"DANGERS" of a Cascade System ????

[runmc]

Several people here at Xtreme, including myself, have decided to build ( or acquire ) Cascade Systems.

I for one don't want to get injured, and I surely don't want my daughter or wife hurt by an explosion inside my house.

Can you guys who have experience with, and knowledge of Cascade Systems, PLEASE give us noob warnings on what happens to cause a dangerous situation with a Cascade. Can you also give us safeguards on how to prevent dangerous situations.

We have all been warned of how dangerous a Cascade can be. Please give us the do's and don'ts

Pics of safty devices or cascade sytems with safety devices and links to safety devices would help everyone out alot

Thanks guys, Ron

[ellsworth]

one thing that i will be doing on my setup is, i currently bought 2 omega temperature controllers that will monitor temperatures of both stages, and if one temperature goes out of bounds then the controller will shut down the whole system with a relay. another thing is to have a relief tank on the low stage, and plenty of other safety measures such as solenoid valves and othr misc failsafes. i think the temperature controller idea is a good one, i just got 2 omega temperature controllers for cheap on ebay.

[]JR[]

Charge the lowstage when off, to a safe 'off' pressure, this is one of tha kaboom failures, too much high pressure refrigerant and not enough volume makes for not a happy puppy.

Also another kaboom is the high stage failing/not performing efficently with the lowside on, so need high side performance monitor.

Safety feature is a solenoid to open the high side and low stage pressures together in the lowstage, over pressure opens to lots of volume.

Oil seperator for the lowstage, possibly small % hydrocarbon refrigerant to assist oil transport.

]JR[

[DaBit]

JR said most of it. My safety scheme is based on high pressure cutout on the low stage and temperature control on the interstage HX. And be sure to vapour-charge the thing when off. I'd say that you should go no higher than 8 bar / 120psi static pressure on the low stage.

[Tom Holck]

Originally posted by runmc
Several people here at Xtreme, including myself, have decided to build Cascade Systems.

I for one don't want to get injured, and I surely don't want my daughter or wife hurt by an explosion inside my house.

Can you guys who have experience with, and knowledge of Cascade Systems, PLEASE give us noob warnings on what happens to cause a dangerous situation with a Cascade. Can you also give us safeguards on how to prevent dangerous situations.

We have all been warned of how dangerous a Cascade can be. Please give us the do's and don'ts

Ethan (R170) -80 -90 C and Ethen (R1150) -100 -120 C are explosive gas.
I have done some test, and will late this year have a system working!!
I don't dare to mes with that myselfs, so I have a proffessionel company doing it.
They work with cascadesystems all day. The explosive power of 10 grams is the same as if you throw a lighter in your fireplace!!
20-30 grams can sure do some serius damage "under the table" if you are sitting there, and the PC explode.
My costummade cascade will have a stanless steel cover, that can take an explosion -nothing will happend- but a destroyid PC

It's very relevant Ron, thank for bringing it up

[herefishy]

Hmmmmm. I've been looking over some of the characteristics of my R13. It appears that @ -114F @ 0psig, the R-13 is twice as dense as say R-502 @ -50F, 0psig.

I'm thinking that in the case of accomplishing the same amount of work as say the TPA1410 applications (R-404A), that a compressor rated @ the 2,100 btuh cpacity @ -10F for the application should employed for the second stage (in the case of the R-13 application) - twice the nominal rated capacity.

I would think that the 1410 however, would be appropriate for the first stage with perhaps R-134A @ -10F in order to maintain about a 192psig head pressure on the R-13 system.

NO, NO, NO,... I've got it. I would employ two low-temp R-404A compressors @ the 1,050 buth nominal capacity -10F, and employ the R-13 in the second stage, and the R-404A in the first... that sounds about right.

[Gary Lloyd]

Let's imagine that you have a refrigerant container with both liquid and vapor in it. This is called a "saturated" mixture.

If you warm the container, some of the liquid will change to vapor. The pressure will rise along with the temperature. This can be seen on a saturated pressure/temperature chart for the refrigerant. If you know the temperature, you know the pressure. If you know the pressure, you know the temperature.

As you continue to add heat, the temperature and pressure increase in lock step, and there is progressively more vapor and less liquid. This continues until there is only vapor in the container (the mixture is no longer saturated). At this point, if you continue to add heat, the pressure will not rise.

Very high pressure refrigerants must never be saturated at room temperature, because the pressures would be extremely dangerous.

The cascade low stage is charged with vapor only, at room temperature and reasonable pressure, and with the system turned off. Liquid is only present when that vapor is reduced to a very low temperature. If you charge it with the system running, as you would a conventional system, when it warms up to room temperature (system off) it can go...

KAAAAABOOOOOM...

