Drive a 9V latching solenoid valve with 5V pulse
Just because it seems to work with 5V on the bench doesn't mean that it will work reliably (or at all) in the operating environment. You should look up the specs of your solenoid to get its operating voltage range (eg. 6.5 - 12V). If it doesn't have a minimum voltage specification then you must assume that it requires 9V. 

If you don't follow the specifications then it's your fault if it misbehaves. And any damage caused by it not operating properly will be your fault too. Why take the risk? Perhaps you only have 5V and are hoping it will be enough. Don't do that. Do the job properly and provide the solenoid with the voltage it is designed to work with.