When designing pneumatic circuits, there are usually various ways to achieve your desired end goals. Some designs can be complex with many parts to consider, while other designs can be relatively simple; both can give you similar end results. I’d like to explore some options for designing a “2-Pressure-Select” pneumatic circuit. This type of circuit is typically used on an actuator when you need to quickly switch from a higher pressure to a lower pressure (or vice-versa) while moving in the same direction.
A good customer recently needed a “2-Pressure-Select” pneumatic circuit solution for a machine design. They rebuild and service other OEM’s automatic Bliss box and tray forming machines, and typically make improvements to problem areas when they do a rebuild. Let’s look at a few ways this 2-Pressure-Select circuit could have been done and the simple solution that solved his problem.
On each machine cycle, a vacuum fixture grabs a single cardboard blank from a stack in an upper holding area. It then retracts and drops it down a guide into the machine. Some machines also have side cardboard blanks that are dropped to form the sidewalls. Next, a horizontal mandrel is driven into the box blank, which pushes it into a fixture that automatically glues, folds, and forms the sides of the box. While the mandrel is still extended inside the box, a pneumatic slide with tooling plate is extended on each side of the box. This is where our customer needs the 2-Pressure-Select circuit.
The higher 70-psi air is needed on the pneumatic slide’s extend stroke to force the side flaps against the glued areas. The slides then need to quickly drop their air pressure to around 50-psi while still extended. This allows the slides to decompress slightly so the mandrel can be retracted out of the box, while the slides continue to apply force to the side glued areas. All of this happens in about 2 seconds! The customer was already using a 4-station air valve manifold on the machine, with (3) 4-way-2-position-single solenoid valves, and (1) blank station.
By using some internal port-gallery blocking disks, adding another (2-station) valve manifold base with a single 4-way valve and a blanking plate, and adding both an inline pressure regulator and an inline high-relief precision regulator, we could achieve a 2-Pressure-Select circuit with some creative plumbing. This solution would have complicated plumbing, causing the manifold to grow longer in size by 2 additional valve stations, added some internal blocking disks that would not be apparent to future maintenance technicians working on the manifold, and costing an additional $410 to the current manifold. This was not an ideal solution.
This option would use the customer’s existing manifold and would require adding an internal P-Port blocking disk between Stations 3 and 4 to isolate the supply air to the manifold. It would also require removing the Station-4 blanking plate and adding another 4-way valve, along with adding an inline proportional pressure regulator and control cable. This option was cleaner but would require electrical programming of the regulator. The customer would also have to find an ideal place to mount the proportional regulator and cable so it wouldn’t get damaged. Most importantly, it would add an additional $571 to the current cost. The additional electrical programming for the proportional regulator was not appealing because of concern that their customer’s maintenance technicians wouldn’t be able to service it.
This option was our best “2-Pressure-Select” circuit option. It required adding a Numatics “RT-style” 2-Pressure-Select Sandwich Regulator under the existing valve on Station-3 and plugging Port-4 of the same valve. This valve would no longer be used to control the extension and retraction of the slides, but would just be used to select the two different pressures. By energizing or de-energizing the coil, you would either get 70-psi or 50-psi air pressure out of Port-2.
On Station-4, the original blank station plate was removed and replaced with another 4-way-2-position valve, with a Sandwich Pressure Block underneath it. By piping air tubing from Port-2 on valve Station-3 to the Sandwich Pressure Block on Station-4, we now had the ability to choose between two pressures using Valve-3 and extending or retracting the slides using Valve-4.
The cost of adding the RT-sandwich regulator, the Sandwich Pressure Block, the new valve, and a few additional fittings was only $278. This was by far the cleanest and least expensive option while adding no additional length to the manifold or much electrical complexity.
Our customer needed to use a “2-Pressure-Select” circuit on their machine, so we presented him with several options that were all viable. By explaining these solutions and helping guide him on the pros and cons of each, he was satisfied with the simplest and least expensive option. This made the most sense and required the least amount of re-work to his existing pneumatic circuit.