[FotoPlasma]

If I understand this correctly, you're afraid of "backdriving" a pneumatic actuator, when it's been previously energized?

To my knowledge, you don't have to connect the exhaust ports to anything, including a one-way flow valve (I'm not too learned in the terminology, quite yet).

And, if it didn't come in the kit, and wasn't one of the three custom actuators your team ordered, you can't use it in the pneumatic system for your robot.