Pulis says 27-year-old Hennessey has joined as understudy to Julian Speroni.
He said: "What we had a Stoke was ideal. We brought Begovic in as a younger goalkeeper to Sorenson and eventually took over from Sorenson.
"And then we went out and got another younger keeper in (Jack) Butland, so we had three different ages, but all top goalkeepers.
"He (Speroni)is getting to an age now, he's in his mid-30s, where we needed a top young goalkeeper and I think Wayne will prove to be that."
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