You need an isolation valve between the pump and the system it feeds, and a tee between them with a valve on the side outlet.
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The idea here is that a pump that is otherwise okay will have trouble priming without something to "push against" ~ and a sprinkler system often cannot meet this requirement. That's where the isolation valve comes in. Close that valve. Slightly open the side-outlet valve on the tee between the pump and the isolation valve. Prime the pump. If it is in good working order, you will achieve a full flow from the side outlet, opening it wider, as needed. Then you can simultaneously close the side outlet, while opening the isolation valve, in effect transferring the flow to the system.