Visitors since May 06

 This is a Robot Wars / Battlebots  inspired collection of information from around the web... an aid to understanding the use of CO2
  in powering pneumatics...but the info contained here is also of help in unrelated areas LOOK around ( it's a bit of a mish mash ).
 There's info on CO2 ...Filling bottles... Bottle Pressure...Cylinder valve threads ... Flow coefficients ... Valve flow... Valves... BSP Threads etc.
New in  pneumatics section ...HERE          A very handy conversion utility...  Download it ..... you will not be disappointed!

 Questions ......Comments .......  EMAIL!

LUXFER  Bottle / Cylinder Manufacturer --HERE   Extinguishers ,Paintball, etc ....   

CATALINA  Cylinders  U.S of A  
HERE   all types and sizes of bottle / cylinder.         1Kg and 2Kg Fire Extinguishers HERE

Cylinder Hire service HERE ....... pick " Dispense"  option.                          Medical cylinder sizes HERE  Sizes C thru to J

                                 CO2 CYLINDER VALVES 

                                                                         You'll find the bottle neck thread size by following the Luxfer and Catalina links above ...
                                                             But normally they're M25 X 2mm ...Older
U.K. bottles 3/4" BSP... U.S. of A  7/8"UNF and 1.125"UNF
                                                                          You can purchase a hand wheel valve to replace the std fire extinguisher squeeze valve from :-

European M25 X 2mm pitch only.                                  
                                                                         Co2 Screw Down Valve (Tapered thread 3/4" BSP )

                           CYLINDER VALVE  THREADS

                                   gas thread Throughout the world, carbon dioxide cylinder valves have a special thread. In Europe, Africa and much of Australasia, the thread conforms to British Standard 341 Part 1 (.860 in x 1/14 in W) or the direct European equivalent (DIN 477, SN 219505, etc). These threads are in effect interchangeable.

        British  BS341  No. 8      European  DIN 477  No. 6   and    SN 219505  Type 7     
                French     NF E 29-650 Type C     Australian   AS2473 Type 30

America CGA 320 and Japanese JIS B 8246 CO2 threads are different and are not compatible with each other nor with British/European CO2 threads).





                     American     CO2 Valve Thread Size                                                        
                                                   CGA 320

      Standard cylinder valve outlet connection for pressures up to 3,000 psig for compressed co2.

                            Cylinder valve outlet thread: .825-14NGO-RH-EXT

        Note:-   Want to use  your U.S. Regulator on a European bottle?...Simply unscrew the stem and replace the nut.
        A  regulator nut  to fit the European thread  can be obtained from  part no:- DACO2NUT

1/2" BSP = CGA 320 ....
Well it is the same apart from the thread angle.
         A female 1/2" BSP .... British Standard Pipe.....  fitting will screw nicely onto the male CGA 320  thread.        

     Paintball Valve



 Inlet  Thread  :  5/8-18UNF

 Outlet Thread  :  CGA 320


       CGA 320 Thread

  Explanation of the above.....

      0.825"  outside dia
     14 Teeth Per Inch
      RH  Right Hand
      EXT External
    NGO... Acronym  for
     National Gas Outlet

             Both Paintball and Soda Stream valves have this special  thread specifically for CO2 called a CGA320 thread.
          CGA stands for Compressed Gas Association...... and is often called an ASA thread or Air Source Adaptor.

          SodaStream adaptors  @  Australia ...type "sodastream" in search for other options
                                                          Sodastream to Paintball adaptor  from Palmer Pursuit.

                                          SODA CLUB CYLINDER

                                                                                SODA CLUB website                    

             The NEW Soda Stream ........or Soda Club cylinder has a strange thread ..... 4.4 mm pitch trapezoidal!     

                                                It's possible to buy this adapter / adaptor
in the USA  HERE  and HERE
                                                                             and Europe HERE

Problems re-filling your  Soda Club bottle? .....This may well be the result of Soda Clubs special valve.
                                                                   More  info at this  blog

     Australia seems to have retained the original SodaStream thread on their new Alco jet bottles
                                         see pic below ......perhaps other countries have as well.


                                             1kg and 2kg Fire Extinguishers also by Soda Club

           Gas Outlet Valve Threads.... designations and dimension

    BSP NPT & Others Screw Threads.     

