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Gas Mixers


INDOOR MODELS 6105, 6205, 6305, 6405

Indoor Model
  • 0-2000, 0-5000, 0-10,000, and 0-20,000 SCFH Flowrate Models
  • Continuous gas analysis of the gas mixture, optional alarms available
  • Surge tank design produces a constant gas mixture proportion from shutoff to full flow conditions

OUTDOOR MODELS 8105, 8205, 8305, 8405

Indoor Model
  • Same benefits of indoor design plus a NEMA 4 enclosure for protection from weather or tampering
  • The analysis has a heated cell chamber for functioning at outdoor temperatures


The Thermco gas mixer is designed to mix two non-flammable and non-corrosive gases. The gas mixer is normally used with a process where the supply gases are drawn from bulk sources and the mixture is produced on-site where it is supplied to the process by a pipeline. The system is designed for applications that require a very reliable production for mixed gas on a continuous basis. Some of the common applications for the gas mixer are:

Common applications include shield gas for welding, leak detection mixtures, cover gas for molten metals and lamp filling mixtures.

Because the gas mixer uses a surge tank design, this type of system is ideal for applications that require maintaining a precise proportion from full mixed gas flow down to zero flow.

Examples of Possible Mixtures

Gas Mixtures Applications
Carbon Dioxide/Argon Welding Shield Gas
Oxygen/Argon Welding Shield Gas
Helium/Argon Welding Shield Gas
Carbon Dioxide/Nitrogen Food Packaging
Oxygen/Carbon Dioxide Food Packaging
Helium/Nitrogen Leak Detection
Helium/Air Leak Detection
Helium/Air Blanketing Atmosphere
Nitrogen/Argon Lamp Filling

Special Designs

Special Mixing System with 1060 Gallon Surge Tank
Special Mixing System with 1060 Gallon Surge Tank

Customized designs are frequently manufactured for specific customer requirements.

Food Packaging- Stainless steel NEMA 4X enclosures and stainless steel surge tanks are available for harsh washdown environments in food processing areas. Higher than standard mixed gas outlet pressures are available.

Leak Detection- These systems often require high mixed gas outlet pressures (up to 400 PSIG). These applications should be discussed with the Thermco sales engineer to determine the best design based on available inlet pressure and required accuracy.

Blanketing Atmosphere- These applications require the creation of an oxygen/nitrogen mixture. The mixture may be created from air/nitrogen or oxygen/nitrogen supplies. Because the thermal conductivity of oxygen and nitrogen are very similar, the Thermco thermal conductivity gas analyzer can not be used in these applications. Instead, an oxygen specific analyzer is utilized, based on the electrochemical fuel cell or paramagnetic principle. Gas mixers for this application are frequently built for non-standard pressure conditions and flowrates higher than 5000 SCFH.

Lamp Filling- Precise mixture of nitrogen and argon are used for lamp filling. Special construction to minimize particulate and impurities in the gas mixture is available for this application.

Thermco Gas Analyzer

Gas Analyzer
Gas analyzer calibrated for carbon dioxide
in argon, indoor model.

The gas analyzer constantly monitors the mixture produced by the system. The analysis will immediately detect an improper gas mixture being created by conditions such as low pressure in one of the supply gases, a malfunction in the mixing system, or gross contamination in one of the supply gas streams.

The analyzer in the mixing system is a thermal conductivity type manufactured by Thermco. This analyzer is ideal for measurement of two gas mixtures. Calibration of the gas mixture with a known gas is recommended once a year. The weatherproof type gas mixers utilize a thermal conductivity gas analyzer with a temperature controlled detector chamber. For more details on the thermal conductivity analyzer refer to Thermco gas analyzers models 7000 & 7010.

Alarm System

All gas mixers come with an automatic alarm to alert personnel when an improper gas mixture is being created. All mixers come with a digital meter. The alarm includes high and low alarm contacts on the digital meter, a warning light on the analyzer, a horn that is mounted on the panel(or weatherproof enclosure), and a horn silence button.

In certain situations it may be required that the minor gas, major gas, or mixed gas be shutoff on an alarm condition. This can be accomplished if the factory is notified at the time the order is placed.

Gas Mixer Specifications

Flowrate Indoor Model Outdoor Model
0-2000 SCFH (0-53.6 Nm3/h) 6105 8105
0-5000 SCFH (0-134 Nm3/h) 6205 8205
0-10,000 SCFH (0-268 Nm3/h) 6305 8305
0-20,000 SCFH (0-536 Nm3/h) 6405 8405

Standard Ranges (Indoor and Outdoor Models):

  • 0-30% CO2 in Argon
  • 0-10% Oxygen in Argon
  • 0-50% Helium in Argon
  • 0-50% Helium in Nitrogen
  • 0-50% CO2 in Nitrogen

Gas Mixing Accuracy:

  • ±2% of full range over 60°F to 80°F (15°C to 27°C) temperature range
  • ±4% of full range over 32°F to 104°F (0°C to 40°C) temperature range
  • ±8% of full range of -10°F to 104°F (-23°C to 40°C) temperature range

Stated accuracy assumes that the input temperature of the gases are equal.

Gas mixer accuracies depend upon many variables, including frequency of analyzer zeroing and calibration, gas mixer maintenance, and environmental conditions around the gas mixer. These accuracies are presented as typical performance for these systems.

Flow Capacity:

Rated capacity of 0-2000, 0-5000, 0-10,000, and 0-20,000 SCFH is at midrange setting. Less capacity is available below midrange setting and more capacity is available above midrange setting. Consult Thermco for details on available capacity. Midrange setting is the middle of the gas mixer adjustment range, i.e., a gas mixer with a range of 0-30% CO2 in argon has a midrange setting of 15% CO2 in argon.

