No, you should check out the book so they know people are interested in it and perhaps then will order more copies. Maybe it would then be ok to download it and use it for the period you have it checked out, but even that is debatable because then you might be supporting the continuation of the illegal distribution, causing more people to download it illegally.
And a single copy can only service a small number too, not an infinite number, as only one person can be in possession of it at one time and usually borrow it for weeks at a time.