Frequently Asked Questions — Cryogenic Tank Level

Before Use

Q. How does a differential pressure (dp) gauge measure level in a cryogenic tank?

A. A differential pressure (dp) gauge has two ports, a high pressure port and a low pressure port. On a cryogenic tank the high pressure port of the gauge is piped to the bottom of the tank. Since the tank is pressurized the low pressure port of the gauge is piped to the top of the tank, the vapor space. The difference between the high and the low pressures then represent the height of the liquid only. On Orange level gauges, differential pressure is relayed to the gauge through a magnetically coupled sensor-indicator design.


Q. How do you calculate the range required for a dp level gauge on a cryogenic tank?

A. Cryogenic tanks have an inner and an outer tank. Multiply the height of the inner tank by the specific gravity of the liquid. Then multiply by .90 to account for the top 10% of the tank occupied by the ullage or vapor space. This 10% is typical, not a standard factor. The calculation becomes, Height (inches) x SG x .90 = XX inches H2O. For more detail on this or for assistance in calculating the level range for your tank contact Orange.


Q. What size tanks can Orange Research gauges and transmitters be used on?

A. Orange has level gauges or transmitters for all size tanks, including liquid cylindersmicro-bulk tanksbulk tanksISO tanks and trailers. For more details on matching your tank to an Orange solution please contact us.


Q. What gases can Orange level gauges be applied to?

A. LIN, LOX, LAR, CO2, LNG. For information about matching your gas to an Orange level gauge please contact us.


Q. How do I specify an Orange level instrument?

A. Each product page has a How To Order section which steps you through the features required to complete a configuration of your gauge. You can contact Orange directly for assistance.


Q. What units are available for your scales?

A. Most common scales are in InchesH2O, but psid, bar, kPa, gallons, liters, % and many others are standard.


Q. Do you have level transmitters for Telemetry?

A. Yes, Orange has dp level transmitters that are commonly integrated into Telemetry systems. They are a standard option for adding to a gauge, or as a transmitter only, with no gauge. The outputs are 4-20mA (2-wire) or 0-5Volts. The outputs of our wired transmitters are fed to the telemetry systems. To discuss integrating our level transmitters into your telemetry system contact us directly.


Q. Can Orange level gauges handle the cold temperatures of cryogenic liquids?

A. The liquid in a cryogenic tank is boiled off to a gas by the time it reaches our gauges, so the temperatures are quite warm relative to the liquid phase during storage. So, there is no problem with the cold temperatures actually coming into contact with our level instruments.

Before Use

Q. Can Orange level gauges or transmitters be used in cold outdoor environments?

A. Yes, Orange level products are able to handle the coldest temperatures in the coldest environments. They have been used successfully above the Arctic circle, for decades, with no reported problems.


Q. Can Orange level gauges withstand the shock and vibration common on transported tanks or trailers?

A. Yes, in fact the Orange level gauge design is uniquely qualified for such use. We incorporate a magnetically coupled sensor-indicator design, which allows for frictionless movement, so there are no mechanical linkages to wear or break. This means no recalibration or repairs are necessary, resulting in care-free operation for many years.


Q. What types of valves are recommended for a dp level gauge?

A. One isolation valve for the high pressure port, and one isolation valve for the low pressure port, and an equalizer valve are recommended. A three way manifold valve incorporating all three is common. Orange has a level gauge solution with an integral 3 way valve.

Note: The valves should always be opened and closed slowly. Although Orange level gauges are rugged and reliable, they are still sensitive instruments.


Q. Does Orange Research have level gauges that replace Barton or Prime level gauges?

A. Yes, Orange level gauges have been replacing Barton and Prime gauges for many, many years. On some models we can actually match the mounting hole and porting patterns on the Barton gauges exactly. Contact Orange for more details.


During Use

Q. Why does the level reading on the tank read below full when my tank is newly filled?

A. During filling, a cryogenic tank often experiences higher than normal operating pressures. This higher pressure can lower the specific gravity of the liquid, which lowers the pressure on the high pressure port of our instrument, which in turn lowers the level reading. For more details on this please contact Orange.


Q. Why does my level reading fluctuate over time with no usage?

A. When the ambient temperature changes upwards this change is also slowly transferred into the cryogenic tank. This higher temperature raises the tank pressure, which in turn decreases the SG of the liquid and lowers the level reading. downward the reverse occurs. To better understand the effects of pressure and temperature variations on your tank level reading please contact Orange.

WARNING: Some of our products contain Nickel, a chemical known to the State of California to cause cancer. For more information go to:

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