So why should you always keep at least two valves open? For starters, the position of the valve determines the flow and direction of the water.

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Most pools will have at least 2 suction side valves and 2 return side valves. Of course, this varies between pools, but here, we're talking averages. There will be one valve for the skimmer and one pool valve for the bottom drain. On the return side, we can find valves controlling the returns and maybe a water feature or two.

Maintaining two open valves will not only allow for the best water flow and circulation, it's a great safety feature. If one suction side gets clogged or the water flow is somehow restricted, your pump motor will still draw water from the other side. By always having two valves open, the chances of having both suction side lines clogged or restricted is diminished.