Understanding Dewars & Cylinders

06, Jan. 2025

 

Understanding Dewars & Cylinders

Medical grade CO2 has 99.99% purity rating. Both Beverage and Food grade CO2 both have a 99.95% purity rating. Industrial CO2 has a 99.90% purity rating. The other .09 ' 1% is made up of impurities such as hydrocarbons or nitrogen. The slight difference between Industrial-grade CO2 and Food grade CO2 is the type of test that are done to qualify CO2 as Beverage gas compared to Industrial-grade. Food grade CO2 is in fact Beverage grade CO2, they are equivalent. Its all about the purity of the gas. All CO2 is made the same (to the best of our knowledge). Its all about how the CO2 is stored, handled and transferred. The FDA has put compliance laws on Food aka Beverage grade CO2, making distributers store the gas in specific tanks just for Food or Beverage grade. Food grade CO2 is pure enough for human consumption based on FDA compliance. Food-Grade, anything (in the US) means special requirements on transport and handling, which implies more expense. So even though the same plant may produce it, the pipes leaving the plant have to be Food grade, the tanks the product goes into have to be Food grade. The non-food grade version will go through less expensive /less-maintained/less-cleaned pipes and into similarly treated containers. Medical grade CO2 is not reasonable to get for consumption purposes.

Runfeng are exported all over the world and different industries with quality first. Our belief is to provide our customers with more and better high value-added products. Let's create a better future together.

When talking about cylinders we must first consider high pressure vs. low pressure. HPA (High Pressure Air) tanks are pressurized up to the tank's rating of psi or psi (Pounds per Square Inch). The pressure is then regulated through the tank's regulator down to 850psi (High Output) or 450psi (Low Output). High pressure vessels are generally referred to as tanks, whereas Low pressure containers are generally referred to as dewars. Many people use the word 'dewar' to describe a 'liquid cylinder', and vice versa. There are some key differences and they come in a wide variety of options.

While dewars might seem complicated at first, in reality they're safe and easy to use once you understand the basics. If you're interested in talking with an expert about how liquid CO2 trimming and sifting can radically improve efficiencies at your operation, contact us today to talk to one of our post-harvest processing experts.

We will now focus on Liquid Cylinder operations
for use with 
The Original Resinator.

When utilizing The Original Resinator in a commercial application, CO2 Cylinders similar to the Liquid Cylinders pictured above are very popular. This is do to the nature of large volume production needs, cost savings and convenience. Typically there are three valve handles, a pressure gauge, and a CO2 level indicator located on the top of the Liquid CO2 Tank. These valves handles should be labeled as Gas/Vent, Liquid, and Pressure Builder. We only use the Liquid supply to operate The Original Resinator. We will cover each of these below.

Before we dive into the tank valves we will briefly review the two types of outlets found on Liquid Cylinders, the CGA-622 and the CGA-320 outlets. Tanks outfitted with a CGA-622 or a female end, will need a CO2 liquid cylinder adapter, an essential component for hooking up your Resinator to a low-pressure liquid cylinder. If your cylinder has a CGA-322 outlet then your Resinator coil assembly included with your machine purchase is all you will need.

The top of a liquid cylinder tank ' a standard CO2 source for Resinator machines ' can be a confusing sight at first. Each outlet and valve serve a particular purpose, so each are important to understand. Since each outlet and valve should be clearly labeled, let's zero in on the most critical one for a Resinator machine: the Liquid outlet. This is the source of our liquid supply of CO2. This outlet is the one you'll use for all Resinator machines, but it's important to know that you may need a particular CO2 tank adapter to hook up to the outlet properly. (Adapter not provided with Resinator purchase.) Until recently, Dewar/Liquid Cylinder tanks came standard with liquid CO2 outlets called a CGA-320, allowing you to then attach a hose between the outlet and Resinator machine. That's changed. Liquid cylinder tanks are now coming standard with a female CGA-622 outlet, and therefore require a new CO2 tank withdrawal adapter, the CGA-622 x 320, to fit properly to a hose. If your liquid cylinder has a CGA-622 this Liquid Dewar adapter is now a necessary part of a secure setup so that your machine functions properly. It's a minor change, but it's important to make sure that you're using the correct fitting when dealing with liquids and gases at such pressures.

