I would think any of the "prefab" Datalogging/charting vi's should get you started. Are you intending for Labview to supply the square wave to drive your solenoid, or from a separate supply? If you're using a separate supply, it should be a snap to just sample that like any other channel. You can then compare the lag time of the air flow to the square wave. I don't imagine you're doing very high repetition rates with the valve...perhaps on the order of seconds?
Eric
Eric P. Nichols
P.O. Box 56235
North Pole, AK 99705