Rotary vs standard compressors

[mytekcontrols]

Rotarys are no good for 24/7 usage because of the low back pressures we use in computer phase change, running a rotary in vacuum will knacker it within months.

Hmm... I am puzzled as to why this would be the case. If it's due to the poor mass flow at these low suction pressures causing over heating, then I would think that this should also be an issue on a reciprocating as well. Perhaps adding some extended surface to the rotary's outer shell would cure this (I think I remember a post or two that showed wrapping expanded metal screen around the compressor for this very purpose).

Another solution to this problem might be to add a bit of higher boiling refrigerant such as butane or pentane to aid in heat removal (and improved oil return as well).

And if you make autocascades like I do, then this is a non-issue, since it is not necessary to run low suction pressures in order to achieve cold evap temperatures on such a unit.

[Xeon th MG Pony]

Rotarys are no good for 24/7 usage because of the low back pressures we use in computer phase change, running a rotary in vacuum will knacker it within months.

Recips are a better alternative for 24/7 setup, they are mainly low back pressure, but won't reach the temps a rotary can unless it's a massive and noisy lump.

If it's a now and again benching unit you're after, then go rotary, if it's 24/7, go reciprocating

and no i'm not a phase expert, just read it somewhere :p

Never make an authorative statement bassed on some thing you read some where, it leaves you sounding not to bright given the guy who said it possibly wasn't all there hime self!

All ways look into these things. fyi dosn't matter what compressor you use so long as it is kept in its design window.

[mytekcontrols]

Very good post SoddemFX. And it appears we are in agreement on some of the points I made earlier.

Some interesting quotes from your post...

A rotary compressor is no different to a normal compressor, it is just a motor driven device which does work on a gas.

A compressor running at a very low suction pressure will have a low (relative) mass flow because of decreased gas density and reduced volumetric efficiency, this means that the extra power added in compression (from all the inefficiencies) will cause a much greater temperature rise than if the same power was added to a large mass/sec of gas in a system with high mass flow.

A good point about rotary cylinder compressors is that because of the high volumetric efficiency they are able to achieve the required mass flow at very low suction pressures.

All this is ignoring shell heat rejection (which is significant) but I think that would confuse this a bit too much, because for me there is too much guessing about the insides of compressor and the heat transfer inside the compressor case.

Basically it just comes down to good system design, and staying within the recommended parameters for a given compressor. Whether that be a rotary or a reciprocating one.

[boshuter]

Rotarys are no good for 24/7 usage because of the low back pressures we use in computer phase change, running a rotary in vacuum will knacker it within months.

That is simply not true... the rotary build I did a year ago has been running everyday for a minimum of 8 hours with very few days off. It runs the whole time loaded to around 200w and is in or very close to vacuum (and I don't mean it hits peaks of 200w, it runs the whole time under that load just crunching numbers). The guy that owns it has had zero complaints and is asking now about converting it to nehelam. I'm willing to bet it will still be running another year from now. If it isn't, the compressor cost $18 including shipping, I spend more than that on Ceramique in a year.

[sjg0]

I think it's important to note that:

sometimes you can find a freezer/fridge that comes from the factory with a leak and isnt charged at all sitting in there (my case)

So he was actually not venting at all (so he claims).
What i dont think is right is that he is encouraging illegal activities. Which I dont believe is illegal.

So sorry KaptCrunch, but i think the only thing you would be able to report him for is theft.

O btw: That looks like a AWESOME little recovery tank Xenon. I just have 2 questions:
Why would you not pressure test it before vacuuming it out? Is it just assumed that your tap will have no leaks and the tank will be able to hold decent pressures?
And will one of those be able to store all the refrigerant in a typical phase-change system or will I need like 5 to recover all refrigerant from one system?

[teyber]

you are wrong sjgo. it was edited out but it said something along the lines of "open it up go have lunch or something let it empty out and then cut out the compressor" which is illegal.


So sorry KaptCrunch, but i think the only thing you would be able to report him(not report him steven, but advocating it others) is violation of the clean air act

cheers

[sjg0]

So he was actually not venting at all (so he claims).
What i dont think is right is that he is encouraging illegal activities. Which I dont believe is illegal.

you are wrong sjgo. it was edited out but it said something along the lines of "open it up go have lunch or something let it empty out and then cut out the compressor" which is illegal.

