The only exception is with the addition of the conjunctive "vav" prefix, meaning "and". Before vet/bet, mem, fey/pey, or a sheva (I call it "Boom-off" to remember or בומ"פ) the vav becomes vowel shureq (dagesh beside the vav: says "OOOO") This is the ONLY time a Hebrew word will start with a vowel "letter" sound.
Therefore, other Hebrew words that require a vowel sound at the beginning will be spelled with one of the "silent" consonants: aleph or ayin. Some examples would be: אדם adam, (Adam, ground) or עין ayin (eye).
Confusion may occur with the vav, since it may have the consonant sound "v", OR long "OH" (when there is a dot over it) OR long "OO" (when there is a dot to the left of it). If you simply remember CVCV pattern, AND that ONE consonant CANNOT have TWO vowels assigned to it, it should clear up the confusion regarding pronunciation of the vav.
Here is vav with "OH" sound:
shaLOHM. שָׁלוֹם (peace, hello, goodbye) remember: CVC pattern! C: shin V: qamets C: lamed V: cholem vav (OH) C: mem sofeet
Here is vav with "OO" sound:
chaTOOL. חָתוּל (cat) remember CVC pattern! C: chet V: qamets C: tav V: shureq vav (OO) C: lamed
Now the "tricky" vav as a consonant. Remember, one consonant CANNOT have TWO vowels!
tikVAH תִּקְוָה (hope) C: tav V: chireq C: qof V: sheva (closes the first syllable) C: vav V: qamets C hey (although technically, I believe the combination qamets-hey is a vowel in itself, commonly used at the end of words)
mitsVAH מִצְוָה (commandment) C: mem V: chireq C: tsadi V: sheva (closes the first syllable) C: vav V: qamets-hey
The SUPER tricky ones are where, for grammatical reasons, the vav has a dagesh chazak (doubling dot) which looks just like the shureq vowel!!! The CVC rule still holds!
tseeVAH צִוָּה (he commanded) C: tsadi V: chireq C vav V: qamets-hey
yeevahLEYD יִוָּלֵד (he will be born) C: yod V chireq C: vav (with dagesh) V qamets C: lamed V tsere C: dalet This verb I found in chapter 26 of First Hebrew Primer.
Basically, if you see a vav with a dot (which usually is a shureq, or "OO"), yet the vav has ANOTHER VOWEL attached, use the OTHER vowel, and know that the extra dot is a "doubling" of the consonant "v" sound. There can be ONLY ONE vowel per consonant.
As far as the final example, of the vav with a dagesh chazak and another vowel, a common example is the name of Eve, ("Chava" in the Hebrew): חַוָּה
Can you find other examples in the Bible? Please put them in comments below! Todah!