Since both the air and wood gas come into the engine through the same opening there needs to be some way to get a proper mix. This is done with a valve, an old engine carburator or a ball valve. The first engine I used a carburetor as can be seen in the pictures below. I didn't have another one and didn't want to pay for a new ball valve. I figured I could just make something cheaply. It didn't need to be as tight as a carburetor butterfly valve. It did need to stay put once moved. It needed to fit 1" steel or PVC pipe. I wanted it possible to disassemble and not be welded in place. No welding would be best since I don't have a welder. Any purchased parts needed to cost much less than just buying a valve. The pictures below show what I came up with.
A 1" steel or PVC pipe is drilled through the center using a 1/8" drill bit and a doweling jig designed for wood. Getting the hole right in the center helps a lot in making a good valve.
A disc cut out of aluminum flashing using a tin snips. The size is just a bit larger than a quarter.
I purchased 2" by 1/8" cotter pins for 23 cents each. These are used to hold the disc.
The disc is placed between the two legs of the cotter pin and centered. A line is drawn on either side of the cotter pin on the disc. The disc is bent on each of the line at a 45 degree angle in opposite directions. This forms a slot for the cotter pin and keeps the disc from falling out.
With the disc held in place with a needle nosed pliers then slide the cotter pin through the 1/8" hole in the pipe.
Check the fit and movement of the disc.
The eye of the cotter pins I was using were just a bit smalled than a 10 32 machine screw. I tapped the eye and screwed in a 10-32 screw adding nuts on both sides.
A spring was added to put some tension of the cotter pin. The ones I used were leftovers from a facet repair kit for the kitchen sink.
Lastly put a bit of pressure on the head of the cotter pin and spread the ends of the cotter pin apart.
A PVC version of this value was added between the air cleaner and the gray plastic box on the generator.
The two steel ones are for a future Simple-Fire charcoal gasifier.