Recently in working with my student we came across the word <valuable>, I am finding myself questioning that we replace the final <e> and replace it with the vowel suffix <-able>.  

I write the word sum:

<valu/e> + <-able> --> valuable

I am questioning replacing the <e> because I am seeing it as part of a vowel digraph and I would not think it possible to remove part of it. 

I have asked the following questions:

is the <e> a single non syllabic <e> ?  Possibly because I believe English words do not end in <u> therefore <e> is there to prevent that final <u>

In that case, are we able to take the letter <e> away?