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Old 18-06-2021, 18:38   #1
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No raw water flow when strainer is in circuit

I have a 1983 Volvo MD11D with a OEM heat exchanger. It is currently on the hard, getting ready to launch. When I run the engine the conventional way (raw water strainer intake hose in a bucket of water), I get little to no water flow out of the exhaust. But when I bypass the strainer (raw water pump intake hose in the bucket), I get plenty of flow. Impeller and gasket are new, I tightened the "sealing" bolts on the strainer, primed the system by filling the strainer with water, put a dab of silicone grease around strainer gasket, still no flow. At the end of last year's season, flow when the boat was in water was fine. Someone suggested I rebuild the water pump, but before I open that can of worms, I wanted to check if there was a really basic "physics" reason for the strainer-dependent flow and if I can hope/expect good flow once I'm back in the water, with ocean hydrodynamics in play.
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Old 20-06-2021, 10:26   #2
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Re: No raw water flow when strainer is in circuit

Vane pumps have somewhat limited ability to self-prime, because they are not very good air pumps. They are better at moving bunches of water with some positive pressure continuous on the "suction" side. My guess is that the various sources of problems for the pump, including narrow hose, strainer, and lift got beyond your pump's ability to prime.
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Old 21-06-2021, 17:33   #3
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Re: No raw water flow when strainer is in circuit

Obviously nothing wrong with the pump.......works fine when direct connected!

Most likely an air leak into the strainer is causing decreased water flow. Can be checked by installing a clear suction line between the strainer and the pump and look for air bubbles when running.
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Old 22-06-2021, 04:22   #4
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Re: No raw water flow when strainer is in circuit

Great point, Doug. I didn't even think of that. An air leak there would reduce the ability of the pump to prime.
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