The old saying goes something like:
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To know someone is to love them.
If people count on you to supply liquid nitrogen or other cryogenic liquids for storing biological samples or processes like Liquid Chromatography Mass Spectrometry (LCMS) and Molecular Beam Epitaxy (MBE), the saying can apply to your relationship with your dewars and liquid cylinders.
Because, most of the time, things are good.
But when things go bad (you unexpectedly run out of liquid, liquid stops flowing, or your floors get water damaged), the more familiar you are with the operations and maintenance of your dewars and liquid cylinders, the faster you can make things better.
This post will reacquaint you with a key piece of equipment ' dewars and liquid cylinders ' so that you can quickly solve problems and resolve issues that keep you away from your numerous #1 priorities.
Many people use the word 'dewar' to describe a 'liquid cylinder', and vice versa. There are some key differences.
Liquid cylinders are pressurized containers specifically designed for cryogenic liquids. Liquid cylinders let you withdraw liquid and/or gas.
A liquid cylinder has valves for filling and dispensing the cryogenic liquid, and a pressure-control valve with a brittle rupture disk as backup protection.
Dewars are non-pressurized vessels, like a Thermos Bottle. They typically have a loose-fitting cap or plug that prevents air and moisture from entering while allowing excess pressure to vent.
Laboratory dewars have wide-mouthed openings and do not have lids or covers. Laboratories primarily use these small containers for temporary storage.
The remainder of this post focuses on Liquid Cylinder operations.
To become familiar with the important parts of your liquid cylinders, take a look a the diagram below:
The Pressure Gauge is probably the one you will look at first and refer to most frequently. It indicates gas pressure inside the inner tank.
Since cryogenic liquids are actually liquefied gases, the pressure within the tank will constantly increase as the laws of physics transform the cold liquid into warmer gas. 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 the 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.
When the pressure has been built, you can draw gas from your cylinder by opening the Gas-use Valve. Opening this valve lets the pressure in the tank force liquid up a withdrawal line, and then down into a vaporizer coil. Once again, heat is conducted through the outer tank walls to the vaporizer.
As the liquid moves through the coil, it is vaporized by this heat. The resulting warm gas flows up through the Gas-use Valve out to the user system to complete the Vaporizer Circuit.
Generally, a single-stage regulator is attached directly to the Gas-use Valve to reduce the supply pressure to match your application's requirements.
If you don't use the cylinder for several days, pressure will continue to rise at a rate of 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 140 psi.
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 your 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 delivers gas by drawing liquid through the Vaporizer Circuit. The Economizer Regulator should have a set pressure of 15 psi higher than the Pressure Building Regulator.
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The Pressure Control Valve is mounted on the same stem as the Pressure Gauge. Often set to open at 230 psi, the Pressure Control Valve works in conjunction with a Rupture Disc in the inner tank.
As a secondary relief device, there is also a Burst Disc on the outer tank to protect the space between the inner and outer tanks from high pressure.
To withdraw liquid from your cylinder, first close the Pressure Building and Gas-use Valves. Then open the Liquid-use Valve to allow head pressure in the tank head to force liquid up to the withdrawal tube and out the Liquid-use Valve.
Liquid withdrawal should be done at low pressure to prevent flash losses. During the transfer, if the pressure in the tank is higher than the normal liquid withdrawal pressure, open the Vent Valve to lower the pressure. Before withdrawing liquid, liquid is typically withdrawn at less than 15 psi.
When filling an open container, if a greater liquid withdrawal pressure or rate is required, a qualified service agent can adjust the Pressure Building Regulator.
A Liquid Contents Gauge is in the center of the tank. This can be a float-type gauge that provides an approximate indication of the tank's contents.
If you want more accurate measurements, try a gauge that uses differential pressure to determine liquid levels. These modern devices also contain graphical digital displays to give you precise measurements. They also often have the intelligence to eliminate the need for lookup charts.
In addition, many of these digital liquid content gauges have telemetry capabilities to make it easier to monitor the levels of key cylinders.
Because the Pressure Building Vaporizer contains cold liquid, it cools the outer tank. It's perfectly normal for frost to form on the outside of the cylinder. During a prolonged high draw, the gas-withdrawal temperature falls considerably, and the outside of the cylinder will be very heavily frosted.
This frost eventually turns to water that can damage flooring or seep into your facility's interstitial space to create more damage to other systems.
A Drip Tray can save you a lot of headaches and hassles. Place your liquid cylinder and/or its vaporizer on a pan or tray to catch the water as the frost evaporates. The higher the tray's lip, the less worry you'll have about water damage.
The more you know about your dewars and liquid cylinders, the less you have to worry about them.
If you think something has gone wrong, just remember:
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.
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.
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.
*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.
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
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.
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.
Contact us to discuss your requirements of Liquid Oxygen Dewar. Our experienced sales team can help you identify the options that best suit your needs.