My water pump impeller has been lossing blades. When I took off the hoses to the vacuum break valve to find the pieces, I found that the vacuum break valve has a multi stepped nipple that is only openned for the smallest openning. I would like to know if I should open up to the largest hole possible? This would allow more water flow but if a blade breaks off the impeller it would make it to the heat exchanger. I have never had a problem with over heating so enough water has been getting through.