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Old 20-01-2018, 17:39   #61
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Re: Burned up new raw water impeller

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Originally Posted by kmacdonald View Post
With a worn pump there won't be 3 feet of water in the siphon break, it would have drained out. With 3 feet of water in the uphill and downhill side of the siphon break there will be zero head. They cancel out. If you have a siphon break between the seacock and raw water pump your system is designed wrong.
Since the water lift muffler is way below the siphon break, there normally isn't any water between the siphon break and the muffler (that's the purpose of the break), hence the pump has to get the water to the siphon before it can fill the tube to the exhaust elbow. We're talking about a system that has been shut down, opened, and full of air. If the seacock wasn't closed before opening the pump and the above-waterline-strainer was opened, it is dry also. Hence the pump has to pull the water from the waterline to the strainer, then push it to the siphon break.

I call this priming: Close the seacock, fill the above-waterline-strainer, lube the strainer gasket/o-ring, put the lid on the strainer, open the seacock, and the pump works.
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Old 20-01-2018, 17:50   #62
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Re: Burned up new raw water impeller

IF YOU NEED TO DO ANYTHING TO PRIME THE RAW WATER INTAKE, EXCEPT START THE ENGINE, THERE IS A PROBLEM WITH YOUR COOLING SYSTEM. COMPENSATE FOR THOSE PROBLEMS AT YOUR ENGINES OWN RISK.
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Old 20-01-2018, 17:58   #63
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Re: Burned up new raw water impeller

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Originally Posted by kmacdonald View Post
IF YOU NEED TO DO ANYTHING TO PRIME THE RAW WATER INTAKE, EXCEPT START THE ENGINE, THERE IS A PROBLEM WITH YOUR COOLING SYSTEM. COMPENSATE FOR THOSE PROBLEMS AT YOUR ENGINES OWN RISK.
Thank you for you opinion, not sure why you are yelling.

With 6000 hours cumulative across 3 engines, I take the risk!
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Old 20-01-2018, 18:00   #64
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Re: Burned up new raw water impeller

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Since the water lift muffler is way below the siphon break, there normally isn't any water between the siphon break and the muffler (that's the purpose of the break), hence the pump has to get the water to the siphon before it can fill the tube to the exhaust elbow. We're talking about a system that has been shut down, opened, and full of air. If the seacock wasn't closed before opening the pump and the above-waterline-strainer was opened, it is dry also. Hence the pump has to pull the water from the waterline to the strainer, then push it to the siphon break.

I call this priming: Close the seacock, fill the above-waterline-strainer, lube the strainer gasket/o-ring, put the lid on the strainer, open the seacock, and the pump works.
To "PRIME THE PUMP" the pump needs to suck water from the seacock to the raw water pump. That's it.
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Old 20-01-2018, 18:05   #65
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Re: Burned up new raw water impeller

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Originally Posted by kmacdonald View Post
To "PRIME THE PUMP" the pump needs to suck water from the seacock to the raw water pump. That's it.
Most people protect their raw water system with a strainer in between the seacock and pump. That does figure into the equation along with it's placement.
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Old 20-01-2018, 18:16   #66
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Re: Burned up new raw water impeller

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Most people protect their raw water system with a strainer in between the seacock and pump. That does figure into the equation along with it's placement.
Yes they do and it is a common source of leaks. They need to be resealed from time to time. For safety and convenience they are often placed above the water line. That way they can be cleaned without closing the seacock and serious leaks in it might not sink the boat.
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Old 20-01-2018, 18:51   #67
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Re: Burned up new raw water impeller

Raw water strainer maintenance: Rebuilding A Perko Bronze Sea Strainer Photo Gallery by Compass Marine How To at pbase.com

If you haven't read all of Maine Sails how to's you should. https://marinehowto.com/

He is a true professional and his advice can be counted on as gospel.
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Old 20-01-2018, 19:41   #68
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Re: Burned up new raw water impeller

You must be under sail to roll far enough to expose your keel where your through hull is gulping air !
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Old 20-01-2018, 21:39   #69
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Re: Burned up new raw water impeller

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You must be under sail to roll far enough to expose your keel where your through hull is gulping air !
Not really.... a good swell over tide situation such as you can get in Canal Chacao or Estrecho de la Maire will do it... with no wind at all.

That said when I get back to town in June I am replacing everything between seacock and pump.... including the strainer. That was planned some months ago.....
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Old 21-01-2018, 18:43   #70
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Re: Burned up new raw water impeller

I have the same engines in my cat. The can be finicky about picking up a prime after an impeller change. I grease the impeller, fill the strainer an run the engine at 2000rpms for about 30 seconds. If that doesn't work, I loosen the cover plate till some water leaks out then retighten it and run the engine. I believe that the pump get air bound and loosening the cover lets the air escape and be replaced by raw after. Good luck!
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Old 22-01-2018, 07:21   #71
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Re: Burned up new raw water impeller

I used to squirt some dish soap into the pump to lubricate the impeller. Then check the exhaust for bubbles...
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