Gas Mixer Model: 8520

Primary Applications: Welding Shield Gas, Plasma Welding, Plasma Cutting

  • Two gas mixture is set at the factory to the user specified setting, with one of the gases hydrogen. The mixture may be changed by the user to a new mixture with the assistance of a gas analyzer
  • Surge tank design will produce a highly accurate mixture from zero flow to full flow, no minimum flow rate requirement to maintain accuracy
  • Electrical circuit shuts off the hydrogen into the gas mixer if the argon inlet pressure is insufficient to create a proper mixture
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Model 8520
Common Mixtures
2% hydrogen, 98% argon
5% hydrogen, 95% argon
35% hydrogen, 65% argon
Note: Mixtures are adjusted at the factory to the requested mixture. Mixtures may be changed in the field with the use of a gas analyzer.
Mixed Gas Flow Capacity 0-500 scfh (0-13 Nm3/h)
Gas Mixing Accuracy
±0.35% of the minor component absolute for components from 0 to 7%. For mixtures greater than 7%, consult the factory. Example: For a 5% H2, 95% Ar mixture, the mixture will be within the limits of 4.65% to 5.35% H2.
Accuracies assume that the gases entering the gas mixer are at equal temperatures and the supply gases and gas mixer environment are in the range of 50°F-90°F (10°C-32°C). Accuracy outside these temperature limits will vary; consult the factory for details.
Ambient and Supply Gas Temperature Range 32°F to 104°F (0°C to 40°C)
Standard Supply Gas Pressure 100-125 psig (6.9-8.6 barg) Supply pressures do not have to be equal.
Standard Mixture Outlet Pressure 10-50 psig (0.7-3.4 barg) Regulator provided by Thermco in gas mixer for mixture outlet pressure adjustment. Note: Gas mixers are frequently engineered for non-standard pressure conditions.
Gas Connections ½ inch NPT female pipe for argon, hydrogen and mixed gas.
Surge Tank 5 gallon, ASME coded and CRN registered, pressure relief valve provided
Surge Tank Pressure Switch Solid-state sensing and output, rated 100,000,000 cycles
Power Requirements 115 VAC, 50/60 Hz, 0.5 amp. Available on request, 220 VAC, 50/60 Hz, 0.25 amps.
Electrical Construction Meets the National Electric Code for a hazardous area, classified as Class I, Division 2, Group B.
Weight 80 lbs. (36 kg)
Dimensions 31.8 in (81 cm) height, 27.3 in (69 cm) width, 10.3 in (26 cm) depth
Enclosure Steel material, with door gasket for protection from dust. The door is provided with a latch and hasp. This enclosure is not designed for outdoor installation.
Mounting Type Wall or bench indoors

Additional Information


The model 8520 is designed to mix hydrogen and argon for welding and cutting applications. These include shielding gas for plasma arc welding (PAW) and gas tungsten arc welding (GTAW). A typical example is plasma arc welding of stainless steel tubing in a tube mill.

Because the gas mixer uses a surge tank design, this type of system is ideal for applications that require maintaining a precise proportion from zero flow to full flow with high reliability. The 8520 is suitable for continuous flow or intermittent flow demand.

The model 8520 may be used to mix hydrogen and nitrogen for some applications. The 8520 cannot be used to mix hydrogen and nitrogen for furnace applications since this application requires safety controls per the NFPA 86 standard. Consult Thermco for the suitability of the 8520 for H2/N2 mixing applications.

Thermco Surge Tank System

All Thermco gas mixers use a surge tank. The Thermco surge tank system has the significant advantage of maintaining the accuracy of the gas mixture from zero to full rated flow rate. There is no “minimum” flow rate. Gas mixing systems without a surge tank will have a minimum flow rate below which the gas mixture becomes inaccurate. The Thermco surge tank system is able to accomplish this accuracy without complex control valves or flowmeters.

Safety Shutoff Feature

The model 8520 is equipped with a pressure switch to automatically shutoff the hydrogen in the event that the argon supply is insufficient to create a proper mixture. A light on the front door indicates the shutoff condition. Valving is built into the gas mixer to allow testing of this safety circuit.

Standard Supply Gas Pressure

Gas mixers will be made for supply pressures of 100-125 psig (6.9-8.6 barg) and mixed gas output pressures of 10-50 psig (0.7-3.4 barg) unless ordered otherwise. Gas mixers are often made to special pressure conditions; consult Thermco for details.


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


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 are under pressure and therefore the hazards associated with pressurized systems exist. 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.

Some gases used in this equipment are flammable and therefore constitute a fire and explosion hazard.

Oxygen, toxic, liquid or corrosive gases should not enter these gas mixing systems.

The Model 8520 can not be used for the creation of furnace atmospheres; special gas mixers are available from Thermco for that application. The Model 8520 is intended for welding applications; the buyer should consult with Thermco before applying the Model 8520 to non-welding applications.

Ordering Information

Thermco gas mixers are available through many local industrial gas suppliers. Thermco gas mixers may also be ordered directly from the factory. It is especially important to order the correct pressure conditions for the application. If there are questions, please contact the Thermco Sales Engineer.