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Dual Stage

Danielm

Member
Joined
15 Mar 2018
Messages
55
Location
London/essex
So - I have picked up just about enough knowledge to be dangerous. I think I am going down the CO2 route and have leaning away from JBL as some suggestions that while the kit is pretty solid, you are limited to the JBL refills.... having a 250l tank with overflow/sump, I think I need to be planning to have some reasonable size refills.

So I am looking at the CO2Art options, but it is not clear to me what the difference between dual stage or single stage is...i seem to have the option between the Elite and SE series for dual stage, but not sure if the extra price is worth it?

Any advice greatly received!
 
Single stage gives you control until the CO2 turns gaseous, then it can lead to an increase in output pressure and subsequently your Bubbles per second, whereas dual stage gives you complete control regardless of liquid/gas level.
 
Basically, single stage comes with a predefined pressure set up, I believe CO2Art sets the ones they sell for 4 bar, dual stage allows you to play around with it.
 
The regulator contains adjustable membrane/valve (brass or stainles steel plate) retained by a coil spring. Completely closed this spring is strong enough to close the membrane and hold the 50 bar CO² pressure to close it. When you turn the regulator knob, you slowely open the membrane releasing a small amount of CO². The spring gives counter pressure and regulates the gas pressure fluctuations to a minimum. To reach a relative constant outflow pressure.

Now CO² in gas form is extremely temperatur sensitive, the presure rises when temp rises. So with a regulator containing only 1 membrane (Single Stage).
These slight changes also result in a somewhat fluctuating output. But pressurized liquid CO² is rather darn cold and keeps all gas form above it cool enough so this is rather unnoticable. When the bottle is near empty there will be no more fluid CO² in the bottle and there is no more cooling property. It takes on the invironmental temperature from the room the bottle is in and the CO² expands exponentialy for a brief moment resulting in a drastic increasing pressure possibly above 50 bar. The famous tank dump. The single stage membrane spring cannot hold this sudden increasing presure to it's set value and this also increases the output.

To prevent this and make the regulator more reliable a Dual stage / 2 Membrane regulator is designed.

Now the regulator has a Max. output of 20 bar, you cannot set it higher. So it has 1 build in fixed spring retained membrane at Max. 20 bar and behind this a 2nd adjustable spring retained membrane to fine tune bellow 20 bar. Thus in case of a tank dump the adjustable membrane never gets more than 20 bar pressure to reduce.Making it a lot more stable.

That's the nutshell explanation about single and dual stage difference.. 🙂

If it is worth it? Depends on how keen you are on controlling it personaly. Keep an eye on the pressure in the bottle near the time of the bottle end. Be the tank dump a step ahead and replace the bottle on time. This makes you personaly the dual stage prevention. Are you the type that likes to forget about things than a dual stage is worthy investment, your fish will love you for it.

All tho, did read horror scenarios with desent priced modern designed fancy super small hobby grade dual stage regulators forgetting what they were build for and still dumping the tank. It's questionable in how far you should put your trust in technical devices all the way.
 
Now CO² in gas form is extremely temperatur sensitive, the presure rises when temp rises. So with a regulator containing only 1 membrane (Single Stage).
These slight changes also result in a somewhat fluctuating output. But pressurized liquid CO² is rather darn cold and keeps all gas form above it cool enough so this is rather unnoticable. When the bottle is near empty there will be no more fluid CO² in the bottle and there is no more cooling property. It takes on the invironmental temperature from the room the bottle is in and the CO² expands exponentialy for a brief moment resulting in a drastic increasing pressure possibly above 50 bar. The famous tank dump. The single stage membrane spring cannot hold this sudden increasing presure to it's set value and this also increases the output.
Nothing to do with cooling at all. The CO2 is liquid at room temperature AND a pressure of 55bar. As an aside liquid CO2 does not exist at normal atmospheric pressure, only gas and solid.

