Taylor Marshall, himself a former Episcopalian minister, writes about the vallidity of Anglican orders on his blog. He's answering a quesation he received after talking to Marcus Grodi on EWTN's The Journey Home: Does the Anglican Church have a valid Eucharist?
Dr. Marshall has a short answer (No.) and a longer explanation.
To quote: Here's the short answer: No, Anglicans or Episcopalians (the tradition deriving from Henry VIII's Church of England) do not have a valid Eucharist. This question was settled by His Holiness Pope Leo XIII in his papal bull Apostolicae Curae on the nullity of Anglican orders, issued 18 September, 1896. There are two reasons for the nullity of Anglican Holy Orders. After explaining these two reasons, I'll respond to the objection that Anglicans/Episcopalians have since "revitalized" their Apostolic Succession through the intervention of schismatic bishops of the Old Catholic/Orthodox/Polish National Catholic communities.
There are two reasons for the invalidity of Anglican Orders and Eucharist: First Reason Against Anglican Eucharist: Invalid Form of Priestly Ordination.
And the second reason is: "Invalid Form of Priestly Intent"--read the rest at "Canterbury Tales".