Laravel 5.1 validation - validation

Question

when I use validation in my controller or in a separate request file to validate request of form , it just redirect to itself. But when i remove the validation form just normally update the information please help me.
Here is the route:
Route::group(['prefix' => '{university}'], function() {
Route::Resource('instructor', 'university\univInstructorController');
});
Controller:
<?php
namespace App\Http\Controllers\university;
use App\Http\Requests\university\instructor\instructorUpProfileReq;
use App\Http\Controllers\Controller;
use Illuminate\Http\Request;
use App\instructor;
use App\university;
use Illuminate\Support\Facades\Redirect;
class univInstructorController extends Controller
{
public function update($university,$id, Request $request)
{
if($universities=university::whereuniversityName($university)->first()){
if($instructors = instructor::find($id)){
$this->validate($request, [
'name' => 'required|alpha|min:3',
'lName' => 'required|alpha|min:3',
'gender' => 'required|alpha',
'birth_date' => 'date',
'degree_type' => 'required|alpha',
'academic_degree' => 'required|alpha',
'phone' => 'max:15',
'address' => 'alpha_dash|min:4',
]);
$input = $request->all();
$instructors->update($input);
return Redirect::action('university\univInstructorController#show',['universities'=>$university,'id'=>$id]);
}
else{
return view('errors.404');
}
}
else{
return view('errors.404');
}
}
}