Dynamic fields layout based on categories
So I'm going to add this as an answer just in case others find it a useful option to pursue. 

I would create your fields; voltage, flow rate, etc. then I would create a Structure called Products with different Entry Types corresponding to the various categories you are using to sort your products. Then you can add your fields to the appropriate Entry Types. Then when you go to add a new product, you'll have a dropdown where you can select what Entry Type this entry should be. 

That's how I would setup your site structure if I were in your place