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Discussion Starter · #1 ·
Not woodworking, but you guys always come up with ideas for me.

I have a new (to me) sailboat that has a small inboard engine. The engine sucks in cooling water through a hose from a thru-hull fitting that’s below the boat’s waterline.

The boat is kept on a boat lift which raises it out of the water when not in use. When it’s raised, all the water runs out of the hose that supplies the cooling water and the pump loses its prime. As a result, when re-started, there’s an air lock and the pump sucks air for quite a while before establishing enough suction to pump water.

I’m planning to put a tee in the intake line and lead a hose to a valve where I can vent the air, causing the water to rise up the hose.

Wheh! That was a lot of background to get from my question.

I’m looking for a valve that I can use to release the air then close afterward. Since like other old people, I have CRS, so I’d like for the valve to return itself to the closed position so I don’t have to worry about forgetting to close it.

Any suggestions for a “dead man” valve?
 

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I’m planning to put a tee in the intake line and lead a hose to a valve where I can vent the air, causing the water to rise up the hose.
How about a self closing check valve so the water will not drain out in the first place? If the water is prevented from draining, the pump will remain primed at all times.
 

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Discussion Starter · #3 ·
How about a self closing check valve so the water will not drain out in the first place? If the water is prevented from draining, the pump will remain primed at all times.
Hmmm… Interesting idea.

I think I’d have to put the check valve as close to the bottom of the hose as possible and access there is “challenging”. Also, it would need to be drained in the winter. But, certainly food for thought.
 

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I personally would never screw with intake pumps and bilge pumps normal operation. I have once with my bilge pump on my sailboat and almost sank it. I don't know why your pump is taking so long to pump though. The only time my boats were ever out of the water were for their once a year hull and thru-hull inspections and anti-fowling painting when necessary. When dropped back in the water usually a week or two later, the cooling water came out relatively quickly.
CruisersForum.com would be a very good place to ask this question.
 

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Smart and Cool
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What is the condition of the impeller?

Several sources point to the impeller for similar issues.

Most trailered boats go through the same thing, pulled out of the water, put back in the water, no issues with water unless the impeller is not in good condition.

I would start there instead of trying to build a solution to hide the real issue.
 

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Smart and Cool
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I just replaced the impeller. The impeller it replaced was in perfect condition as well.
I would check all of the hoses as well.

See if you can create a high loop on the intake to the impeller so it doesn't drain out all of the way. The block shouldn't be draining out as well.

Does the motor overheat when it is "airlocked"?
 

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Termite
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I would check all of the hoses as well.

See if you can create a high loop on the intake to the impeller so it doesn't drain out all of the way. The block shouldn't be draining out as well.

Does the motor overheat when it is "airlocked"?
I would check the hoses as well.
 

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Discussion Starter · #10 ·
I would check all of the hoses as well.

See if you can create a high loop on the intake to the impeller so it doesn't drain out all of the way. The block shouldn't be draining out as well.

Does the motor overheat when it is "airlocked"?
the motor doesn’t overheat, but having the impeller running dry doesn’t seem ideal. It does eventually prime at higher rpms, but a dry impeller at high rpms sounds even worse.
 

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Discussion Starter · #11 ·
By the way, the guys on the boating forums say that if it eventually primes no worries, but a dry running impeller doesn’t sit well with me. I think venting the air will work, I just need a foolproof valve.
 

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If the boating forum is aware of this and say okay, then I don't understand?.
 

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If the boating forum is aware of this and say okay, then I don't understand?.
Because some folks just don't get it. Dry rubber impeller rubbing inside a dry housing is not okay. The heat from the friction can and will do damage and premature wear.
No different than the difference in grinding a chisel "dry" and allowing the heat to build up, or grinding it wet to lubricate and remove the heat.
 

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Because some folks just don't get it. Dry rubber impeller rubbing inside a dry housing is not okay. The heat from the friction can and will do damage and premature wear.
No different than the difference in grinding a chisel "dry" and allowing the heat to build up, or grinding it wet to lubricate and remove the heat.
Are the boat techs talking to him or just forum runners?

If it's coming out of my pocket, I'd want to talk to the correct people...
 

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The folks that aren't getting it, are the ones that are trying to put a bandaid on the "problem". Impeller pumps are self priming, adding check valves or air vents is unnecessary if the system is functioning correctly. Millions of inboard motors on boats going in and out of the water have the same set up without adding check valves or air vents.

The way the raw water impeller works is to create a vacuum in the tubing, valves and transmission cooler (on V-drives) in order to draw in the water from the water inlet on the bottom of the boat and then pump the water and prime the centrifugal water pump on the front of the motor. In order for it to be able to draw in the water, the amount of vacuum it's able to create is critical as it effects how long it will take to draw in the water (which also cools and lubricates the pump impeller). The amount of vacuum that’s created is affected by any loose clamps, fittings, impeller condition, pump housing condition, collapsed intake hose and rear seal condition. One simple method to check for leaks is to disconnect the raw water intake and attach a garden hose. Turn the hose on with the motor off and check for any leaks (look for small drips). Next, start the motor and check for leaks (drips) at the back of the raw water pump and the pump cover. Once all the leaks have been eliminated and if the problems persist look for issues with the pump itself. Any score marks or scratches to the inside of the housing (including the front plate and back housing) from overheating or from sucking up debris will greatly effect its performance. One small but important feature to the raw water impeller are two small groves on each side of the impeller hub just above the brass center. These small groves allow a small amount of water to flow into the front and back of the housing to seal and cool these areas of the impeller, housing and rear seal. They’ll be easy to see on a new impeller, but a used impeller may have them filled with debris, grease or worn to a point where their no longer there and could have caused damage to the housing. If you still have problems, trace down the hose from the raw water pump to the intake. Since its cold water only there shouldn’t be any other rubber lines running off of it, but you never know… One last thing (shown below) is what Johnson Impellers suggests on impeller issues.

Reduced flow will occur when the impeller is damaged. However, bowed, missing, work or ripped blades will cause reduced flow. A worn cam, wear plate, or cover plate will also reduce flow. The replacement of these parts when worn actually cures the problem. Another cause of low flow is an air leak. This can occur anywhere along the suction line, within the sea strainer, or within the pump. Check all hoses, pump gaskets, hose clamps, fillings and the pump water seal. Regularly clean your suction strainer and confirm all old impeller blades are removed when replacing your impeller.

How to prevent pump failure: The main causes of premature impeller failure involve running the pump dry, with a restricted suction or with a blocked discharge. Confirm your inlet seacock is in the open position before engine start. You would be surprised how often this simple step is forgotten. Regularly clean your suction strainer and confirm all old blades are removed when replacing your impeller. These steps will reduce the majority of system flow restrictions.


It is also possible to install the impeller incorrectly, you should always check that it was installed correctly.
 
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