Sandwich regulators are designed to be used with either sub-based or manifold-based compressed air valves.
As an example, let us say we build an air valve assembly with ten 4 ported, two position valves, and each one of these valves is controlling a double acting air cylinder.
Some of those air cylinders will need the pressure to them regulated, so that we can adjust the cylinder force on the extend stroke, and also on the retract stroke.
This could be a valve / cylinder plumbing nightmare.
An in line pressure regulator installed in the line between the air valve and the cylinder is not an option, as in-line regulators are built to have unidirectional air flow. Install one in line between the valve and the cylinder and yes, it will regulate the air pressure to that end of the cylinder, but when the valve shifts and air now has to exit the line with the regulator in it, the air cannot exhaust properly as the regulator will restrict the flow.
Yes, we could install quick exhausts in each of the cylinder ports, so that the exhausting air could escape right there, and not try to flow back through the in-line regulator. That would be 20 quick exhausts we would need to plumb.
And, for our hypothetical bank of 10 air valves and 10 air cylinders, we would also have to install 20 in line regulators to achieve our goal of being able to adjust the force of the stroke of each cylinder in both the extend and retract action.
The solution is, of course, the sandwich air regulator.
The sandwich regulator package will normally include bolts long enough to travel through the air valve, through the regulator, and into the base. I suggest that you do not toss out the original bolts. They will come in handy in future should you wish to remove the regulator for any reason.
Sandwich air regulators typically have their pressure adjustment knobs at one end, and when a number of them are installed on the same valve bank, the adjusting knobs will all be at the same end, allowing quick and easy adjustment of the air pressure for each cylinder, on both the extend and retract strokes.
Accuracy of the sandwich regulators, by and large, is of the general purpose regulator variety meaning that, when working properly, they will reliably hold the pressure within a 2-5 PSI range. I suspect that you can request a higher tolerance sandwich regulator from the manufacturer, should you have the need.
Each sandwich regulator will be unique to the company that builds the regulator and the air valve into which it sandwiches. Sandwich regulators are, to the best of my knowledge, not interchangeable with other valve brands.
In the event that you have a sandwich flow control installed between the valve and the manifold or sub-base, the sandwich regulator would normally be installed between the valve and the flow control. Be extra careful installing the variety of gaskets that these assemblies will are equipped with.
When you purchase the sandwich regulator for a specific air valve brand, it should come with sufficient bolts long enough to span the valve, regulator and sandwich flow control combined, but better check to be sure! The correct bolts may be difficult to source elsewhere. Check and make sure they come with the kit.