                                                   How to fill an empty bottle


   This is the process used to refill empty or partially full tanks. Using what is normally called a Fill Station, the tank to be filled is connected
    to the larger storage tank. Air or C02 is then transferred from the storage tank into your bottle.
    For the transfer of air or C02 to take place, the tank you are filling from must be at a higher pressure than the one you are trying to fill.
   Standard CO2 cylinders all have liquid in them as long as they are filled but come in two types. Gas and Siphon.
   Gas cylinders stand upright and releases gas from the evaporation liquid when the valve is opened - this type of cylinder must be turned
   upside down in order to obtain liquid CO2 to refill any cylinder.

   Siphon cylinders have a tube from the valve to the bottom of the cylinder so that when the valve is opened liquid CO2 comes out without
   having to invert the bottle.

   Fire extinguishers are of the Siphon type and Pub Beer Gas Cylinders are of the Gas type.


  The measurement of gas in a tank is dependent on the type of gas. C02 under high pressure is LIQUID the
   fill is always calculated by weight,  never by pressure.

   The weight of gas/liquid  that the bottle should hold will be stamped on the bottle....NEVER exceed it.
   A 2 kg tank is designed to carry safely a maximum of 2 kg of liquid C02.



   A pressure gauge on a C02 bottle can never tell you how full it is.
   The pressure in the tank is connected to the temperature of the C02....Find out by how here
   Air, on the other hand, is measured as a pressure within a fixed volume, the volume of the tank is irrelevant to the pressure you
   can fill it to and the maximum fill pressure is always its safe working pressure, printed on the bottle.


      W.P. = working pressure (or fill pressure). This is the maximum any bottle should be filled to and should be printed on the bottle.
      This will be around 750 p.s.i. as a norm for CO2..........but can rise considerably on a hot day.
     T.P. = test pressure. The pressure the bottle is hydrostatically tested too.
     You should never try to fill to this pressure. Any burst disks must fail before this pressure.

     B.P. = burst pressure… Pressure at which the cylinder will rupture.
    This is prevented from happening by a small thin copper disc retained under a plug in the valve called a rupture or burst disc,
     this will blow @ around 2,200 psi venting the contents of the cylinder to atmosphere. 


    You can fill an empty Fire Extinguisher Bottle in almost the same way. A slightly different order of valves being turned on and
    off is employed. 

   Connect pipe work - making sure dump tap is off - open valve on Fire Extinguisher - open valve on donor bottle - wait while
   the bottle fills , you should hear the gas going in and can guess-timate when the bottle stops filling  -
shut both - vent excess
   in the pipe by opening dump valve - remove Fire Extinguisher and weigh it.

                                                  TEST DATE STAMPED ON THEM.

                            Filling kit and "How to" links on another site........ and


                                                       Properties of Carbon Dioxide or CO2


Molecular weight 44

Melting point -56.6C

Boiling point -78.5(s)C

Critical temperature 30C

Relative density, gas 1.52 (air=1)

Relative density, liquid 1.03 (water=1)

Vapour Pressure 20C 57.3 bar


          Technical explanation of the volume of gas in 1kg of liquid CO2

                   Suppose you have a 1kg capacity fire extinguisher.
                   That is 1kg of liquid CO2
                   The weight of a mole of CO2 is 44g so you know that you have 22.7 moles of gas.
                   At 1.0 atm pressure and room temperature of 298 K, the concentration of an ideal gas is 0.041 mol/L.
                  So at room temp and pressure those 22.7 moles will occupy 22.7/0.041= 553 liters .


           Therefore ....1 kg of liquid co2 will give you approximately :- 

            36 litre's of gas at 15 bar / 225 p.s.i  ,  55 litre's at 10 bar / 150 p.s.i.  and  81 litre's at 100 p.s.i

                                           Online calculator & info for everything CO2 HERE

A quick conversion for our American friends ....... 1lb of liquid CO2 contains 10.3 moles of gas  .......1 mole of gas is 0.86 cubic feet .........So our 1lb of  liquid will expand to a volume of around 8.8 cubic feet or 15,000 cubic inches @ room temp and pressure.

           Temperature and percentage of fill greatly affects the pressure of co2 in
              your bottle (around 750-850 p.s.i. is the norm). See the graph below.
Readings on the red line shows the pressure change with temperature for a correctly filled bottle.
               @ 100 degrees F the pressure in full bottle will have risen to 1400 psi ... @ 120 degrees F it's approaching 2000 psi  .


