Plywood is made of three or more thin layers of wood bonded together with an adhesive. Each layer of wood, or ply, is usually oriented with its grain running at right angles to the adjacent layer in order to reduce the shrinkage and improve the strength of the finished piece.
Ok this is technical stuff but since the plys are laid up by rotating each layer 90 deg, what you end up with is a panel that is just as strong in tension as it is in compression. Therefore, the direction the plywood is installed does not affect it's strength, which is one (along with reduced movement) of the key assets of plywood.
and also is Fulterer a good brand? sorry for all the questions just I know nothing about drawer slides.
I have no experience with the brand (at least that I can remember). But I have used off brands (even ones sold at home depot ) without any problems. I understand your desire to fully investigate a product you are unfamiliar with but you should be aware that relying on a forum like this is no substitute for direct experience. People's standards vary and in the end it is you that must stand behind the work that you produce. Claiming to the client that the guys over at the 207 said it would work won't help if something fails
. I would recommend you purchase a couple of samples that have a similar spec (one a brand name and another a off brand) and do your own examination and make your own determination on which one to use.
I want to again emphasize the size and proportion issue. I have used deep drawers up to 36" but the drawers are narrow (12" to 16" 'filing cabinets' type drawers). The double decked slides (I don't know another term for them) is a typical design in order to provide the strength to support the cantilevered weight (again a technical strength of materials, statics and cost of manufacturing issue). Why this design is the way it is I have never investigated.
One final note, I could be wrong, but based on the type of questions, it appears that you may be starting your inquires at the forum and not doing some basic research first and then coming here to ask for guidance when you can't find the answers. It is essential that you develop the ability to do basic research on products and technical issues. There will be times when no one is available to help so ultimately you have to develop confidence in your own abilities to sort through these issues. In my opinion a forum like this is best used as a check against your own research to make sure your didn't miss something or get accidentally off track. No matter how deep or broad the knowledge base of the members are they will never be as comprehensive as what is available online and through product support services.