So sorry KaptCrunch, but i think the only thing you would be able to report him(not report him steven, but advocating it others) is violation of the clean air act
cheers

Sorry but i dont understand why you think i am wrong. I am aware of the "go have lunch" tidbit, hence why i said: "What i dont think is right is that he is encouraging illegal activities."

Eh, I cant really make out what your trying to say in 2nd sentence (dont blame ya its late)
But unless the constitution of the united states of America just "went away" recently, he is entitled to whats called: "Free Speech"
So it is in fact NOT illegal for him to promote crime.
Here is a fun little example backing up my statement: weed. pot. marijuana.
Are the people protesting legalization committing a crime?
Are the rappers who sing about smoking weed all day committing a crime?
etc...

[ruffus]

@sjgo i have made those small recovery tanks my self as well and they do work good as well yes they should hold all the refrigerant from a single stage as they will hold up to 1 pound @ around 300psi. (i would not go over this pressure) but the one thing you have to do is make sure it is sealed up real good and check the weight on it like once a week or so to make sure you are not loosing any gases as 2 of the tanks i made work good at first then they got a leak over time. OH YOU MUST NEVER TRAVEL WITH THEM REAL BIG NO NO READ THE WARNING ON THE TANK BEFORE YOU TAKE OFF THE LABEL!!!!!!! AS IT IS LAW TO NOT TRAVEL WITH THEM IF RE-FILLED

[sjg0]

Ok. Sweet thanks ruffus. Umm when you say travel does that mean like i cant cross state lines with it or i cant leave my property with it?

[Xeon th MG Pony]

I think it's important to note that:



So he was actually not venting at all (so he claims).
What i dont think is right is that he is encouraging illegal activities. Which I dont believe is illegal.

So sorry KaptCrunch, but i think the only thing you would be able to report him for is theft.

O btw: That looks like a AWESOME little recovery tank Xenon. I just have 2 questions:
Why would you not pressure test it before vacuuming it out? Is it just assumed that your tap will have no leaks and the tank will be able to hold decent pressures?
And will one of those be able to store all the refrigerant in a typical phase-change system or will I need like 5 to recover all refrigerant from one system?

I've been doing fab work since I could walk so I had no doubts it was a solid thread (But to verify I weighed the tanks in timed intervals to ensure nothing poped up. others may need to pressure test and should. One should hold the full charge, but depends on size of system, user common sense comes in here.

[wdrzal]

Ok. Sweet thanks ruffus. Umm when you say travel does that mean like i cant cross state lines with it or i cant leave my property with it?

To even place recovered refrigerant into a tank or vehicle to move it, the tank MUST be D.O.T. (deprartment of transpertation) approved in the USA. And have a non-expired hydo test date. Be carfull buying used tanks,they may be expired.


Never fill a tank more than 80% full. Back to basics: keep in mind refrigerants have different volumes per pound as compared to water.

30 lb DOT recovery cylinders w/Y valve are around $50 to $60 dollars wholesale.

A lot of early recovery machines used tanks with floats (@ higher tank cost/approx + $30 dollars) The trend has been to do away with the more expensive floats and just weigh the tanks.

That brings me to a observation. I never seen a refrigerant scale pictured being used on XS. I'm sure some guys have/use them...........

[teyber]

To even place recovered refrigerant into a tank or vehicle to move it, the tank MUST be D.O.T. (deprartment of transpertation) approved in the USA. And have a non-expired hydo test date. Be carfull buying used tanks,they may be expired.


Never fill a tank more than 80% full. Back to basics: keep in mind refrigerants have different volumes per pound as compared to water.

30 lb DOT recovery cylinders w/Y valve are around $50 to $60 dollars wholesale.

A lot of early recovery machines used tanks with floats (@ higher tank cost/approx + $30 dollars) The trend has been to do away with the more expensive floats and just weigh the tanks.

That brings me to a observation. I never seen a refrigerant scale pictured being used on XS. I'm sure some guys have/use them...........

i use my mom's scale to measure them. Check out littledevil's build thread, hes got an programmable one from refco.