                                                 Bottle Freezing

If one simply tries to exploit the gaseous phase existing in the vapor space of the tank for process purposes, what will happen is that the gas phase inventory may be depleted faster than tank liquid can vaporize and replace the gas removed.  The amount of heat required to continuously vaporize liquid CO2 is such that external, ambient heat cannot be transmitted through the tank walls fast enough to makeup for the gas removed. This results in a decrease of tank vapor space pressure – sometimes down to very low pressures that approach 5 barg. At this very low pressure, the corresponding saturated temperature of the tank’s liquid would be approaching -56.4oC and all the liquid will be solid
 i.e. Dry Ice. 

The way that the vapor pressure in the tank is kept constant while saturated vapor is withdrawn from the top of the tank is that a liquid vaporizer is employed to generate and replace the withdrawn vapors. The vaporization is usually effected by the use of an immersed electric heater that responds to the action of a simple pressure switch or transmitter that is mounted on the top of the tank. When the pressure decays, the electric heater is activated; when the design pressure is reached, the heater is shut off.

                                                                         CO2 Phase Diagram.......... above.

The carbon dioxide phase diagram has 3 phases -- gaseous, liquid, and solid. The triple point (pressure 5.1 atm., temperature - 56.4C) is defined as the temperature and pressure where three phases (gas, liquid and solid) can exist simultaneously in thermodynamic equilibrium. Above the critical point (pressure 73 atm., temperature 31.1C ) the liquid and gas phase cannot exist as separate phases. This region, known as the superfluid or supercritical phase, has properties indistinguishable from the liquid and gas phases.

At temperatures below −78 C, carbon dioxide condenses into a white solid called dry ice. Liquid carbon dioxide forms only at pressures above 5.1 atm; at atmospheric pressure, it passes directly between the gaseous and solid phases in a process called sublimation.

Enthalpy has a lot to answer for and is the cause of freezing.

With a gas fed source as the pressure drops in an orifice, liquid droplets nucleate and the percentage of liquid increases. At the interface between the liquid-gas and gas-solid regions (near 80 psi.), all the liquid converts to solid - yielding about 6 % dry ice. With a liquid fed source  as the pressure drops in the orifice, gas bubbles form and the percentage of gas increases until the gas-solid boundary is met. Here, the remaining liquid is transformed into solid - yielding about 45% dry ice.

So.......If you use compressed co2 in liquid form and utilise the gas that boils off from it  ...then your containing vessel , bottle or cylinder will get cold .....if you exceed the ability of the bottle or cylinder to warm back up by absorbing heat from it's surroundings then the pressure will drop and the contents may freeze.

A small amount of  dry ice or snow can be formed by the gas as it exits the system to a lower pressure and a large amount of dry ice if its liquid exiting to a lower pressure.

The formation of large amounts of dry ice is to be avoided as this can cause a system blockage.

Fire extinguishers do not have this freezing problem .......liquid is ejected to atmosphere so most of the heat/cold transfer happens outside the bottle.


   When it comes to using pneumatics the following applies.
    Flow = Speed
    Pressure = Power
    A combination of the 2 gives an effective flipper.

   So.....MAXIMISE  your possible flow  ....
   NO restrictions in your pipe work .....
   and a decent size buffer tank  of around twice your rams volume .
   ( The buffer tank contains a " head " of gas @ your required pressure.)

    Several factors have an impact on the flow coefficient.

o      Orifice size (diameter of the piping or opening through the valve)

o      Length of piping or opening through the valve

o      Turbulence caused by bends or turns in the piping

o      Restrictions, or anything that reduces the orifice size or the flow path

o      Shape of the orifice 

                           Flow Coefficient Cv and Flow Factor Kv

 The difference between the flow coefficient Cv and the flow factor Kv.

      The flow coefficient - C v - and the flow factor - Kv - are commonly used for specifying the capacities of control valves.  

    The Flow Coefficient - C v

      It is often convenient to express the capacities and flow characteristics of control valves in terms of the

Flow Coefficient - Cv

      The flow coefficient - C v - is based on the imperial units system and is defined as:

The flow of water through a valve at 60 o F in US gallon/minute at a pressure drop of 1 lb/in 2

       The flow coefficient is commonly used in the U.S. 

      The Flow Factor - K v

       The metric equivalent of the flow coefficient - Cv - is based on the SI-system and is called the

 Flow Factor - Kv

       The flow factor is defined as

 The flow of water through a valve at 20 o C in cubic meters per hour with a pressure drop of 1 kg/cm 2 (1 bar)

       The flow factor is commonly used outside U.S. 

