A piece of machinery or a fixture may have a number of different types of air-driven actuators on it, and each on of those actuators will have an air supply valve. When you have one or two actuators, installing an in line air valve for each isn’t much of a burden. However, when you have many actuators, how do you make the installation of a valve for each of them easier?
Not only do you have to concern yourself with the air supply to each valve, if the actuators are double acting, then each valve will have two air lines running to each actuator. Add in the fact that some, or all, of those air valves may be solenoid operated, and now you have to bring a power supply to each air valve too; complex and very time consuming wiring and plumbing.
The solution I would always opt for is to use a sub-based, manifold type valve configuration, with all air ports and all wiring connections made one-time into the base of the valve bank.
Even though each valve would have a solenoid or two on it to power the valve, the wiring of those solenoids would be accomplished by an electrical quick-connect that inserts into the base receiver when I attach the valve to the base.
Now, when the moving part of the valve ultimately fails, that part is the top. The top is quickly and easily removable and replaceable by a couple of screws, and there is no need to touch either the air lines or the power supply to replace a failed valve.
Sub-base valves come in a variety of shapes, sizes and Cv (flows) depending on the manufacturer. They cost a bit more up front, however, in a higher cycle, or time sensitive valve application, sub-based valves allow a valve repair in a minute or so. Two or three screws, off comes the valve, on goes the new valve, two or three screws, and your machine is back in business.
Depending on the application, sub-base valves, with their initial higher up front cost, quite likely will save a bundle in improved machine up time over the medium to long haul.