many amps #12 gage copper wire or 500mcm aluminium can handle?, is that any different than knowing how much pressure different sizes tube can handle when working with tube instead of wire to work safely?

my goal here at XS is not to give single answers because I know you need to know so much more to build safe cascades. Giving single answer after single answer all I'll be doing is giving you a small portion of what you need to know , I want you guys to learn all phases of mechanicals in a building,since I hope you all own your own home someday and then you can do repairs yourself, but since this is a pc site I try to limit to refrigeration and the electricals that go with it.

Just as knowing the above 2 answers does not make someone a electrician,there is much much more to know so you don't kill yourself.

you sure would not draw 1000 amps @ 120v thru 500 mcm,would you,get my point

as I just mentioned in another thread also to memorize the pressure each size of copper can handle.

[sacha35]

Being a electriction you know how many amps #12 gage copper wire or 500mcm aluminium can handle?, is that any different than knowing how much pressure different sizes tube can handle when working with tube instead of wire to work safely?

my goal here at XS is not to give single answers because I know you need to know so much more to build safe cascades. Giving single answer after single answer all I'll be doing is giving you a small portion of what you need to know , I want you guys to learn all phases of mechanicals in a building,since I hope you all own your own home someday and then you can do repairs yourself, but since this is a pc site I try to limit to refrigeration and the electricals that go with it.

Just as knowing the above 2 answers does not make someone a electrician,there is much much more to know so you don't kill yourself.

you sure would not draw 1000 amps @ 120v thru 500 mcm,would you,get my point

as I just mentioned in another thread also to memorize the pressure each size of copper can handle.


As wdrzal said, I am an electrical engineer and safety has to be the first point of call with the electrical wiring and gas insulation setup, I see far to often hear that most units are just put together to see who can get the best temperatures without any concern for there’s or others heath or safety, high pressures and electricity can kill so come on guys start building units with this in mind.