[chilly1]

You need a weak point built into the system.... I weaken a piece of tubing (using a tubing cutter) so it will rupture at a known point in a controlled manner. (on the liquid line) and use due care in assembling your system. Use high quality brazing alloys 15% silfos or simmilar. Make sure all devices are rated for the pressures of the refrigerant you are using. A pressure relief device rated at 800 psi another option.

[]JR[]

Thats a nice idea, although i dont think theyres going to be a lot of 'control' about it, although you could enclose it in box which will stop bits flying but let the gas out...

]JR[

[captaincascade]

use high pressure switches set to 300 psi.


BOOM!

good luck, id think youd wanna start off building 4 or five singles first. JUST DONT DO IT ALL IF YOU HAVE TO QUESTION SAFETY.


"hey Bill, you think i should go skydiving"?
"of course, im not doin it, but what could go wrong. yeah go ahead"?

[fr0st]

Originally posted by Gary Lloyd

As you continue to add heat, the temperature and pressure increase in lock step, and there is progressively more vapor and less liquid. This continues until there is only vapor in the container (the mixture is no longer saturated). At this point, if you continue to add heat, the pressure will not rise.

Since temperature is a measure of kinetic energy, heating a gas to a higher temperature will results in the particals moving faster. The faster they move the more they hit the edges of the container.
Everytime they hit they exert a force, namely pressure.
It's Boyles or Charles law, I can't remember

[runmc]

Originally posted by captaincascade
use high pressure switches set to 300 psi.


BOOM!

good luck, id think youd wanna start off building 4 or five singles first. JUST DONT DO IT ALL IF YOU HAVE TO QUESTION SAFETY.


"hey Bill, you think i should go skydiving"?
"of course, im not doin it, but what could go wrong. yeah go ahead"?

hey captain,

nice to meet you..

BTW - I appreciate your -humm- concern.. Mark Willett (herefishy) will be putting my cascade together for me. I am merely trying to get a thread going that can help benefit everyone. Noob in general.. This thread is to promote safety!!

All constuctive comments are welcome.

[captaincascade]

i think my posts might be being read wrong. if i spoke my posts in person they wouldnt be taken the wrong way. I'll try not to post with my somewhat condasending sense of humor, and my young-bachleor Los angeles dialect.


The most important and simple safety measure, The high pressure switch

[DaBit]

Originally posted by chilly1
You need a weak point built into the system.... I weaken a piece of tubing (using a tubing cutter) so it will rupture at a known point in a controlled manner. (on the liquid line)

I doubt you are able to weaken a spot 'just enough' yourself. The weakest points are the various large diameter pressure vessels such as the oil sep and the compressor. I doubt you can easily reduce the strength of an 1/4" or 3/8" pipe so it will rupture before the compressor does.

To solve this: use commercial overload protectors; they are designed for this.

A pressure relief device rated at 800 psi another option.

800psi?
Am I invited at your funeral?

Never forget:
- Safety devices can fail too. Account for that.
- Electronics and every device with software inside is unreliable.
- Physical laws cannot be beaten, so use that for safety.

[Charles Wirth]

Chilly1 advice is not for the noob, its for someone who knows from experiance.

He built my cascade and I know its 100% safe at all times. I know how to treat it and respect the dangers when I shut down.

It is kept in a secure area where no one can bump it or even get near it other than myself.

My best advice is if you have kids under 18 in the house, do not even consider having one in your house.

Other advice would be not to leave wires exposed, discharging a large start cap into yourself in not fun.

[runmc]

Thanks guys

It's getting better all the time!! If you can think of anything, it will help.

What are the Dangers

Where they occure, what causes them

How can they be prevented

Thanks for going over these points already, I'm just updating the thread.

No thoughts are too small or insignificant, please share them..

I've listened to the refrigeration experts we enjoy on these forums and I know this is something way over my head. We can all learn together..

[DaBit]

Originally posted by FUGGER
Chilly1 advice is not for the noob, its for someone who knows from experiance.

If my compressor says on the warning label that it's max low side pressure is 225 psi, I am certainly not going to set a safety to 800 psi. If fact, none of the hermetic pots we use is designed for 250+ psi low side pressure.

He built my cascade and I know its 100% safe at all times. I know how to treat it and respect the dangers when I shut down.

With my cascade I can just flip a switch to turn it on or off.

It is kept in a secure area where no one can bump it or even get near it other than myself.

If someone bumps mine, the only danger consists of a VERY angry DaBit.

My best advice is if you have kids under 18 in the house, do not even consider having one in your house.

When finished, mine is dangerous in only one respect: the -72C cold head. Touching that is not healty.

Fugger, I do not doubt the capabilities of your refrigeration engineer (yours works, mine is limited by the R410A), but when I hear you speaking about 'respecting the dangers when I shut down', 'keeping it in a secure area' and earlier 'using a UPS to keep the high stage running in case of power failure', I do *not* consider it a school example of a well built and safe system.

