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Converting an M1937 Fire Unit to Propane
Flame and Pressure Control (Part 6)

By David Jarvela

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The next problem I encountered was the control of the gas to the burner. Bob told me he just used a needle valve with a direct connection to the propane tank. I knew the problem with that would be that high pressure from the tank would be at the valve and it would change with temperature conditions so control would be almost impossible. 

The converted propane M1937 fire unit
The converted propane M1937 fire unit showing the hose and propane tank.

After much experimentation with both high and low pressure regulators and different size orifices I settled on a Model 350 regulator made by Marshall Gas Controls. It will regulate from 0 to 26 pounds per square inch (PSI). The burners appear to function best by turning the regulator wide open and backing off just a bit. The control with the needle valve is very finite within the first couple turns of the knob. 

I might add I tried another high-pressure regulator rated to 30 PSI, which set me back more than $30.00. It functioned no better than the Model 350, which was only $16.00. I had my propane dealer make up a ten-foot hose with fittings to attach to the regulator and to run to the needle valve.

The hose cost $13.00 and the 3/8" male npt x 1/4" inverted flare adapter for the hose to attach to the needle valve was $1.50. The needle valve was $12.90. Assemble the adapter to the needle valve using pipe dope on the 3/8" male threads. Do not apply pipe dope on the 1/4" inverted flare end. 

Remember to hold the needle valve with the adjustable wrench when you tighten the adapter fitting with the other wrench. Then attach the inverted flare fitting on the hose your propane dealer has assembled for you to the adapter. Again, do not use pipe dope on these connections. The other end of the hose will connect to the regulator using male threads that require pipe dope. The POL fitting will come with the regulator. That is the fitting that screws into the propane tank.

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  1. Converting an M1937 Fire Unit to Propane

  2. Fire Unit Conversion

  3. BTU Rating of the Burners

  4. Supplies and Tools

  5. Conversion Procedure

  6. Flame and Pressure Control

  7. Safety Tests

  8. Cooking with the propane burners

David Jarvela is a native of White Pine, Mich. He currently lives in Hoyt Lakes, Minn. Questions or comments? E-mail him at:

Copyright 2000 by David Jarvela. All rights reserved. Used with permission.

October 2000

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