Gas Mixer Model: 8115

Primary Application: Welding Shield Gas

  • Three gas mixture is set at the factory to the user specified setting
  • 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
  • Option of the pressure alarm system
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Model 8115
Gases Mixed
Three gases that are non-flammable and non-corrosive with one gas being oxygen.
Mixed Gas Flow Capacity 0-2,000 scfh (0-54 Nm3/h)
Gas Mixing Accuracy
For minor gas concentration >7%: ±5% of the nominal
For minor gas concentration 1% to 7%: ±0.35% absolute.
For minor gas concentration <1%: Consult Thermco.
Accuracies assume ambient and supply gas temperatures are in the range of 50°F to 90°F (10° to 32°C) and supply gas temperatures are equal.
Ambient and Supply Gas Temperature Range 32°F to 100°F (0°C to 38°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 1 inch female NPT all ports.
Surge Tank 30 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.
Weight 170 lbs. (77 kg)
Dimensions 32.0 in (81 cm) height, 45.0 in (114 cm) width, 23.5 in (60 cm) depth
Mounting Type Floor mounted

Additional Information


The model 8115 gas mixer is designed to create a constant proportion of three non-flammable, non-corrosive gases. A common application is shield gas for welding.

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 8115 is suitable for continuous flow or intermittent flow demand.

The model 8115 is designed for indoor installation.

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.

Optional Pressure Alarm System

A pressure alarm system is available to alert personnel of low input gas pressure. When one of the input gas pressures falls too low to create an accurate mixture, a light specific to the low-pressure gas is illuminated on the front door, and a horn on the enclosure sounds. The operator can silence the horn with a horn silence button on the the front door. This alarm will help prevent the creation of an improper mixture if one gas source is exhausted, or low input pressure is caused by some other reason.

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.


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.

Only use oxygen in gas mixers specifically designed for oxygen service. Gas mixers not designed for oxygen service cannot be converted to oxygen service.

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


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.

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.