depends on the installation, if I can get by without one, I will. It really hurts the flow of a pump. But I've had installations where there was enough water in the hose, that when the auto switch shut off, the water would back flow and cause the auto switch to come on again, fill the hose, shut off, back flow, repeat over and over till the pump was burnt out. You can play around with loops in the line, raising the float switch height, and lowering the pump to prevent this from happening, but sometimes, theres no other solution than a check valve. BTW, make sure to use smooth hose for your pump installation, the corrugated hose really cuts down on the flow
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