Siphon vs Non-Siphon Gas Tanks
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What is a Siphon or Dip Tube?
A siphon, sometimes referred to as a dip tube, is like a straw, one normally made of either steel, stainless steel, or copper. There are two different types, with one being external, and another that goes inside and reaches the bottom of the tank. A straw inside of a gas cylinder is typically referred to as either a siphon or dip tube, though some may call it a liquid straw, depending on the region and industry. A tank with a siphon inside is typically referred to as a siphon tank, but are sometimes known as liquid cylinders too.
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Similarities Between Regular and Siphon Cylinders
CO2 cylinders and siphon tanks come in different materials, like aluminum and steel, and can be ordered in a variety of sizes. Its measurements are based on weight, typically from between 5lbs and 50lbs. The siphon is out of sight, staying inside the tank. Because of this, they both look the same on the outside. To compensate for the visual similarities, a cylinder will be marked a certain color to identify whether it has a dip tube inside or not. The color itself may vary depending on the company and region. While the latter is the only specific visual difference compared to regular gas tanks, there are a few technical features that make them stand out from the rest.
Differences Between Regular and Siphon Cylinders
Most gases are stored in their liquid state. That liquid gas gets sucked up to the valve, bringing its state of matter into its gaseous state out of the tank. Introduce a dip tube, and it will instead allow the flow of the gas to expel in its liquid state. Some people refer to them as liquid tanks or liquid cylinders for that reason. Besides the physical color marking and internal dip tube itself, a siphon tank will look exactly like a regular gas tank, but their applications vary greatly because of what the dip tube is designed to do.
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Now first off, siphon tanks are less commonplace compared to regular, siphonless tanks. Carbon dioxide tanks dedicated to carbonating water and soda, helium tanks blowing balloons, and propane tanks heating grills will not have internal siphons. Although, that doesn&#;t mean gas tanks with dip tubes don&#;t have a place or purpose.
Applications For Siphon Tanks
There are specific jobs that will put liquid gases to good use, and that&#;s where the siphon comes into play! It plays a role in food preservation by refrigerating and storing food for extended periods of time. In some cases, it can aid in softening food too.
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It also helps in extracting solvents. Many extraction systems use liquid CO2 because the gas has the ability to separate and dissolve certain substances, making the yield of separated solvents possible. Using liquid CO2 is the cleanest and quickest way to perform this task. Other methods that don&#;t use it require more time, along with an additional purging process. This efficiency wouldn&#;t be possible without that siphon inside the CO2 tank. Although, a specific CO2 grade is used for extraction systems, specifically one called supercritical fluid extraction grade (or SFE-grade for short). While we don&#;t carry that type of grade, it at least goes to show what liquid CO2 is useful for.
Can Any Gas Use a Siphon?
For the most part, yes, but the specifics vary for each gas cylinder. Carbon dioxide tanks are typically given the option of having an internal dip tube. Most other gases probably won&#;t use that type, but will instead use an external siphon.
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Also, not every gas is stored in their cylinder the same way. For example, to be used in its liquid state, oxygen must be stored in a dewar tank. On the other hand, liquid CO2 can be stored in a cylinder. Different gas container types and sizes will keep their gases at specific pressures and temperatures. Otherwise, they may not remain in their proper state of matter inside or outside the tank.
Siphon CO2 Cylinder Safety Concerns
First off, it&#;s imperative that you don&#;t accidentally get liquid CO2 out of your siphonless cylinder, or gaseous CO2 out of your siphon CO2 tank. In most cases, the gas&#; wrong state of matter is due to the mistake of ordering the wrong type of cylinder. If this isn&#;t the case however, then the error may be due to improper handling of the gas cylinder itself, where it&#;s being used upside-down instead of right-side up.
Gas cylinders should remain right-side up at all times. If your CO2 tank, with or without a siphon, is sitting upside down, you risk breaking the gas regulator, leaving an opening on the top of the tank and turning it into an unpredictable rocket. At that point, property damage and severe injuries can quickly occur. The room can also displace oxygen with an overabundance of carbon dioxide, making anyone in the room feel physically ill and have difficulty breathing until it ventilates out and everyone gets fresh air.
