Rails Validation on update

Hello friends,
I am using
“validates_presence_of :password, :if =>
:password_required?”
for password validation but at the time of updating a profile i don’t
want
to use the default validation. So for the same i am calling
validates_presence_of :password, :if =>
:password_required?, :on => :create"

But still the validation is taking place at the time of updating
records.

Any good solutions?

regards
Abhishek shukla