Are you interested in learning more about What Is a Dewar Tank?? Contact us today to secure an expert consultation!

*CGA-622 X 320 Liquid Cylinder withdrawal adaptor.
(Pictured below and available through our online store.)

Once you have identified the Liquid valve and are using withdrawal adapter (if necessary), it's time to attach the hose. The CO2 supply hose is threaded onto the valve outlet, being sure to use the appropriate sealing washer, and tightening to mitigate any leaks. Being that the Resinator is not a closed loop system, a few CO2 leaks are nominal. Although leaks will contribute to raised CO2 levels, which should always be monitored. When ready to operate the Resinator, open the Liquid valve fully by turning counter clockwise. The pressure builder is a very important component in achieving the proper Resinator operating pressure. We can monitor this operating pressure by observing the pressure gauge located on the top of the Liquid CO2 Tank. Ideally the operating pressure of the Liquid CO2 Tank is 330-350 psi. This is achieved by opening the pressure builder valve prior to operating the Resinator.

Notes:
  • The relief valve may hiss for pop if the pressure build beyond the relief valve rating and this is normal.
  • The Liquid CO2 Tank is equipped with a pressure relief valve that is fixed to open at 350 psi. (Be sure to get a 350 psi tank.) The pressure relief valve is in place to ensure the internal Liquid CO2 Tank pressure does not exceed 350 psi. As you approach the ideal operating pressure the relief valve may open slightly and release CO2 gas. Although this is sometimes noisy this is no cause for alarm, simply close the pressure builder valve by turning clockwise.
  • A tank with a dent or dig may not work as good.
  • You must make sure the pressure build is on 300- 350 range.
  • TECH TIP: Building the pressure to the proper level may take up to an hour, so it is suggested that the Pressure Builder valve be fully opened one to three hours before use.
  • Never use the gas side, purge tank before liquid use.
  • Tanks are extremely heavy and a tank dolly is recommended when moving.

Know Your Gauges and Valves

Tell help you see the forest from the trees, take a look a the diagram below to become familiar with the important parts of your liquid cylinders. Be sure to get request

Economizer Circuit

If you don't use the a cylinder for several days, pressure will continue to rise at a rate of apox. 30 psi per day because a small amount of heat will leak into the inner tank. This heat vaporizes a small amount of liquid and causes the pressure to slowly rise. The pressure may build up to the design of your Pressure Control Valve. The valve will then open and vent gas to the atmosphere. To minimize losses from this venting, the cylinders have an Economizer Circuit. The Economizer Circuit comes into action when the pressure reaches psi setting. At this point, the regulator allows gas from the top of the tank to flow through the internal vaporizer out of the Gas-use Valve to the target system. This reduces pressure in the inner tank and minimizes losses from venting. When pressure normalizes, the Economizer Regulator closes and the cylinder then deliveries gas by drawing liquid through the Vaporizer Circuit. The Economizer Regulator should have a set pressure 15 psi higher than the Pressure Building Regulator.

Pressure Gauge

The Pressure Gauge is probably the one you will look at first and refer to most frequently. This gauge indicates gas pressure inside the inner tank. Since cryogenic liquids are actually liquefied gases, pressure within the tank will constantly increase as the laws of physics transform the cold liquid into warmer gas. Fortunately, this pressure will help you withdraw the liquid or gas from your cylinder. But for most applications, the pressure inside the tank must be artificially maintained. A Pressure Building Circuit can automatically do that.

Opening the Pressure Building Valve located at the top of the tank takes liquid from a line that runs from the bottom of the inner tank, and passes it through the Pressure Building Coil attached to the inside wall of the outer tank. As liquid passes through the Coil, it is vaporized by the heat of the outer tank. The resulting gas is fed through the Pressure Building Valve and Pressure Building Regulator, into the inner tank causing the pressure to rise. We recommend operating your cylinder at 350psi to avoid any clogging/freezing issues while under operation with your Resinator.