A single stage regulator "with a membrane", as you say, will keep fine regulation provided the tank still contains liquid CO2 at 55bar pressure. No problems there. What does happen when the liquid runs out and only gas is left the tank pressure starts to drop and the output pressure also drops. My single stage regulator starts loosing its 2.6bar output pressure when tank pressure drops below 30bar odd. Generally in quality single stage regulators as the tank empties the output pressure just drops, no dumping, just your CO2 injection rate drops as output pressure drops. With my 2Kg fire extinguisher and single stage regulator this takes 3-4 days after tank pressure starts dropping before CO2 injection bubble rate drops. Normally enough time for me to notice and change the tank. If I leave mine CO2 injection rate just slowly drops to zero as tank empties. No issue.

With a dual stage regulator on regulator reduces the pressure to say 14bar and a second stage, usually adjustable as well, reduces this 14bar to say 3bar. Because of the dual stages the output pressure does not vary (too much) when the tank starts to empty, the output pressure stays constant until the tank pressure reaches 14bar, where it then all stops. Some people like this as it gives another CO2 knob to fiddle (output pressure) and you won't have algae & plant problems due to carrying CO2 levels as tank empties. However the downside is, you will get no in tank notification CO2 is running out ie reduced bubble rate, as the CO2 will just stop when tank is empty. This is a problem/difficulty if you locate you CO2 in a cupboard where you cannot easily observe the tank pressure gauge easily/daily.

However there are a third class of cheaper regulators that are not really regulators but flow control valves that produce reduced pressure ie 3bar from 55bar tank pressure by using a pin hole or metal sponge to restrict gas flow. These work fine, but suffer from the issue of complete loss of regulation when tank pressure starts to fall and can vent the remaining tank contents. This is brilliant if you are CO2 welding, you get a rush of gas, disrupting your weld which tells you to change CO2 cylinder. In a fish tanks this emptying of gas is probably fine if you are using a 14gr or 95gr disposable canister, the end of tank dump is not much gas, no problem. However if you are using a 2Kg cylinder the end of tank dump can be a considerable quantity of gas, this asphyxiating all your fish.

So dual stage is nice, if you can afford it, but single stage is also ok.
 
Thanks @ian_m i stand corrected (again). I thought to remeber something in my nutshell that wasn't there.. Had to look it up again.. Remebering the -72°C of expanding CO² (dry ice) got me on the wrong foot mixing things up..
 
Here is graph of CO2 vs pressure with my lines added. At 55atmospheres (bar) and 20'C the CO2 is liquid, as in a fire extinguisher. At 1 atmosphere solid CO2 turns to gas (sublimes) at -78.5'C.
upload_2018-3-27_12-28-51.png
 
Before going the CO2 route find a dependable source for CO2 first, otherwise it becomes a hassle.

Great point - luckily I think a few of the delivery options cover either me or my parents house, so supply should not be an issue !
 
thanks for the detailed responses guys. Will have a better read later, but I think for the extra £40/50, the dual approach gives me all the upside, with no downsides.
 
Hi ,
I have the co2 art pro se dual stage (my first decent regulator) it was simple and easy to set up with a 2kg fe i got off amazon uk.....
Cannot recommend enough....it also has a solenoid hooked up to a cheap wilko time switch. Once you figure out on off period in conjunction with your lights it’s virtually maint free except for bottle changes. I am a novice to injection but was surprised how easy it is after the pain of paying out for some decent kit...
Cheers
Chris
 
Danielm I see your location as London/Essex. Thameside in Basildon refill a 2 kgFE for a fiver. Look them up on the web. I just go round the back and they are refilled in 5 mins. All properly checked for leeks etc.
 
Danielm I see your location as London/Essex. Thameside in Basildon refill a 2 kgFE for a fiver. Look them up on the web. I just go round the back and they are refilled in 5 mins. All properly checked for leeks etc.

Thanks Alan. Planning a trip to summerhill over the weekend so will look them up.
 
Only a few mins from summer hill. The sat nav doesn't get it quite right. Its on the westward bound side of the carriage way. It's a reasonable sized place with a big sign! I have been up and down the road a few times! No idea if they are open weekends.
 
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