Sump Pumps

I get water under my basement floor periodically. I installed five 1/2 hp pumps each with a 1.5 inch diameter pipe. The five outgoing pipes are tied into a 4 inch pipe. I am looking for a 4 inch check valve to prevent any back flow. Does anybody have any ideas where I could find such a check valve? I have to replace a couple of the pumps because they were running dry. Can anybody suggest a good sump pump. The water has to travel up about 6 feet and then horizontal for about 35 feet.

Thanks for your help

The pumps should each have their own check valve.