Damn man, use that high pressure switch. Use those cheap temp controllers to sequence the compressors. Take advantage of the physical laws to limit pressures and dangers involved with pressures. It takes at most half a day to incorporate all that. And if you can afford the R508b, you can also afford the <$100 needed for all this safety stuff (HP switch, tempcontrollers, expansion tank).

I have once breathed chlorine gas. I have once had the glass of my safety goggles almost shattered when a drill bit broke. I have once set my trousers on fire with a angled disc cutter. I have seen the damage caused by a ruptured oxygen bottle.

I learned my lessons the hard way. Why should you if I can tell you all that?

[chilly1]

http://www.henrytech.com
P/N 5230N - 735
Part number for valve for 735-2000 psi pressure relief valve

R410 can get to 800 psig under the wrong conditions I have seen 410 operating at 550 psig condensing (dirty coil, jumpered high limit,120F and one Techlooking for a job) . If we are talking of a relief device we are not talking of operating pressures we are talking of burst pressure or the pressure at which the parts of a system will fail. If you have a relief device set below the burst pressure, sized according to the internal volume of the system and built of materials for the refrigerant in use then no worries. R508b which I have in Fuggers system is at 600+ psig at 85F we here in Las Vegas can have ambient temperatures of 120F+
So 800 psig is probably conserative, However, I usually size the system components of the low temp side so that I will have almost no liquid that is not disolved in the oil. Oil capacity is also increased by 16 oz. This lowers the chances of catastrophic failure. The burst of 1/4 inch soft copper tubing in my system is 2000psia. I've had my guages on a 40 hp screw compressor when the check valve failed closed. the burst of my guages was 1500 psi my hoses burst, before the compressor shut down.
When we were first testing this system we ran the high temp side for a few minuets to minimize the risks until we had a baseline on it. Currently the static pressure of the low side is 450-600 psig when off. Under high load the condensing pressure of the low side is 175-200 psig. (this is the 508 side) the 507 side is 225-245 psig

[CodeRed]

those static pressures are enough to scare me off a cascade system

wouldnt a relief tank help there?

[Gary Lloyd]

When we were first testing this system we ran the high temp side for a few minuets to minimize the risks until we had a baseline on it. Currently the static pressure of the low side is 450-600 psig when off. Under high load the condensing pressure of the low side is 175-200 psig. (this is the 508 side) the 507 side is 225-245 psig

What you have here is a system that is extremely dangerous, and unnecessarily so. There is no reason to have that kind of static pressure. There just simply is not enough internal volume for the charge. I would start with an evaluation of the low stage cap tube sizing. At design load, if the difference between low stage SCT and high stage SST is more than 15F, then the cap tube can be shortened, thus reducing the R508b refrigerant charge. If the internal volume is then insufficient for the charge, an expansion tank should be added. There is no way I would allow that system to remain as is.

[Charles Wirth]

Gary, no cap tube.

One sweet week at comdex, running 24/7

I had gooch touch the compressor before I shut it down and it was barely above ambient.

I shut it down and promply moved it out of Comdex.

Im home and already back up and running.

[DaBit]

Originally posted by chilly1
R410 can get to 800 psig under the wrong conditions I have seen 410 operating at 550 psig condensing (dirty coil, jumpered high limit,120F and one Techlooking for a job) .

My system does not contain liquid when off.

If we are talking of a relief device we are not talking of operating pressures we are talking of burst pressure or the pressure at which the parts of a system will fail.

Burst pressure should be 4-5x max working pressure. The relief device should be set just above max operating pressure.

R508b which I have in Fuggers system is at 600+ psig at 85F we here in Las Vegas can have ambient temperatures of 120F+
So 800 psig is probably conserative,

No, it's not. These are crazy pressures. The two weakest points in your system:
- The compressor shell
- The oil separator

The compressor shell has a burst rating quite close to that 800psi. The oil sep can take a bit more.

The burst of 1/4 inch soft copper tubing in my system is 2000psia.

That doesn't say anything. The burst of any captube is even higher. Large diameter things are the weakest, not the small diameter things.

[runmc]

Originally posted by FUGGER
Gary, no cap tube.

One sweet week at comdex, running 24/7

I had gooch touch the compressor before I shut it down and it was barely above ambient.

I shut it down and promply moved it out of Comdex.

Im home and already back up and running.

Fugger could you please explain what Comdex means?? I'm lost!!

[Charles Wirth]

Comdex is a yearly expo here in Las Vegas where anything to do with computers are show in exhibitions. I was in Abit's booth.

this year so only an estimated 60,000 people showed up.

CES is next and thats comsumer electronics show. thats much larger and has the adult portion as well the AVN awards the same week.

www.comdex.com

[Gary Lloyd]

Gary, no cap tube.

What metering device are you using?