[ultralo1]

. And have a non-expired hydo test date. Be carfull buying used tanks,they may be expired.

If you do find yourself the owner of one with an expired Hydro, call a local dive shop or your local fire dept to find out who does their hydro testing.

[wdrzal]

If you do find yourself the owner of one with an expired Hydro, call a local dive shop or your local fire dept to find out who does their hydro testing.

The tanks are good for 4 years from date of manufacture,then only 1 hydro test good for 4 more years. So a tank has a 8 year service life. I have many tanks that look like new that never left the shop but can't be re-tested.

[sjg0]

The tanks are good for 4 years from date of manufacture,then only 1 hydro test good for 4 more years. So a tank has a 8 year service life. I have many tanks that look like new that never left the shop but can't be re-tested.

Thats pretty weak, if your in a situation like that can you at least trade-in your new but expired tanks for new ones. Or trade in for a 50% discount?

[wdrzal]

Basicly your supposed to scrap them........You need to even watch when buying brand spanking new ones, one time I seen new tanks sold by a wholeseller that where already 18 months old, so that gives you 2.5 + 4 years of use. Thus the warning to check Date of manufacture(which is first factory hydro test) before you buy.

[ultralo1]

The tanks are good for 4 years from date of manufacture,then only 1 hydro test good for 4 more years.

I am not familiar with that could you point me to the laws regarding it?

It maybe one of those things I learned and forgot.

[wdrzal]

I would have to do some searching, been a long time since I took the universal cert. years before it was even mandated to do so.But all the tanks we buy are Amtrol and they have a paper tag right on them stating 4 + 4 years. That falls under the DOT but I took a 40 hour class on recovey in the late 80's iirc and our instructor coverd it. Not sure if all the abreaviated (16 hour) and open book online coures would even cover it.

http://www.amtrol.com/refridrec.htm

for some reason my browser is getting a error opeaning the pdf on recovery tanks,not sure but it may be explained in there also,can't recall.

american company but all their tanks are made in Portugal.

[wdrzal]

Just looked at orginal prep manual and it says hydro test every 5 years,refer to DOT rules. Actually every state could have different DOT rules for transport.

Also says DOT containers must meet federal code of regulations "title 49 ,parts 100 to 177"

[vab206]

ok, 1st im not saying that i ever vented, i didnt. 2nd i was just mentioning this as a last resort. but seeing as you can buy new compressors that have never been ran for ~20$. i aquired mine that way because i wanted to keep my build cheap. i have under $200 in my build and im very proud of what its looking like so far. 3rd, theres no theft involved. reading my post will clarify this, i say go and ask your store manager, but in reality even if someone comes with a dumptruck and loads up everything in that trailer without asking a soul theres actually nothing that can be done. the stuff in that trailer is property of noone once it enters that trailer. lowes simply recycles whatever is in that trailer for environmental purposes. i mention the whole shelf deal because when you try to explain what a phase system is and that your hooking it up to your computer you get some really wierd looks... trust me, especially if your from a southern state.


im pretty sure that hydro tests extend the service life of that tank by 4 years reguardless. now im not 100% on recovery tanks but i know that when i played paintball competitevly i ran into a guy in penn. that had a tank dated from 1988, was 2002 at the time and they were filling it (45cu. in. 4500psi) without any question. i stayed away from him the rest of the time i was there

[dinos22]

i have a rotary in my SS
its LOOOOOOOOOUUUUUUUUUD

[Solarfall]

i have a rotary in my SS
its LOOOOOOOOOUUUUUUUUUD

i have 2 rotarys in my cascade..i'm already getting used to the "loudness".. my neighbors sadly aren't

[dinos22]

i have 2 rotarys in my cascade..i'm already getting used to the "loudness".. my neighbors sadly aren't

ROFL
my little daughter things someone is doing some building work next door with a jackhammer or something "loud" every time i bench with it

[Xeon th MG Pony]

My scuba tank @ 3,000 PSI every 5 years is a hydro and every year is a Ultrasonic fatique test, untill a stress crack is found or it fails hydro/Ultrasonic/Visual it is good!