[Roboman01]

The valve in the schematic above is a 5-port, 4-way, 3-position valve with the center position blocking both pressure and exhaust ports. This allows the pneumatic cylinder to be controlled similarly to a hydraulic ram, since one can shut off and trap the air inside the cylinder, preventing significant movement.

Of course, <R73> specifically states that this is not allowed, so one must be able to vent the trapped pressure at the same time as the rest of the system, from a single valve. The two check valves allow this. Each check valve allows air to flow (mostly) unobstructed out of the supply to each cylinder, but does not allow the high-pressure air to reach the cylinder supply lines. Since the pressure in the cylinder is lower than that of the accumulator, little air will be lost, due to the natural tendency for the higher pressure air to seal off the check valve.

During normal operation, this will cause the cylinder to act as if it were connected via a normal piece of tubing. However, in the event that we need to vent all of our stored pressure rapidly, the check valve will allow the stored pressure in the cylinder to flow straight out the dump valve.