Hand-held Narrow Flame Propane Weed Burner


Allen Dong, I-Tech, PO Box 413, Veneta, OR 97487

This invention was declared public domain on February 17,1997, a gift to humanity

Commercially available hand-held propane weed burners generally use lots of fuel, producing big flames to burn large areas quickly. However, some situations require smaller flames, for example, burning weeds on top of the plant rows prior to crop emergence or adjacent to plant rows after the crop emerges.

A customized, narrow flame propane weed burner can be made using a brass sprayer nozzle (Figure 1). The nozzle is adapted with a flame shield that optimizes the air-to-propane ratio, while protecting the flame from the wind. The flame shield is adjusted by trial-and-error to produce a blue or blue with orange halo flame with resistance to flame extinction when subjected to cross wind. The blue flame has the highest flame temperature, but low visibility in direct sunlight. The yellow and orange flame is an oxygen starved, low temperature flame with greater visibility in direct sunlight. Flame size, color, and stability are affected by the gas pressure (gas regulator setting) and exit velocity (orifice size at the burner head and the needle valve setting).

The optimal flame shield using a 3/4 inch copper pipe (Figure 1, item H4) on a brass sprayer nozzle ("TeeJet Cone Spray Tip"*) with 0.031 to 0.047 inch diameter orifice (TeeJet D1, D2, or D3 orifice plate) and 0.018 to 0.030 inch diameter orifice gas regulator has the following features:

Components for the narrow flame propane weed burner are described in Figure 1. The copper flame shield is pressed on the TeeJet No. 1325 cap and then soldered with silver solder. All other copper components are also soldered with silver solder. Sprayer parts are available from agricultural, fertilizer, and sprayer suppliers. Propane parts are available from camping and propane suppliers. Approximate cost is $75 (including the cost of the propane bottle).

The estimated burn time is 3 hours per gallon of propane using a 0.020-inch diameter orifice disc (TeeJet 4916-20) as gas regulator and one burner head with a 0.041-inch orifice disc (TeeJet D2).

A larger flame requires a larger flame shield with more air intake ports. This can be made using a reducing coupler, 1 to 3/14 inch copper x copper, and a 1 inch diameter x 2 inch long copper tube, type L (0.046 inch wall). Five 5/16-inch air intake holes are drilled on the shoulder of the reducing coupler, and sixteen 1/4-inch holes are drilled in the last 1 1/4 inch of the 1 inch copper tube. Use 0.047 to 0.063 inch orifice discs (TeeJet D3 or D4) at the burner head.
 
 

Figure 1. Narrow flame propane weed burner with 2 burner heads.

A Propane bottle, 1 gallon

B POL connector, ¼ inch male pipe thread, preferably with a

Restricted inlet hole, 0.018 to 0.030 inch diameter

C Gas regulator (omit C1 to C3 if POL connector is restricted)

C1 TeeJet 4676 adapter, ¼ -inch brass

C2 TeeJet 4916-20 orifice disc (0.020 inch diameter)

C3 TeeJet type TT nozzle body, ¼ inch male, brass

D Propane hose, 4 feet length, ¼ -inch pipe thread, female-male

E Needle valve, ¼ inch, female-male

F Pipe bushing, ½ to ¼ inch pipe thread

G Wand made from 1/2 inch copper plumbing

G1 Two adapter, ½ inch copper x ½ female pipe thread

G2 ½ inch copper tube, 24 to 30 inch long

G3 ½ inch copper tee

G4 ½ copper street elbow

H Burner head

H1 TeeJet type TT nozzle body 1/4 inch male, brass (same as C3)

H2 Orifice disc, 0.031 to 0.047 inch diameter (TeeJet DI, D2 or D3)

H3 TeeJet No. 1325 cap, brass (can be substituted with TeeJet No.4676 cap)

H4 ¾ inch diameter x 2 ½ inch copper tube, type L (0.040 inch thick wall); four 5/16 inch diameter holes, drilled 5/8 inch on center from one end of the tube; sixteen 3/16-inch diameter holes, drilled in four sets of 4 in the last 1-inch of the tube

Use with caution. Propane is a pressurized flammable gas. All connections and solder joints must be properly sealed, without any gas leaks. Conduct initial flame tests in the shade or in low light conditions to enhance flame visibility.

