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Degradation of Airline tubing


  1. CO2 setup
    by George Booth <> (Tue, 16 Jan 1996)
  2. CO2 tubing
    by krandall/ (Mon, 03 Aug 1998)
  3. Check Valves for CO2
    by "James Purchase" <jpurch/> (Tue, 26 Sep 2000)
  4. (No Title)
    by ()
  5. Check Valves for CO2
    by "Neal, Cathy" <Cathy.Neal/> (Tue, 26 Sep 2000)
  6. Check Valves for CO2
    by Dan Dixon <dandixon/> (Tue, 26 Sep 2000)

CO2 setup

by George Booth <>
Date: Tue, 16 Jan 1996

> The airline tubing that came with the system is a black rubber. Is
> this a special tubing to handle co2? I'd like to get a longer piece,
> but I'm not sure what to use.

Here's some info from an old posting:

| Newsgroups: rec.aquaria
| From: (Jerry Cullingford)
| Subject: Re: CO2 regulators and solenoids ?
| Date: Mon, 21 Feb 1994 15:41:43 GMT
| (Dana Merrill) writes:
| >Hose: $1.90 from aquarium shop.  I am using ordinary vinyl hose.
| >Supposedly vinyl hose is not appropriate CO2 but the only silicon
| >tubing they had at the shop was blue; I didn't want blue.  I have
| >heard from several people that they have been using vinyl for years
| >with no problems.
| According to Dennerle, who sell aquarium C02 systems, silicon hose is
| actually far worse than PVC:
| C02 losses per metre of hose, against 0.3 metre water head:
| (g = grams, not gallons!)
|                       Daily   Monthly   Yearly        Factor
| Dennerle CO-Proof     -       < 1g      approx 10g    1
| 4/6mm pvc hose        0.197g  6g        72g           7
| silicon hose          2.95g   89g       1076g         100

Perhaps you have Neoprene hose.  I think that would be black.  I don't
know how it comapares with the above types.

CO2 tubing

by krandall/
Date: Mon, 03 Aug 1998

Neil wrote:

>I have "been told" that conventional air hose is not good for CO2 because
>it will diffuse out.  Supposedly, not true for silicone and some other
>materials. Vinyl also gets brittle with age and this 'may' affect the
>diffusion. Comments or references? 
>Even if true, I now wonder about speed of the diffusion. Maybe it is of no
>practical significance for aquarium applications unless the length of
>tubing is high and the gas residence time is long. For example, if there is
>a 1 percent exchange in 1 hour, we would not care.  

I don't know any exact figures for diffusion, but Claus seemed to think
that for short distance runs, it would not be much of a problem.  If you're
piping it through several different rooms, you might lose more CO2 than you
wanted to pay for.

As far as vinyl becoming brittle is concerned, I just went and checked the
tubing of my first CO2 system, which has been running without interruption
for over 5 years.  The tubing is till very flexible, with no sign of
cracking, discoloration or deterioration.  I think I paid less than $1 for
the length I needed, so I think I got my money's worth, even if it _did_
fail at this point.<g>

Karen Randall
Aquatic Gardeners Association

Check Valves for CO2

by "James Purchase" <jpurch/>
Date: Tue, 26 Sep 2000

One little piece of equipment which is usually included in CO2 systems is a
Check Valve. Some manufacturers of CO2 equipment for aquariums either make a
separate one (Dupla, Dennerle) or encorporate it into things like Bubble
Counters (Dupla) or CO2 Diffusors (Dupla, Eheim).

I suppose that they are concerned about water from an aquarium getting
sucked backwards and into things like Needle/Regulating Valves and/or
Regulators. I just don't know how "secure" these little bits of plastic
truly are, and when considering a set-up that might contain several hundreds
of dollars worth of valves and regulators, I'd like to make sure that my
investment is protected from water damage.

The APD archives and the KRIB contain scant information on Check Valves.
There are numerous posts regarding the failure of cheap valves, probably not
compatible with CO2.

When I look at my Dupla Check Valves, I notice that they are plastic bodied
and are "spring-loaded" internally. They are described by Dupla as "Type
4.5", with no explanation of what this means. Anyone know? They are rated
for a Maximum Pressure of 3.0 bar (44.1 psig), which I assume means that
they should never be exposed to anything higher than this. The Minimum
Pressure is listed as 0.15 bar (2.2 psig) and I assume that they mean that
below this level they will close, preventing flow in either direction. Am I
thinking correctly here?

When I look at various valve manufacturer's web sites, I can see that there
are lots of folks making Check Valves. Most of the manufacturers give a bit
more info than Dupla does, and in different formats.

For example, Swagelok makes several different series of Check Valves, and
they list properties such as Working Pressure, Nominal Spring Size, Cracking
Pressure and Reseal Pressure. Swagelok defines Cracking Pressure as the
pressure at which the first indication of flow occurs and Reseal Pressure as
the pressure at which there is no indication of flow. I'm stumped as to
figure out what an "appropriate" figures for these things would be for an
aquarium situation.

Working  Nominal   Cracking  Reseal
Pressure Spring    Pressure  Pressure
psi      Size psi  psi       psi
C Series
3000     1/3       Up to 3   6 back pressure
3000     1         Up to 4   6 back pressure
3000     10        7-15      3 back pressure
3000     25        20-30     17 back pressure
CH Series
6000     1/3       0-3       6 back pressure
6000     1         0-4       5 back pressure
6000     5         3-9       1
6000     25        20-30     17

Since the two most common ways of feeding CO2 into an aquarium (sintered
ceramic disk, requiring 10-20 psig for optimal use, and a reactor requiring
only 1-2 psig) I'm wondering how ONE type of check Valve can be used for

Why do some valves with really low cracking pressure require higher reseal
pressures than other valves with higher cracking pressure?

What kind of "back pressure" is generated within a CO2 line when the
positive flow of CO2 is cut off upstream of the Check Valve?

How do you select a Check Valve to suit our needs from looking at the
Cracking Pressure and Reseal Pressure values? Which combo would work for
aquarium applications?

(No Title)


If someone can provide some insight here, I'd appreciate it (and I can think
of a few others on the list who would as well).


James Purchase

Check Valves for CO2

by "Neal, Cathy" <Cathy.Neal/>
Date: Tue, 26 Sep 2000

Hi all,

James, I noticed that you did not mention anything about ADA's line of glass
check valves. ADA makes a check valve called the Cabochan Ruby. This
hand-blown glass check valve contain a small red glass bead to prevent back
flow. Would a glass check valve work better than plastic one? I would think
so. Since CO2 can cause some plastics to become brittle glass would seem
like a better choice. But of course we can not buy this North America, but
hopefully this won't be for long.


Check Valves for CO2

by Dan Dixon <dandixon/>
Date: Tue, 26 Sep 2000

James Purchase at wrote:

> One little piece of equipment which is usually included in CO2 systems is a
> Check Valve. Some manufacturers of CO2 equipment...

[interesting check valve information snipped]

> If someone can provide some insight here, I'd appreciate it (and I can think
> of a few others on the list who would as well).

I just use a coil of tubing above the water line. The coil prevents water
from siphoning in the event CO2 pressure is suddenly lost for some reason.
No back pressure problems, and it's very inexpensive. Not recommended for
DIY yeast systems, though.

Dan Dixon

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