Wash the orange and make sure it is firm to the touch without any soft spots. Slice both ends off and then slice in half from end to end. *You can keep the orange whole, but it is easier to slice it when it is cut in half.
1 large navel orange
Slice the orange into ¼" slices and try to get them as even as possible.
Whisk together the sugar and the water and pour into the inner pot of your pressure cooker. Lay the orange slices in a single layer in the bottom of the pot.
½ cup granulated sugar, ½ cup water
Put the pressure lid on and turn the valve to seal. Set the pressure to high and the time to ZERO minutes. If your pressure cooker doesn't allow you to set zero minutes, then set it for 1 minute. Hit start.
Once the pot has come to pressure and either goes straight to keep warm (when zero minutes has been set) or when it starts the 1-minute countdown, immediately release the pressure and turn the pressure cooker off.
When the pressure has been released, open the lid and remove the orange slices with a slotted spoon or spatula. Place them on a dehydrator rack.
Place the rack into the dehydrator and set the temperature to 120℉/50℃ and the time for 2 hours. When the time is up, the orange slices should be just slightly tacky and pliable.
Toss them in additional granulated sugar if desired and lay them back on the rack until you plan on using them. Please see recipe notes for storage instructions if you don't plan on using them within a few hours.
Room TemperatureYou can store the orange slices at room temperature on a cooling rack for 1-2 days as long as your house is not humid.If your house is humid, the oranges will absorb the moisture from the air and can become wet and sticky if left too long. If this happens, you can pop them in the dehydrator for a short time to dry them again.You also don't want to store them in a container of sugar at room temperature because the juices from the orange will moisten the sugar and create a wet sugary mess. If this happens, you can rinse them off and dry them again and then coat with sugar.RefrigerationIf you are going to use the orange slices within 3 days, you can store them uncovered in a single layer in the refrigerator. For longer storage, I would store them in layers with parchment between the layers in an airtight container or zip lock bag.They will last at least a week in the fridge when stored properly.