The button switch valve method is not always a good idea, be aware that during the period you select up retracts and the the moment the button valve is triggered, there is no air pressure holding the door open, if your model is one such that the airstream will close or move the gear door with no air pressure, you risk the door getting caugth on the rising strut and then have a failed retraction...it works for the F-16 ( I used the method) but not on every model.