how to disabble required attributes MVC model?

i have a model :

  [Range(1, 24, ErrorMessage = "Invalid Hour")]
    public int val1{ get; set; }
    [Required(AllowEmptyStrings = true)]
    public string val2 { get; set; }

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i have a edit action also i have view page. There are 2 textboxes val1.text, val2.text if i write fill view form (i am not writing any value on val1) return InvalidHour. i want to give ability to set empty value (not writing something on val1). How to do it?