I could be wrong, but I think that you are talking about Dually Valves and not Dullay Valves.
If I am right, I use something very similar on my coach to make it much easier to maintain the air pressure in my inner rear tires.

I use a valve stem extension on the inner wheel and a support bushing in the outer wheel to support the lengthened inner valve. The extensions are available at most truck tire dealers, and the support bushing are available from the wheel manufacturer or from some large truck tire dealers. You can also buy the kit (2 bushings and 2 extensions) at most FMCA conventions for about $20.

The bushings vary in size, so measure the hole in your wheel that the valve will go through, the length that you need for the extension, and it also helps if you know if the wheel was made by Alcoa or Accuride. But be sure to get the needed bushing, because the unsupported extension can cause a leak.

Gerald

You may have heard about a lot of issues with solid extensions, but now you can hear some good.  I have used the same 2 brass extensions on the rear inside duals on 2 different coaches over the last 11 years without a leak.  I bought them so long ago, I can't remember the brand, so I will call it X brand.  I purchased them from an auto parts store in Indio, CA.  To use the The Dually Valves, you will have to dismount the tire and replace the existing stem.  Your choice.

Larry

Quoted from cnlshirk

You may have heard about a lot of issues with solid extensions, but now you can hear some good.  I have used the same 2 brass extensions on the rear inside duals on 2 different coaches over the last 11 years without a leak.  I bought them so long ago, I can't remember the brand, so I will call it X brand.  I purchased them from an auto parts store in Indio, CA.  To use the The Dually Valves, you will have to dismount the tire and replace the existing stem.  Your choice.

Larry

Thirty years and a several motorhomes. I feel they seal better if you dampen the O ring with a bit (apply with a Q tip) of silicone lubricant before installing.