Much like modern synthetic two stroke oils, these LPG valve saver lubricants are designed specifically to be combustible without generating their own carbon deposits in an internal combustion engine. Introducing a light oil seems counterintuitive, but it's full of detergents so it works well, think Red-X "Upper Cylinder Lubricant" if you remember that stuff? Mix it 50/50 with methanol and it works even better at dissolving and removing oily deposits
BTW, don't confuse the old skool Red-X "Upper Cylinder Lubricant" with the new generation of Red-X branded fuel treatments, they are very different products that work in completely different ways. The original Red-X "Upper Cylinder Lubricant" hasn't been available for years because despite being very effective at removing carbon deposits, it's not very environmentally friendly. Because these LPG valve saver fluids are essentially the same stuff as the old skool Red-X "Upper Cylinder Lubricant" it's not something you'd want to be introducing into the engine on MoT day as you'll probably fail the emissions test, I also couldn't vouch for the long term effects LPG valve saver fluid will have on your catalytic converter, but I'd make that same caveat about a water/meth injection kit.
At the end of the day this valve gumming issue only exists with direct injection, on port injected engines we never experience the problem because there's always fuel washing (and cooling) the back of the valve. Once the direct injection valve gumming issue was identified many manufacturers solved the problem simply by adding a second set of injectors in the inlet manifold, the engine effectively became both direct and port injected.
An LPG valve saver kit is solving the problem in the exact same way, it's just a crude port injection system that's simply relying on the depression in the inlet manifold to draw the fluid into the engine. Keep in mind these LPG valve saver kits are well proven over millions of miles on LPG converted engines that would otherwise burn their valve seats out in no time at all, and you don't need something super sophisticated to do the job.
Unlike in the LPG valve saver application, I actually don't think you’d need to inject the valve saver fluid all the time for it to clean the back of the valves, so one fill could (potentially) last a lot longer than I’ve quoted above.
Accurate metering is of course essential
