I gave this answer in a different post:
German words with origins in other languages like French and English or words with Latin origins are pronounced with a 'v' sound. All other German words have the 'f' pronunciation for the 'v'.
Loan "v-words" with 'v' pronunciation:
Visum, visuell, Motivation, Vase, Virus, Volleyball
German "v-words" with 'f' pronunciation:
Vater, Vogel, von, vor, brav, Versicherung, verwenden, vier