Applications:

1. The propane weed burner can be used to burn weeds in the plant row prior to crop emergence. The soil surface protects the crop from flame damage, while the flame kills early emerging weeds. On a 2 row bed, the wand can be configured with 2 burner heads spaced the same width as the crop rows (Figure 1).

2. After the crop emerges, weeds adjacent to the crop row can be flamed using 2 burner heads and a tunnel shield to protect the crop (Figure 2). The two burner heads are separated 6 inch on-center and held 1 1/2 inch above the ground surface by straddling the tunnel shield that has a 1 ½ inch opening at ground level.

This configuration was field tested on 5-inch tall garlic plants. It was easier to walk backwards, pulling the burner along, rather than forwards, pushing the burner ahead. Flames can lap under the tunnel shield when the shield was dragged across uneven surfaces, especially high velocity flames. The burn time was approximately 2 hours per gallon of propane using 2 burner heads with a 0.031 inch diameter orifice discs (TeeJet D1), and a 0.018 inch diameter orifice disc as gas regulator (TeeJet 4916-18).

Figure 2. Propane weed burner with crop tunnel shield constructed from a 9 x 17 x 0.047 inch (18 gauge) sheet metal.

3. For taller crops, attach a flame shield surrounding the burner heads (Figure 3). The flame shield suspends the burner heads 2 to 2 1/2 inches above the soil surface. The two burner heads are spaced 4 inch on center, to distribute the flame. Using more than two burner heads will exceed the capacity of a one-gallon propane bottle to provide gas vapor. Installing such a flame shield to a commercial propane weed burner will improve their burn efficiency, protect the flame from cross wind, and protect the crop from the flame.

Figure 3. Propane weed burner with a flame shield. The flame shield is constructed from an 8 1/2 x 20 1/2 x 0.047 inch sheet metal.

Acknowledgements: Technical assistance from Roger J. Edberg, University of California, Santa Cruz.

* "TeeJet" products are manufactured by "Spraying System Co.", P.O. Box 7900, Wheaton, IL 60189-7900, USA. No endorsement of "TeeJet" or "Spraying Systems Co." implied.
 
 

A Propane Weed Burner for the Garden


By Allen Dong, I-Tech, PO Box 413, Veneta, OR 97487

Public Domain--a gift to humanity. October 23, 1998

A commercially available hand-held propane weed burner (BernzOmatic Outdoor Torch model JT800, Figure 1A) is modified for use in the garden. The BernzOmatic Outdoor Torch has a 1-inch diameter burner head that provides a narrow flame. A flame shield is added to the burner head (Figure 1B) to direct the heat downward and to shield the flame from the crop. With this modification, the burner can be placed within 1/2 inch from the crop and used between crop rows.

The modified burner was field tested on 3/4-inch tall broccoli. Swaths of weeds 4 1/2 inches wide and 1/2 inch away from the crop rows were flamed with no damage to the crop. It is easier to walk backwards, pulling the burner along, rather than forward, pushing the burner ahead. Flames can lap under the shield when the shield is dragged across uneven surfaces. The burn time is approximately 6 hours per gallon of propane. Propane is a flammable gas, use with caution.
 
 

Materials:

Construction:

Cut and fold the sheet metal as shown in Figure 2. Secure the four folded corners with sheet metal screws. Insert a hose clamp through the two slots on the center tab and attach the flame shield to the burner wand. Insert the steel support wire through the hole at edge of sheet metal, 1/2 inch in, and bend the wire 270 degrees to secure it. Attach other end of the wire to the burner wand using a hose clamp.
 

Figure 1: A) BernzOmatic Outdoor Torch, B) Torch with flame shield.
 
 


 

Figure 2: A) Sheet metal, 6½ x 14 inches, B) Sheet metal folded into a flame shield.
 
 

Note: Mention of product name and store name does not imply endorsement by I-Tech.