Sump pump cycling

I've recently installed a sump pump in my basement, During a continuous downpour I noticed that the pump came on every 30 seconds. That is about 15 sec of pumping followed by 15 sec of refill of the sump. This seems to be too often.
One thing I noticed is that when the pump stops pumping a large amount of water returns to the sump which means the back flow valve probably isn't functioning as it should. Are there any other things I should be looking at?
What is an acceptable pump cycling time?
Thanks!

That valve must be close to the pump and in good order. I think Ira Woods sells the zoeller for an amazing 16$. Other than that you are SOL without a drought.