Even if the valve doesn&#;t break or the tank doesn&#;t fall in this position, it will improperly spray liquid CO2 instead of gaseous CO2. If you absolutely need liquid CO2, an upside down tank is not the way to do it. That&#;s what a siphon cylinder is for. If you do this with a siphon CO2 tank, you will get gaseous CO2 instead of its liquid form. Still, putting it upside down isn&#;t appropriate or safe, so you simply need to just swap out your siphon CO2 tank with a siphonless one.
When it comes to storage, siphon CO2 tanks follow the same rule as other gas cylinders. Keep them in a cool and dry location, sitting upright, secured with storage equipment, and away from obstructions, hazards, and all forms of heat. Doing these things prevent them from unnecessary damage, the exposure of flammable materials, harmful temperatures, and the risk of falling and rolling around.
It&#;s important to understand the many safety concerns regarding gas cylinder operation and storage. There are many different types of safety equipment to use and proper safety protocols to follow too. You can see our collection of articles that focus on safety to learn more.
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Contact us to discuss your requirements of Lng Cryogenic Storage Tank. Our experienced sales team can help you identify the options that best suit your needs.
Ordering Siphon CO2 Cylinders
Our CO2 cylinders are available in different sizes, with or without an internal siphon. We also have a collection of safety equipment to look at in our online shop. As for the tanks themselves, you may rent as many as you need from our ordering page.
If there are any questions or concerns, please feel free to contact us. Call one of our associates at 877-280-, and one of our customer service representatives will be more than happy to assist.
Or &#; How to Dodge Dewar Bullets
The old saying really goes something like:
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 you numerous #1 priorities.
Tomāto, Tomăto &#; Dewar or Liquid Cylinder
Many people use the word &#;dewar&#; to describe a &#;liquid cylinder&#;, and vice versa. There are some key differences.
What is a Liquid Cylinder?
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.
What is a Dewar?
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, yet allows 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.
Know Your Gauges, Circuits and Valves
To 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.
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.
Gas-use Valve and the Vaporizer Circuit
When 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.
Economizer Circuit
If you don't use the a 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 come into action when the pressure reaches 100 40 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 the 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 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 Control Valve and Rupture and Burst Discs
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.
Liquid-use Valve
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 withdrawal tube, and out the Liquid-use Valve.
Liquid withdrawal should be done at low pressure to prevent flash losses. During transfer, if 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.
Don&#;t get Caught Dry: Liquid Contents Gauge
In the center of the tank there is a Liquid Contents Gauge. This can be a float-type gauge that provides an approximate indication of the tanks contents.
If you want more accurate measurements, try a gauge that uses differential pressure of determine liquid levels. These modern displays also contain graphical digital displays to give you precise measurements. Plus they 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 levels of key cylinders.
Watch out for Frost and Water
Because the Pressure Building Vaporizer contains cold liquid, it cools the outer tank and it is perfectly normal for frost to form on the outside of the cylinder. During a prolonged high-draw, the gas-withdrawal temperature to fall considerably and the outside of the cylinder will be very heavily frosted.
This frost eventually turns to water that can damage flooring, as well as 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.
So What?
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:
- The Pressure Gauge indicates pressure inside the inner tank. Opening the Pressure Building Valve increases tank pressure to normal operating levels.
- The Gas-use Valve allows gas to flow from the tank.
- The Economizer Circuit minimizes product loss.
- To draw liquid, close the Gas-use and Pressure Building Valves, and open the Liquid-use Valve.
- If you need to know exactly how much liquid is in your cylinder, use a Digital Gauge.
- Frost and ice are nothing to be scared about. But use a drip tray or pan to avoid water damage.
But if you do need help, make sure that your liquid nitrogen, argon or helium is set-up to get you a solution when you need it. Whether it be an emergency delivery, or just being talked through a problem, a good cryogenic supplier like But if you do need help, make sure that your liquid nitrogen, argon or helium is set-up to get you a solution when you need it. Whether it be an emergency delivery, or just being talked through a problem, a good cryogenic supplier like WestAir is good to have around. Contact us today for a quote and consultation.
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