Effect of restricting a pump on the supply side?

[Rangeball]

Assuming one has a valve ahead of the pump, what is the affect of restricting the flow? Reduced flow rate? Lower filter pressure?

My dad has a 1hp AG hayward pump with a smaller DE filter. Flow is unreal, and I think he's probably exceeding are at the very least at the upper end of his filter flow rate. Would closing the pump supply valve a bit help at all?

 

[JasonLion]

Yes. Adding flow restrictions on the suction side increases the suction pressure, which lowers the filter pressure, which will lower the flow rate (give or take some very rare special cases).

 

[mas985]

It usually better for the pump to restrict the return side rather than the suction side. Pumps like less head on the suction side than the return side. When you restrict the suction side of the pump, the pump noise will increase and so will the suction which can cause air to be sucked into the pump basket.

However, when you restrict the return side, flow rate will also decrease but the pump will run quiter and virtually no chance of air in the pump basket. The pressure in the filter will rise some but this is usually not a problem.