back pressure valve

I have a water ace deep well jet pump that is 35 yeas old. the only thing that I have done to that pump over the years is to replace the switch several times and bend new hooks on the starting capacitor governor springs. Recently the switch malfunctioned again so I decided to replace the pump only because it's a 60 mile round trip to work on it. I replace it with a Water Ace since the old one gave me such great service. I couldn't get the old back pressure regulator out of the old pump so as a matter of convenience I simply installed a tee instead and it works fine. Can someone that has experienced the ramifications of not using a back pressure valve tell me what problems might occur from the absence of the valve.