Questions You Should Know about Liquid Dewar Cylinder

17 Mar.,2025

 

Understanding Dewars & Cylinders - The Original Resinator

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.

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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/VentLiquid, 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.

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*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.

Are you interested in learning more about Liquid Dewar Cylinder? Contact us today to secure an expert consultation!

Basic Intro to Liquid Cylinders - Earlbeck Gases & Technologies

Throughout history, humans have used containers to store, transport, and dispense items. Regardless of the era, it is generally the case that what's inside a container is more important than the container itself. However, when it comes to cryogens, the considerations and specifications behind their storage cylinders give these containers special notoriety.

In order to properly choose and use liquid cylinders, it is important to understand their make up as well as any considerations for their care and storage.


What are Liquid Cylinders and What are They Used For?

A liquid cylinder, sometimes called a 'liquid flask' and most commonly known as a 'dewar' is a double-walled, vacuum-installed container used for storing cryogens. A dewar acts like a thermos in that it keeps atmospheric gases well below ambient temperatures (sometimes as low as -400 degrees F) so that they are stored in their liquid states. 

Commonly stored cryogens include liquid nitrogen, liquid argon, liquid oxygen, and liquid helium. Depending on the design and features, dewars can dispense the elements as gas, liquid, or both. Although dewars used for temporary storage may be made out of foam insulation, most are made from metals such as aluminum or steel.

Cryogens themselves are used in many applications, such storing food, cooling superconductors, and freezing lab samples. They are also used in MRI machine functioning, producing cryogenic fields for rockets, and performing cryosurgeries. 

The benefit of dewars is that just one of them can function like many gas cylinders. This superpower is achieved by the dewar's ability to house pressure far larger than its natural productive capacity. Because their functionalities can be equivalent to 20 high pressure cylinders, it is easy to surmise that even a single dewar can save precious storage space while significantly cutting back on costs.
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Anatomy of a Liquid Cylinder

The construction of a liquid cylinder can be simple or complex depending on its purpose. 
Although common working pressures include 22, 180, and 230psi, dewars can be custom designed to accommodate other pressures. Although a cylinder is the most-common shape, dewars can also be crafted into other dimensions. Additionally, they can be outfitted with handles, legs, various drain locations, outlets, and caster mountings ' whatever is needed to help the dewar fulfill its intended use.

Regardless of the shape they ultimately take, most dewars share the same, internal anatomy. The most visible part of a dewar is the outer vessel, which is the metal surface that makes up the dewar's shape and protects the inner vessel where the liquid tube and vent tube are often housed.

The combination of the outer and inner vessels allows the dewar to function. Opening a pressure building valve at the top of the tank draws liquid through the liquid tube and through a pressure building coil. As the liquid travels through the tube, it transforms into its gaseous state by the warmer temperature outside of the inner vessel. This process, sometimes known as the Vaporizer Circuit, increases pressure within the canister that can be harnessed to dispense the gas.

Many cylinders have an Economizer Circuit which prevents gas losses from venting by storing extra pressure that may build up when the cylinder remains unused for a time.  When the internal tank pressure reaches a specific psi, a regulator allows gas to flow through an internal vaporizer in order to reduce inner-tank pressure. When pressure normalizes, the regulator closes and the cylinder functions normally.

At the top of most dewars is a system of gauges and valves responsible for monitoring and releasing the gas. As its name suggests, the pressure gauge indicates the pressure inside the inner vessel. Typically attached to the pressure gauge is a pressure control valve.
The gas-use valve and liquid-use valve draw gas or liquid forms out of the dewar for use.  The pressure building regulator controls the rate of pressure build while a liquid contents gauge measures how much liquid is left in the tank.


Care and Considerations

It is beyond question that caring for cryogens and their storage containers requires careful consideration. 

First, it is important to have a working knowledge of the different types of gases and what each might do under certain conditions. For example, since frost often form outside of dewars due to prolonged usage or a pressure valve being left open, it is advisable to keep a drip tray or pan under the dewar to avoid water damage. 

Second, it is important to know and follow each cylinder's specifications and instructions exactly. Cryogens should NEVER be stored in containers that are not specifically designed for them because each cylinder has different venting and temperature regulation abilities.  This logic also applies to any hoses, valves, regulators, gas detectors, or other containers that may be involved in manipulating the cryogens. While there may be room for error in storing/transporting some substances, cryogens are not among them.

Third, it is important to know how to protect the person who will interact with the cryogens and liquid cylinders. Safety equipment, including glasses, gloves, face shields, closed toed shoes, lab coats or other protective clothing, etc. should be used at all times. Whenever possible, the person working with the dewars should receive any training or instruction that is available on use and safety/emergency practices. Please consult with your gas supplier for the latest training on safe handling procedures.
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Final Thoughts

When proper care is given to operating liquid cylinders, their economic, industrial, and scientific benefits can be enjoyed.  While it may require extra effort, keeping educated about the anatomy of the cylinders, the nature of the atmospheric gases that they house, and current safety practices will ensure that dewars and their contents achieve their purposes.