If you want to learn more, please visit our website microbulk.

Acquiring a LOX dewar?

You may not be able to place a filled LOX dewar in the bed of your truck and drive off with it. LOX transport is subject to regulation. Not an issue if the LOX supplier can come to you, of course.

Have you investigated medical equipment suppliers?
example:
http://www.cryopal.com/en/cryogenic-needs/providing-oxygen-to-patients-at-home.html

A good point raised!  I just found our local regulations:

Icelandic Regulations

Section 14, "Flutningur", covers transportation.  A translation would be:

"General: Oxygen shall not be transported in vehicles except in an area separated from the drivers' section.  One must ensure sufficient ventillation and stability of the container.  Ensure that it is closed during the shipment.  Liquid oxygen shall be shipped in isolated tanks with pressure 1 to 25 bar.  In pressurized tanks there must be a safety lid/vent.  One must follow all of the applicable ADR rules"

Not knowing what the ADR rules are, I found them here:

ADR rules

"ADR-Handbook: Shipment of dangerous cargo"

It seems to be about the "European Agreement concerning the International Carriage of Dangerous Goods by Road".  So, for an English version:

http://www.unece.org/trans/danger/publi/adr/adr/15contentse.html

In there I see that LOX is UN no. , clas 2, code 3O, Labels 2.2 +5.1, Limited and excepted quantities 0 under sec. 3.4 / E0 under sec. 3.5.1.2, Packing instructions P203, Mixed packing instructions MP9, Instructions T75, codes TP5, TP22

Looking up E0, it basically means no exceptions.

P203 begins on page 84.  It requires section 4.1.6; chapter 6.2; insulation to prevent the formation of frost; the container being able to tolerate at least 1.3 times its maximum pressure; the container not filled to more than 98% what it would be filled to if it were filled with water at 1 bar; a pressure releif device; compatible materials; and inspected once at least every five years in accordance with 6.2.1.6.3, once every 10 years for non-UN closed cryogenic recepticals in accordance with 6.2.3.5.2.

MP9: May be packed together in an outer packaging for combination packaging with class 2 goods, with goods of other classes which allow mixed packing, and with non-ADR goods, provided they do not react dangerously.

T75, TP5: Must follow the filling requirements in section 4.2.3.6

T75, TP22: Lubricant for joints or other devices shall be oxygen compatible

...

I don't see any problems there    Looks like you basically can just have it in the bed of a pickup truck, so long as it's strapped down, properly marked, a regulation tank, properly filled, etc.

Re, cryopal, I doubt they're going to come to Iceland    As mentioned, there's only one supplier in the country: Ísaga.  You should know that we don't exactly have "selection" here, there's only 330k people in the whole country    Plus, even if there was a delivery service that didn't charge an arm and a leg, I'd still need a dewar either way.

Edit/Lar: fixed long URLs. Please use the URL tag properly in future, thanks.
Don't buy one. Any major supplier should be able to rent one with the LOX. Checkout Praxair or Airgas. Don't blow yourself up. Cleanliness is vital.

As mentioned earlier, the only LOX supplier in the country doesn't even have one, they only have LN2 dewars (they were at first going to sell me LOX in them... we talked about it and both decided that wouldn't be smart... particularly when I learned that they don't even have lids!).  Do recall that I'm not in the US.  The only supplier in Iceland is Ísaga, our local division of the Linde group.

I've read through lots of LOX handling guidelines; I know to treat the stuff with respect.  I'm just going to stick with the general rule of "if you're ever having it touch anything organic, whether a large object or just a thin film on a surface, just go ahead and assume that it's going to start aggressively combusting".  I know that technically LOX isn't hypergolic with that many things, but does become shock sensitive with most organics, and I'll just treat "shock sensitive" as "hypergolic" to stay on the safe side     And of course no titanium either, since it's also shock sensitive with LOX.

Ah, this is what I get for skimming and making assumptions. I apologize for the confusion.