Hey everyone! This is my first post on this site, and I am in a bit of a bind. The robot that I am building would operate much more consistently with two pneumatic cylinders performing identical actions on either side of my contraption. However, I only have one air compressor and one pressure gauge. We have multiple solenoids and multiple air cylinders. How would I set this up? Is it even possible to do what I am asking? Any helpful replies are much appreciated.
Use T fittings to split the lines after the primary regulator. Or use a manifold for your solenoids, it’s a bit cleaner.
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If you want the two cylinders to operate identically, then use a tee-fitting after each of the solenoid outputs.
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If you want the cylinders to operate as identically as possible (if not mechanically linked) make sure all the tubing between the reservoir and the solenoid(s) and the solenoids to the cylinders is the same length (or as close as you can get it)
If using a manifold for the solenoid(s), just worry about the distance from the manifold outputs to the cylinders.
Tldr; make the tube lengths the same after the solenoid.
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The advice you’ve gotten on making two cylinders work together is great, but there are some other things that you might need to know. First off, you actually will need two pressure gauges in the pneumatic system to be FRC legal. One must be on the high pressure (air compressor, air tank) side of the system and the other on the low/working pressure side (i.e., after the pressure regulator). What you won’t need more of is compressors, since you’re only allowed to have one on the robot in any case. You do also need several other components to make a legal system. If you haven’t seen it, there is a new official guide to pneumatics from FIRST, which covers all the basics of how to set up a system.
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You’ve received some good advice. If it doesn’t seem to make sense in terms of your setup, please post a photo of your pneumatics.
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Please note that while the official guide is a great resource and it will show you legal ways to plumb your pneumatics, it doesn’t show all the legal ways in which you might do so. For example, we like our pressure release valve to be high and very obvious, so this year, it was convenient for us to use the second tank connections to do so (we could have used only one of them and plugged the other, but this looked cooler 
).
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I’m glad you posted this. I didn’t know the pressure relief needed to be hard connection only into the compressor.
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I’ll just add here that the solenoid has a maximum flow rate, so if you are moving large volume cylinders and split the output after the solenoid, that flow rate will be split between the two cylinders and each will extend about half as fast. If you need to extend two large cylinders quickly, you should use two solenoids with the T connectors before the solenoid input, and make sure in code you’re switching both solenoids at the same time (or plug them both into the same ports on the PCM/PH depending on how much current they draw).
If said find yourself with a design such that said cylinders are going to be actuated multiple times during a match, please remember that the FRC-allowed compressor (legally 1.1 cfm max) is pretty weak. The actual Viair compressor makes only about 1/4 of that, see chart at https://www.andymark.com/products/air-compressor) – so, during a 2.5 minute match, you have whatever air you start with in your air tanks (0.02 cu ft) and the limited amount the compressor can wheeze out – you should definitely do the calculations to insure you have adequate supply and pressure through the match. Although Andymark recommends no more than 6 air tanks, I have seen a robot with twice that.