H2/N2, H2/Ar GAS MIXING SYSTEMS
Models 8300, 8350, 8400, 8450, 8600
Download Specification Sheet ss114.pdfApplication
Furnace Atmosphere
Mixtures of hydrogen and nitrogen are often required in the heat treating industry to create a special atmosphere in furnaces. The Thermco gas mixer can create gas mixtures from bulk sources to create a system that is economical and reliable. The Thermco surge tank based system has infinite flowrate turndown capability able to supply a single furnace or a multiple number of furnaces. Some of the common processes used with the gas mixer are:- Annealing steel coils
- Annealing copper, brass
- Brazing
- Glass metal seals
- Oxide coating of steel
- Sintering
Welding Gas
Gas mixers are available for mixing hydrogen and argon for welding purposes (usually plasma welding). The typical range of these gas mixers is 0-10% H2 in Ar, which can produce a mixture of 5% H2/95% Ar. The H2/Ar gas mixers are designed the same as the furnace atmosphere gas mixers, except the argon flow is shut off during a power failure and manual reset is not required to restart hydrogen flow after an alarm.Principles of Operation
Within the gas mixer, the major and minor gas streams are regulated to the same pressure. Downstream of the regulators, the major gas flows through a fixed orifice, and the minor gas flows through a metering valve which acts as an adjustable orifice. The two gas streams are mixed together under turbulent flow conditions and fed into a surge tank. Once the pressure in the surge tank reaches the upper setpoint on a pressure switch, the gas supplies are automatically shut off with solenoid valves. As mixed gas is required the pressure in the surge tank falls until it reaches its lower setpoint. At this point, the solenoid valves are opened and the cycle repeats.The gas analyzer continuously monitors the mixture in the surge tank. If a mixture adjustment is to be made, the operator turns the minor gas metering valve accordingly, and the gas analyzer reads out the resulting mixture. Once the desired mixture is obtained, the mixing system will maintain a constant mixture ratio.
With changing mixed gas flowrate, only the cycling frequency changes; the pressure drops across the orifices remain the same, producing a consistent mixture.
This design is simple and rugged; controllers or flowmeters on the process gas are not required.
Special Designs

Special Mixing System with 1060 Gallon Surge Tank
- Larger than 10,000 SCFH flowrate
- Special materials of construction
- Gas mixing at higher or lower than standard pressures
Thermco Gas Analyzer

Gas analyzer calibrated for carbon dioxide
in argon, indoor model.
in argon, indoor model.
The gas analyzer uses a positive pressure purge to meet the explosion proofing code. Nitrogen or argon from the gas mixer is used as the purging gas.
Alarm System
The Thermco gas analyzer and the safety alarm system have been incorporated into a single unit.Furnace Atmosphere Application
Gas mixers for the furnace atmosphere application will contain the following alarms:High Hydrogen Alarm- If the hydrogen level rises above the high alarm value on the gas analyzer, the hydrogen flow will be shut off and a light and horn will be energized.Low Hydrogen Alarm- If the hydrogen level falls below the low alarm value on the gas analyzer, a light and horn will be energized.
Low Nitrogen Pressure- If the inlet nitrogen pressure falls below the minimum necessary for proper gas mixing, the hydrogen flow will be shut off and a light and horn will be energized.
Power Failure- If a power failure should occur, the hydrogen will be shut off and the nitrogen will continue to flow. A light and horn will be energized when the power resumes.
If high hydrogen, low nitrogen pressure or the power failure alarms continue for more than approximately 5 seconds, manual reset by the operator is required to restart hydrogen flow.
The gas mixing system constitutes part of a flow control system for furnace atmospheres; as such it meets the applicable sections of NFPA 86C, chapter 7. The gas mixing system should be installed in an overall system that meets NFPA 86C requirements.
Welding Gas Application
For welding applications, the alarm functions are the same, except hydrogen flow will restart without manual reset. There is no argon flow on a power failure.Remote Alarm Module

The remote alarm module may be installed up to 1000 feet from the gas mixer with the proper wiring. The remote alarm module must be mounted in an indoor, non-hazardous area.
Specifications
Flowrate | Model | Standard Ranges (Other Ranges Available) |
---|---|---|
0-2000 SCFH (0-53.6 Nm3/h) | 8300 | 0-10% Hydrogen in Nitrogen 0-20% Hydrogen in Nitrogen 0-50% Hydrogen in Nitrogen 50-80% Hydrogen in Nitrogen |
0-2000 SCFH (0-53.6 Nm3/h) | 8350 | 0-10% Hydrogen in Argon |
0-5,000 SCFH (0-134 Nm3/h) | 8400 | Same as Model 8300 |
0-5,000 SCFH (0-134 Nm3/h) | 8450 | 0-10% Hydrogen in Argon |
0-10,000 SCFH (0-268 Nm3/h) | 8600 | Same as Model 8300 |
Gas Mixing Accuracy:
- ± 3.0% of full range over 50° F to 90° F (10° C to 32° C) temperature range
- ± 5.0% of full range over 10° F to 104° F (-12° 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.
The gas analyzer accuracy is separate. Contact the Thermco sales engineer for details.
Flow Capacity:
Rated capacity of 0-2000, 0-5000, and 0-10,000 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 0-20% Hydrogen in Nitrogen has a midrange setting of 10% Hydrogen in Nitrogen.Temperature Range - Ambient and Process Gas:
10° F to 104° F (-12° C to 40° C)Normal Supply Gas Inlet Pressure Range:
100-125 PSIG (6.9 - 8.6 barg) for major and minor gases for all models. Input pressures do not have to be equal.Input pressures do not have to be equal.
Normal Mixed Gas Outlet Pressure Range:
- 10-40 PSIG (0.7 - 2.8 barg) for models 8300, 8400, 8600.
- 10-50 PSIG (0.7 - 3.4 barg) for models 8350, 8450.
Gas Connections and Piping:
For all models the nitrogen/argon input connection is 1 inch NPT female pipe and the hydrogen input connection is 1/2 inch NPT female pipe. For all models the mixed gas connection is 1 inch NPT female pipe, except the model 8600 which has a 11/2 inch NPT female connection.Surge Tank:
30 gallon for Models 8300, 8350; 60 gallon for Models 8400, 8450; 120 gallon for model 8600; carbon steel, ASME coded, and CRN registered; pressure 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, ±10 VAC, 50/60 Hz., 0.9 Amps (220 VAC, 50/60 Hz. available on request).Electrical Construction:
The gas mixer is designed to meet the National Electric Code for a hazardous area, classified as Class 1, Division 2, Group B. No other code requirements or approvals are claimed by Thermco.Weight and Dimensions:
Model | A | B | C | Net Weight | Crated Weight* |
---|---|---|---|---|---|
8300, 8350 | 55"(140cm) | 41"(104cm) | 31"(79cm) | 282 lbs.(128 kg) | 460 lbs.(209 kg) |
8400, 8450 | 63"(160cm) | 51"(130cm) | 38"(97cm) | 400 lbs.(181 kg) | 620 lbs.(281 kg) |
8600 | 72"(183cm) | 75"(190cm) | 42"(107cm) | 655 lbs.(297 kg) | 1010 lbs.(458 kg) |
*These are crated weights for shipments to North America. Crated weights to other locations will vary.
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