There are, as I understand, three "schools":
1 - vav is always [v], also in words like השתחוו ,ופוה, ייקוו
2 - vav is [v] except AFTER u, e.g. in ופוה, where it is [w]
3 - vav is [v], except BEFORE AND AFTER u, so in ייקוו, ופוה, השתחוו it is [w].
(Words like רוח, נוח are a different matter - here the (unwritten) glide is always [w])
Which "school" do you follow on this website?
From what I've heard - and seen in G. Khan's book -, you probably follow school 1 or 2, I'm referring to ייקוו [jiqqɑ:'vu:].
The variation in the Middle Ages on this point is interesting. For example, according to Misha'el ben 'Uzzi'el, you would pronounce vav as [w] after pretonic [uː] (i.e., in ופוה). According to David ben Abraham al-Fāsī, on the other hand, you would pronounce it as [v] even after pretonic [uː].
On this website, we follow al-Fāsī and school 1.
For more details:
Khan. TPTBH §I.1.6, p. 176.
Khan and Kantor. forthcoming. "Waw to Vav: Greek and Aramaic Contact as an Explanation for the Development of the Labio-dental [V] from the Labio-velar [W] in Biblical Hebrew."
Correction: ייקוו. [jiqqɔ:'vu:]