pressure washer still doesn’t pass water after inspecting check valves. What next?

Check valves look fine. It's industrial pressure washer. 7.5hp, 240v, 3phase motor diesel burner. Previous owner reports ud 10 years, functioned fine then. ideas?
I 3 phase power, electric motor runs fine.
The motor spins, pressure doesn't rise. tried 6 days ago. 5 10 seconds, ruin pump. Today, pump check valves dry, visible internal pumps cd see.

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50ft New 6000 PSI Blue Non Marking Pressure Washer Hose
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Is a Generac 2250 psi Pressure Washer Good?

I thinking buy ud Generac 2250psi Pressure washer. te pressure washers? 6hp briggs straton engine. Im paying 0 Canadian. curious quality cheap pressure washers.

BRAND NEW High Pressure Water Gun Cleaner Air Tools
BRAND NEW High Pressure Water Gun Cleaner Air Tools
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50ft New 6000 PSI Blue Non Marking Pressure Washer Hose
50ft New 6000 PSI Blue Non Marking Pressure Washer Hose
Paypal   US $65.00

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