Hi tmox,
It sounds like you have a very interesting project. I have developed several multi-cylinder lifting systems (synchronous-lifting) for a variety of industries, and the problems I encountered are identical to those you have described. I have seen several lifting-system applications that attempted to accomplish the task by tying all the lifting cylinders together to a single valve. The consistent problem with this approach (as you’ve already realized), is that unless the center of gravity of the load sits directly at the geometric center of the lifting stations, the cylinders will “see” different load values. Because the cylinders are driven from a single valve, they all see the same pressure, and thus have the same lifting force. Attempting to raise or lower an “unbalanced” load like this will result in the lightest-loaded cylinder moving the fastest, and the heaviest loaded cylinder moving the slowest. Not good if you are trying to lift something and position it accurately. This approach may well be workable for lighter load applications that do not require a high degree of positional accuracy. However, I have had to develop lifting systems capable of lifting several tons with an accuracy tolerance of +/- 1 mm between cylinders, and the single valve theory just would not cut it. The only method that I’ve found to provide absolute robust operation of a multi-cylinder lifting/positioning system is to use position sensing of each cylinder and feed that information back to a microcontroller. The controller in turn operates a single valve per cylinder, servoing on the position of each cylinder from a datum reference. In this manner, each cylinder is independent of the other cylinders; changes in system pressure; or lifting load changes as the load may shift during the lift sequence. If your lifting application is a dedicated system (i.e. you’re always going to be lifting the same thing to the same position), then the single valve or mechanical balance system might work. However if your application will encounter varying loads with different weight distributions, then a “semi-intelligent” lifting system may be the only practical solution. To answer your initial question of the “best (cheapest) way to ensure simultaneous operation of 4 separate pneumatic components” is usually an engineering contradiction in terms. We are always searching for the “best” and most cost-effective solution, but those two guys rarely play well together. You can have the “best” OR you can have the “cheapest”, but trying to get both really makes our profession interesting. Best of luck with your project!