Temperature Range - Ambient and Process Gas:

  • Indoor Models: 32°F to 104°F (0°C to 40°C)
  • Outdoor Models: -10°F to 104°F (-23°C to 40°C)

Some large outdoor-style gas mixers (greater than 10,000 SCFH) will have higher minimum temperature ratings. Consult factory for details.

Normal Supply Gas Inlet Pressure Range:

  • 100-125 PSIG (6.9-8.6 barg) for major and minor gases for models 6105, 6205, 8105, 8205.
  • 120-145 PSIG (8.3-10.0 barg) for major and minor gases for models 6305, 6405, 8305, 8405.
Input pressures do not have to be equal.

Normal Mixed Gas Outlet Pressure Range:

  • 10-50 PSIG (0.7-3.4 barg) for models 6105, 6205, 8105, 8205.
  • 30-50 PSIG (2.1-3.4 barg) for models 6305, 6405, 8305, 8405.
Mixed gas pressures are adjustable with a regulator on the gas mixer.

Gas Connections and Piping:

For models 6105, 6205, 8105, 8205, 1 inch female NPT pipe for major, minor, and mixed gas connections. For other models consult the factory. Piping is brass and copper material.

Surge Tank:

30 gallon for Models 6105, 8105; 60 gallon for Models 6205, 8205; 120 gallon for Models 6305, 8305; 240 gallon for Models 6405, 8405; carbon steel, ASME coded, and CRN registered; pressure safety relief valve provided.

Solid-State Surge Tank Pressure Switch:

The gas mixer utilizes a solid-state pressure switch to control the surge tank pressure. A digital readout of the pressure is built into the switch. Both the sensing element and electrical switch are solid-state. An LED indicator shows when the surge tank is filling. Use of this pressure switch virtually eliminates the most common cause of gas mixer failure.

Power Requirements:

115 VAC, 50/60 Hz., 0.5 ampere. Acceptable voltage range 104-126 VAC. Available on request, 220 VAC. 50/60 Hz., 0.25 ampere. Acceptable voltage range 204-240 VAC.

Weight and Dimensions:

Model A B C Net Weight Crated Weight*
6105 55"(140cm) 41"(104cm) 26"(66cm) 230 lbs.(104 kg) 350 lbs.(159 kg)
6205 59"(150cm) 51"(130cm) 29"(74cm) 350 lbs.(159 kg) 500 lbs.(227 kg)
6305 71"(180cm) 74"(188cm) 34"(86cm) 680 lbs.(308 kg) 1000 lbs.(454 kg)
6405 76"(193cm) 89"(226cm) 40"(102cm) 1180 lbs.(535 kg) 1600 lbs.(726 kg)
8105 57"(145cm) 48"(122cm) 24"(61cm) 325 lbs.(148 kg) 425 lbs.(193 kg)
8205 61"(155cm) 54"(137cm) 25"(64cm) 440 lbs.(220 kg) 700 lbs.(318 kg)
8305 66"(168cm) 74"(188cm) 25"(64cm) 730 lbs.(331 kg) 1065 lbs.(483 kg)
8405 75"(191cm) 97"(246cm) 31"(79cm) 1230 lbs.(558 kg) 1690 lbs.(767 kg)
*These are crated weights for shipments to North America. Crated weights to other locations will vary.

Gas Analyzer Specifications

Principles of Operation

Thermal conductivity, manufactured by Thermco.


The range of the analyzer will be the same as the gas mixer, except for the 0-30% CO2 in argon gas mixer, which has an analyzer range of 0-50% CO2 in argon.

Analysis Indication

Analog meter versions, 4.5 inch (11.4 cm) meter, non-linear direct reading scale. The analog meter is only available on CO2/argon and oxygen/argon ranges. Digital meter versions, resolution 0.1%, direct readout in gas percent, built-in microprocessor-based linearizer.

Analysis Indication

4-20 mA, proportional to gas analysis range selected. This output is isolated and self-powered with a compliance of 10 VDC.

Notice Concerning Supply Systems

Because these gas mixers operate by intermittently filling a surge tank in the gas mixer, the gas mixer will demand the supply gases at full gas mixer capacity for some period of time, even if the mixed gas demand is small. For this reason, bulk gas supply systems (not portable liquid cylinders) should be used for the major gas, and in some circumstances, the minor gas. Please contact the Thermco sales engineer for guidance.


Improper use of this product can cause death, serious injury, or property damage. Personnel dealing with this equipment should read and understand warning labels and instruction manuals provided by Thermco. Only personnel familiar with industrial gases should attempt to install or service this equipment. Gases from high pressure cylinders must be reduced to the specified pressure before entering the gas mixing system to prevent the possibility of equipment damage and personal injury.

Use only oxygen in gas mixers specifically designed for oxygen service. Gas mixers not designed for oxygen service cannot be converted to oxygen service.

Flammable or corrosive gases should not enter these gas mixing systems.


Each gas mixer is supplied with one instruction manual which includes complete wiring and flow diagrams. A complete data sheet is prepared for each gas mixer specifying major parts of the gas mixer, operating pressure settings and recommended spare parts. A copy of the instruction manual is kept on file at Thermco, and engineering assistance is provided if required. Thermco has been providing service on gas mixers since 1964.

Ordering Information

Thermco gas mixers are available through many local industrial gas suppliers. Thermco gas mixers may also be ordered directly from the factory. To get a quote, click here. It is specially important to order the correct pressure conditions for the application. If there are questions, please contact the Thermco sales engineer.