Q. "I own a 3" PVC ball valve that has always been very difficult to turn. Is your brand easier to turn?"
A. Of course, we don't know since we don't know what brand we are comparing, but we will say that our larger (2 1/2" and larger) ball valves are very hard to turn. We have found this to be true with all plastic ball valves of all manufacturers that we have seen. Regardless of how difficult to turn your valve is, absolutely do not spray silicone or any other lubricant onto the ball. Most lubricants will harm the ball and will not help the plastic ball valve to turn easier. We have found that most silicones will actually damage the plastic. If all else fails and you can't "live with" how hard it is to turn your large ball valve, try Super Lube. Never use grease, faucet grease or any lubricant not specifically designed for plastics. Our larger brass ball valves are also very hard to turn. When you first get your large valve, you will note how hard it is to turn. Once it is installed on pipe and has water (clean water only) in it, you will find that it will be somewhat easier to turn. But large plastic ball valves are simply not easy to turn.
This is consistent with my experience on excessive silicone causing plastics to grind and get damaged. I was recommended to use silicone at a hardware store (asked for rubber and plastics use), and turns out it doesn't quite work well for many applications.
Enter paintball. Markers are built for easy maintenance, and use their own kind of lube: DOW Molykote 33. The parts being lubed are O-rings on metal/aluminum tubes and have to handle some 120 to 190 PSI of compressed air or CO2. The stuff is expensive, especially when companies take it, rebrand it, and add their markup to it.
I need to look more into it. Based on what I can tell now, silicone works for O-rings, but the spray stuff we commonly use is not good for ball valves and any plastic-on-plastic action.
Perhaps I'll drop some cash on the 33 stuff, both for paintball marker maintenance and for experimentation on water blasters. In particular, I'm curious on how well it works on PVC and other plastic ball valves.