The gas system is from the LPG tank to the nozzle and consists of some components I've assembled from McMaster-Carr, Home Depot and Amazon.
Moving from the tank towards the burner, first we have the regulator. The regulator is needed to reduce the pressure from inside of the LPG tank, from say 150 psi to a usable pressure like 5 or 10 psi.
My regulator is a 0-30 psi adjustable, although it doesn't have to be adjustable, as a 10 psi fixed pressure regulator would work. You can then use the ball valves to control gas rate. The regulator screws into the tank with an ACME connection. It's important to recognize there are two connections types: ACME (outside threads on the tank valve) shown in photo and P.O.L. "Prest-O-Lite" which has inside left-hand threads on the tank valve.
From the regulator we have a 1/4" NPT tee that goes off to the pressure gauge. As the tee is a female/female/female, I needed a 1/4" NPT nipple to connect the gas hose to the accelerator assembly. The hose screws into the burners with a 1/4" female NPT connection.
A single accelerator assembly consists of the following parts fitting together with gas rated pipe dope.
1 - 50785K152 Medium-Pressure Brass Threaded Pipe Fitting, 1/4 Pipe Size X 7/8" Close Nipple
2 - 4205166 Ball Valve, 1/4" F- 1/4"F, WOG 600, 150 WSP, Lead Free, Forged. ProFitter
3 - 4429K411 Brass Threaded Pipe Fitting, 1/4 M to 1/8 F Reducing Bushing
4 - 4568K115 Standard-Wall Brass Threaded Pipe Nipple, 1/8 Pipe Size X 3" Length
5 - A55 6240 Adapter, 1/4" OD to Flare 1/4" Compression with Gasket
6 - KH710 Lincoln MIG welding contact tip, 0.035".
7 - 9151K12 Nickel-Plated Brass Threaded Pipe Fitting, 1/4" Pipe Size, 90 Degree Elbow
8- 4568K139 Standard-Wall Brass Threaded Pipe Nipple, 1/4 Pipe Size X 5" Length
9 - 50785K222 Medium-Pressure Brass Threaded Pipe Fitting, 1/4 Female Female Male Tee
Substitute items whenever practical. For example I couldn't locate a regular brass elbow, but the nickel plated was available; nipples could be iron etc.
All of these connections are made with gas rated pipe dope. This helps seal the threads and makes it easier to disassemble later.
Note: You can take the handles off the ball valves and reorient them to a more useful position. Simply undo the nut rotate the handle (not the valve) and put the nut back on and tighten.
Position the torches into the burner tubes. The tubing adapters and MIG tips have to be removed to fit into the torch bracket. Leave the setscrew on the torch bracket loose. This will allow us to slide the torch in and out inside the reducer and tune the burner. Thread the nipple back onto the reducer adapter.
Once you have everything plumbed, close the ball valves, close the regulator and make the connection to the tank. Fill a squirt bottle of water and few drops of dish washing soap added. Keep this handy. Open the tank valve and squirt the regulator inlet. If no bubbles appear, open the regulator and check each connection from the regulator, to the gauge and all the way down to the ball valves. If you have some bubbles at any connection, Turn the tank valve off and tighten the connection (sometimes a 1/4 turn is all it needs) and recheck it again with soapy water.
Place or fix the burner assembly to something that won't catch on fire.
Loosen the flare setscrews. Start with them flares about 1" past the end of the 3/4" pipe.
With the regulator open, open one of the ball valves and hold a flame (BBQ lighter/propane torch) in front of the flare end. If it lights and stays roaring you are doing well. If it sputters and goes out, you'll need to adjust the position of the torch inside the bracket and/or adjust the amount of the flare is sticking out. We're looking for a strong blue flame with not too much yellow or orange tips.
Once one burner is tuned. You can shut it off by closing the ball valve and lock all the setscrews down. Set the torch and the flare positions on burner #2 to what you have setup for burner #1.
Next we'll build the body of the forge.