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Old 18-08-2019, 04:58   #16
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Re: Raw water cooling trap

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If you are familiar with a shuttle valve you could use a magnet in the shuttle to trigger a hall effect switch to hold the alarm off when the shuttle was pushed up near the HE switch. Loss of cooling water flow would allow the shuttle to sink away from the switch triggering the alarm.
I wasn't familiar with them, but from your description I can see imagine they'd work and I can think of some ways of easily integrating them into the current cooling setup without adding points of failure.

ANOTHER clever idea, thank you.
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Old 18-08-2019, 05:15   #17
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Re: Raw water cooling trap

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Well.... Bugger! Seriously. That's really clever and just last week I THREW OUT a water level sensor from a LG washing machine from which I'd scavenged the direct drive motor for a generator.



But hey, that really IS clever.
Thanks. This is how I hooked into the water hose. I drilled a smaller hole in the 3/4" hose than the tubing and pushed the nylon tube in. I did it cause it was quick and easy to test. Of course the pump pressure is low, and it has never leaked

And water pump is a dishwasher drain pump, it pumps 5 gallons per minute.
The entire electrical circuit is GFCI-AFCI breaker protected, and I get no nuisance tripping. I have used this pump now for 4 years. This style pump uses very little amps, and it cost me $12 off ebay. I liked it so much I bought another one. I did spray the exposed laminations with clear coat, and used marine grease on the electrical terminals.

I added a 12vdc PC fan to blow air on the pump as it is used now continuous duty, did not know if it mattered. That little fan is powered by a 15vdc walwart in the grey electrical box.

This pump is extremely quiet, you do not hear it running. It also has a check valve designed by oem pump maker in the input. I screwed a gray schedule 80 pvc fitting on the output to allow hooking up my hose. The original diameter is too big for 3/4 hose.

I have pics and even a video of it running pumping water from bucket to bucket submerged.
https://goo.gl/photos/xghMmuFVaGLXUBq86
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Old 18-08-2019, 10:14   #18
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Re: Raw water cooling trap

Flow switches are notorious for failure. Paddle sticks and therefore always shows flow when there may be none. Believe a temp alarm has greater life span and is less fallible.
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Old 18-08-2019, 14:28   #19
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Re: Raw water cooling trap

One thing the aqualarm water flow alarm does that the above switches may not is to sound an alarm when the water flow is reduced not stopped. For example if you have a few impeller blades sheer off and the volume of water is reduced the alarm will sound.

Not sure how your home made device maybe set up just letting you know how mine works

Cheers

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Old 18-08-2019, 19:57   #20
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Re: Raw water cooling trap

I'd be more comfortable with a temperature probe in the exhaust/water mix immediately downstream of the mixing elbow than I would one strapped onto the outside of the hose.

The problem with pressure sensing devices is that the pressure regime within the exhaust is very active. Rather than any steady pressure there are large surges caused by "slugging" in the exhaust gas/water stream and when motoring in a following sea the water level quiet often submerges the exhaust outlet.

Using a differential pressure sensor with the low side connected to the output of the raw water pump and the high side connected into the exhaust manifold just upstream of the mixing elbow, in order to maximize the differential pressure drop without installing any further restriction in the flow, with the voltage output passed to a voltage comparator may be more effective than just a switch.

These are available at RS Components in various pressure ranges.

This arrangement would also allow monitoring of the flow rate if a calibrated meter was included.
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Old 19-08-2019, 04:31   #21
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Re: Raw water cooling trap

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Originally Posted by RaymondR View Post
I'd be more comfortable with a temperature probe in the exhaust/water mix immediately downstream of the mixing elbow than I would one strapped onto the outside of the hose.

The problem with pressure sensing devices is that the pressure regime within the exhaust is very active. Rather than any steady pressure there are large surges caused by "slugging" in the exhaust gas/water stream and when motoring in a following sea the water level quiet often submerges the exhaust outlet.

Using a differential pressure sensor with the low side connected to the output of the raw water pump and the high side connected into the exhaust manifold just upstream of the mixing elbow, in order to maximize the differential pressure drop without installing any further restriction in the flow, with the voltage output passed to a voltage comparator may be more effective than just a switch.

These are available at RS Components in various pressure ranges.

This arrangement would also allow monitoring of the flow rate if a calibrated meter was included.
Don't measure pressure in an exhaust hose, measure it coming from the raw water pump.

I thought of a way to more easily hook my 5/16 or 1/4 tubing to the 1/2 " hose on the gen raw water pump. At the heat exchanger, last year put in a plastic flush drain, has a screw on cap made for a water hose.
I did that to easily drain out water when it freezes.

I can take a short section of garden hose screw onto it, then adapt other end down to a 1/4" fitting to push the 1/4" tubing on that will run to the washing machine pressure switch.

OR better yet, just get a plastic female hose end, and glue in the end of the 1/4" tubing that will run up to the pressure switch. Could even be hot glued, the pressure is very low.

People are getting too technical about this, you want it easy, cheap, robust.
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Old 19-08-2019, 18:18   #22
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Re: Raw water cooling trap

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Don't measure pressure in an exhaust hose, measure it coming from the raw water pump.

People are getting too technical about this, you want it easy, cheap, robust.
The problem is that the pressure is not constant even when the flow rate is, so where do you set the switching pressure.

By using a differential switch or transducer/comparator device you are only measuring the pressure drop across an orifice due to the flow rate, any surging back pressures are "felt" equally by both sides and therefor cancel out.

I like the idea of being able to watch the inferred flow rate on a meter. Since we tend to cruise at about the same throttle settings most of the time it might prove to be a good diagnostic tool.
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Old 30-08-2019, 16:49   #23
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Re: Raw water cooling trap

I use the same style sensor for my coolant temp and my exhaust . I think it activates the alarm at 200* maybe a little more. All I did was add a "t" right at the exhaust elbow and put the temp sensor. It sounds the alarm in about 1 min without water flow. Cheap about $30 for a oil and water sensor with buzzer.

https://www.westmarine.com/buy/sierr...-kit--10533636
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