      What is the Qn Value?

        Qn value is used in pneumatics to define the flow of a valve. It is defined as:

        The volume flow in litres per minute of air at a temperature of 20 celcius, with an input pressure of 6 bar and a pressure drop across the valve of 1 bar.

      Converting between Flow Factor Kv  ,  Flow  Coefficient  Cv and Qn

        The dimensions of Kv values can be transposed by means of following factors:


        Here's a list of definitions & Acronym's pertaining to valves....

"100% Area" (Full Port) - means the area through the valve is equal to or greater than the area of standard pipe.

"Standard Opening"
- means that the area through the valve is less than the area of standard pipe, and therefore these valves should be used only where restriction of flow is unimportant.

"Round Port" - means that the valve has a full round opening through the plug and body, of the same size and area as standard pipe.

- Water, oil, gas (Cold working pressure)

"SWP" - Steam Working Pressure

"ANSI" - American National Standards Institute

- Cold Working Pressure


                                                        Ball valve flow

Note :- Kv quoted in litres/min



                                                                              Cv Flow Through Orifices

 0.00001  0.0008"
 0.00003  0.0012"
 0.000053  0.0016"
 0.000090  0.0020"
 0.00012  0.0024"
 0.00017  0.0028"
 0.00022  0.0031"
 0.00028  0.0035"
 0.00035  0.0040"
 0.00061  0.0050"
 0.00086  0.0060"
 0.00120  0.0070"
 0.00150  0.0080"
 0.00190  0.0090"
 0.013  0.0240"
 0.0025  0.0100"
 0.0028  0.0110"
 0.0034  0.0120"
 0.0038  0.0130"
 0.0043  0.0140"
 0.0050  0.0150"
 0.0055  0.0160"
 0.0067  0.0170"
 0.0073  0.0180"
 0.0080  0.0190"
 0.0088  0.0200"
 0.0096  0.0210"
 0.011  0.0220"
 0.012  0.0230"
 0.014  0.0250"
 0.020  0.030"
 0.028  0.035"
 0.036  0.040"
 0.041  0.043"
 0.048  0.047"
 0.059  0.052"
 0.081  0.060"
 0.088  0.063"
 0.100  0.067"
 0.110  0.070"
 0.120  0.073"
 0.140  0.079"
 0.150  0.081"
 0.250  0.100"
 0.500  0.140"
 1.00  0.200"
 2.00  0.270"
 3.00  0.340"
 4.00  0.390"
 5.00  0.440"
 6.00  0.480"
 7.00  0.520"
 8.00  0.560"
 9.00  0.580"
 10.00  0.610"
 20.00  0.875"
 25.00  0.975"
 30.00  1.075"

             Approx flow rates for servo assisted 2/2 valves.
Info also applies to 5/2 and 3/2 spool valves.

      Note that the flow for these is almost 1/3 that of the equivalent size ball valve.
Or if you like your pipe or tube could flow nearly 3 times more.


                 PACulatorValve sizing and flow calculator

       The answer to your valve flow questions       ....       CLICK ON THE ABOVE LINK      ...       remember that the density of CO2 is 1.52

     There is a link to this at the top of the page....I really like it....So here it is again  Convert.exe DOWNLOAD IT! if you haven't already.

                                     High Pressure & Liquid CO2 Valves ...........HYCONTROL 

                              High Pressure Burkert Solenoid valve
                                                 This is the valve used on MANY Full Pressure European Flippers.

         This valve only has a pressure rating of 50 bar BUT it has been re-tested and approved for the higher 66 bar ( 1000 psi ) used in Fighting Robots.
               Note that over-volting of the std 24v solenoid is necessary for a satisfactory activation at 66 bar OR use a 12v solenoid coil @ 24v.

            The Burkert 5404  The above chart shows American specs for the same valve .... Note:- The Non- UL version has the 50 bar rating

                              PDF Files                        European             American

                                                                      QEV's   Quick Exhaust Valves

                              These have good flow rates compared to a standard 2/2 or 5/2 spool valve ......perhaps 3 times better.
                                                           Consider it's use as an inlet valve instead of an exhaust .

                      Need a regulator ..Get the Victor SR310    Take the link TWICE!
Victor SR-311-320 Carbon Dioxide Regulator
                                                                                       Part No :-

                                                                                 PDF File for the Victor....