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Old 30-07-2015, 17:58   #1
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Raw Water flow sensor switch alarm

I am thinking about putting a flow sensor/switch/alarm inline between the raw water intake pump and the heat exchanger. Has anyone done this? Any luck. I believe it will help me recognize an overheat before it happens.

any thoughts?

thanks
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Old 30-07-2015, 18:09   #2
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Re: Raw Water flow sensor switch alarm

Nothing wrong with your idea.

Another possibility is fitting a exhaust pipe temperature gauge (or alarm). This can be as simple as a thermocouple style sensor clamped to the exhaust pipe very near the water injection point.

First indication of reduce raw water flow is a rapidly rising exhaust temperature. Only works with wet exhaust of course.
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Old 30-07-2015, 18:23   #3
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Re: Raw Water flow sensor switch alarm

I will be interested in this thread also as I now own a boat that the exhaust is out of sight very near the waterline all other boats that I have owned you could see the water or hear the tone change
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Old 30-07-2015, 18:35   #4
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Re: Raw Water flow sensor switch alarm

The next concern is which type of flow sensor. Obviously it has to withstand salt water, So that eliminates some of them. Some types are plastic/PVC but have metal springs. Some are stainless...some have no moving parts, but those are expensive.
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Old 30-07-2015, 18:40   #5
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Re: Raw Water flow sensor switch alarm

I would like to ask if I could see someone's pee hole set up but did not know how to ask without seeing some weird stuff
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Old 30-07-2015, 18:53   #6
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Re: Raw Water flow sensor switch alarm

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Originally Posted by sartorst View Post
I would like to ask if I could see someone's pee hole set up but did not know how to ask without seeing some weird stuff
I'm right in the middle of making one now. Will post picture when finished!
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Old 30-07-2015, 18:57   #7
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Re: Raw Water flow sensor switch alarm

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Originally Posted by kevins View Post
The next concern is which type of flow sensor. Obviously it has to withstand salt water, So that eliminates some of them. Some types are plastic/PVC but have metal springs. Some are stainless...some have no moving parts, but those are expensive.
Another reason why I'm going to a exhaust pipe temp indicator (not exhaust gas). A flow sensor also adds a piont of failure in the raw water circuit. Plenty of off the shelf units and easy to fit.

Still, its not a bad idea!
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Old 30-07-2015, 19:03   #8
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Re: Raw Water flow sensor switch alarm

Yes, most of them seem like they will break before the impeller. The temperature sensor, I suppose you can get one that goes off at a certain temperature, that would work well.
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Old 30-07-2015, 19:19   #9
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Re: Raw Water flow sensor switch alarm

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Yes, most of them seem like they will break before the impeller. The temperature sensor, I suppose you can get one that goes off at a certain temperature, that would work well.
Aqualarm make several varieties of flow and temperature alarm devices. They are well regarded by many users and sell through many chandlers and online sellers such as Defender.

https://www.aqualarm.net/
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Old 30-07-2015, 19:20   #10
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Re: Raw Water flow sensor switch alarm

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Yes, most of them seem like they will break before the impeller. The temperature sensor, I suppose you can get one that goes off at a certain temperature, that would work well.
The alarm mode on the Engine Watchdog TM2 or TM4 seems to be user set. Another CF menber Snowpetrel put me onto this particular item but I reckon there would a lot of them made in other parts of the world.
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Old 30-07-2015, 20:25   #11
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Re: Raw Water flow sensor switch alarm

I wouldn't bother with a flow valve as it would be just one more thing to fail. I purchased an normally open thermal sensor for a couple of dollars from the local electronics store. They use them mostly for amplifier output stages (I think) and are available in different temperature ratings. Clamped it to the stainless water lock (on my last boat I clamped to the exhaust elbow) and wired it to the bilge high water alarm. Cheap and works.

I'm also going to add a "pisser" soon since at the moment I have to poke my head over the side of the boat every time I start the engine and that won't tell me if flow stops while in operation. This gadget ejects a trickle of water from the raw water into the cockpit so water flow is always observable. I did make up the plumbing to fit, but realised it's easy enough to modify the vented loop to do the job.
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Old 31-07-2015, 09:26   #12
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Re: Raw Water flow sensor switch alarm

There is a new breed of flow sensors coming on line that use ultrasonic technology, that has no moving parts it is complicated and will be expensive now, but over time they will become commodity products. Very accurate they are used in medical devices.
For now, if you have room for it a standard old mechanical flowmeter would be fine. They type that is a floating ball in a clear tube. They have been around since the age of steam engines and still are being used where fluids flow in pipes!
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Old 31-07-2015, 09:37   #13
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Re: Raw Water flow sensor switch alarm

On two of the 12V watermaker/gen sets I built I just put a "snap disc" thermostat on the water cooled wet exhaust, as mentioned above by Wotname. They are available from Grainger and are cheap. They can turn a light or a buzzer on when activated.
It's just a little disc shaped item that you buy to close at a given temp.
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Old 31-07-2015, 09:48   #14
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Re: Raw Water flow sensor switch alarm

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I'm right in the middle of making one now. Will post picture when finished!
Oh, Dear! Do be careful you don't frighten the horses ;-0)!!

TrentePieds
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Old 31-07-2015, 10:13   #15
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Re: Raw Water flow sensor switch alarm

snap disc pic:
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