For those with a flaming dial (AKA: flashback), I did a little work to see whatís what.
Already replaced the piping - By way of background, last month I replaced the thinwall tube that connects from the dial to the back of the grill where the gas line attaches. That writeup and pictures are posted here: http://www.pizzamaking.com/forum/index.php/topic,26507.msg273659.html#msg273659
Testing behind the valve - A few days ago, the wind was still and I detected a slight whiff of propane when cleaning under the Blackstone. I donít like leaks, so I read up on gas valves and then took mine apart. The first picture shows the dial removed from the Blackstone. If you are wondering how much leakage is coming from your BS valve, just remove the dial and squirt some soapy water in there. The next picture shows how much leakage my valve had (cover removed for clarity). Note the bubbles just forward of the faceplate. Hopefully you are noticing that there are not a lot of bubbles. On a calm day, I could smell just a few bubbles. (At this point if you don't see a lot of bubbles, don't smell any propane, and the dial turns freely, you don't need to do anything but enjoy pizza.)
If you are wondering how I got the stainless cover plate off, I did that with the pipe replacement above. In short, I drilled out the rivets along the sides with a ľĒ drill and replaced them with SS sheet metal screws. Refer to the earlier link for details and photos.
Inside the gas valve - The next picture shows what the gas valve looks like removed from the Blackstone. Notice that I marked the alignment of various pieces with a black Sharpee to ensure everything goes back together correctly. The upper-right part of this picture shows the backside of the faceplate with one screw sticking through. The spring below goes between that center axle and the tapered brass insert. It isnít really that complicated, but when you remove the two screws on the faceplate, it also releases the valve body and the spring could fly off if you arenít paying attention. (Hint: pay attention)
Lapping a valve - The next picture shows a close-up of the gas valve put into a vise. I used a piece of flexible tubing to stuff into the tapered brass insert. The brown ooze is rubbing compound (used for buffing out a car) although you could use polishing compound, maybe even an aggressive boat wax. The materials involved in the valve are aluminum and brass, so carbide incrusted with diamonds is not necessary.
Next I put the tubing between my palms and rubbed my hands back and forth for a few minutes. This action grinds the tapered brass into the aluminum valve body and seats the valve. (If you are not familiar with lapping a valve search google images or youtube.) After a few minutes, I washed the two pieces in soapy water and blew everything clean with compressed air. I used a dab of grease between the brass and aluminum to keep things turning smoothly. Be careful with the grease. The holes in the tapered brass and the brass jet (last photo) are very small and you donít want a wad of grease gumming up the gas flow.
I reassembled the valve and put the Blackstone back together. Initially I had a few bubbles, but those quickly subsided as I moved the valve back and forth to seat it in with the spring. The valve, now lapped and greased, operates much more smoothly than before.Update:
Lapping didnít last. A few days later I smelled gas again, soaped the valve and saw bubbles. Iím at a bit of a loss for a durable fix. The best advice I can offer is to get a replacement valve from Blackstone, ideally within your 1 year warranty.
Fortunately it is easy to turn off the gas when not in use.