We are trying to pass a hidden value to the Priority field with our web to case form. We are using this syntax, but it's blank in the created case: 

<input type=hidden name="Priority" id="Priority" value="Level 3 - Medium">

Is there something wrong with this syntax? Is it just not possible to set a value to this field? Other hidden fields are working in our form. We also tried leaving it off the form entirely and using the picklist's default value to set the value, but this still left us with a blank field.