raw water alarm options

[eddie]

whats the best sensor?

water loss at mixer or paddle type?

are there advantages one over the other?

Topic

[Dan]

I have outboard water pressure sensors that network through NMEA to my Simrad MFD’s,water pressures are displayed on screen continuously.

They have adjustable alarm settings that generate an audible alarm and a flashing popup warning on screen when pressures drop below the setpoint, connected directly to the output side of the water pump.
Pressures on screen in the pic shown as 71.00 and 72.10 KPA.

https://www.lowrance.com/lowrance/type/sensors-networking/pressure-sensor-pk/

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Kevin Lee

[Edwin Harvie]

Here is my setup, installed on a Sherwood GC5 pump. It uses the existing pressure-side tap, which the Sherwood drawing calls a drain plug but which the Cummins manual indicates as the test point for raw water pressure (book is 15 psi max; no minimum specified). Donald is probably right that a true flow sensor at the farthest downstream point is better, but this seemed easier and cheaper than a flow measurement device. I think I got the kit for less than $100 including tube and fitting. The lowest scale I could find was 30 psi, which seemed like it would do.

I abandoned the Vetus alarm display, which was dim and weak, and drilled a hole in the pressure gauge trim ring for a tiny 12V LED (still too dim) and connected a 12V siren from eBay, which even behind the dash console was so deathly loud that I wrapped it in foam. It gets your attention. I had installed the Vetus sensor years ago farther down the exhaust hose than I recalled (~3 ft?), but you don’t want it any closer to the elbow since during the Chesapeake dog days the water temperature can be 90F, when the alarm will still trigger after coming off plane and idling in for awhile.

I haven’t thought much about how to monitor the water pressure until now. I figured I’d get a baseline with a new impeller and fairly clean raw water circuit and be able to tell by a pressure drop if I sucked up a plastic bag or weed in the strainer, or the impeller starting going bad. I guess it would also indicate a restriction or gradual occlusion upstream in the raw water circuit by a pressure increase. Anyway it seemed like an additional layer of prevention. Don’t ask me how I know how important raw water flow is LOL!

1 user thanked author for this post.

Kevin Lee

[donald roth]

The raw water flow sensor is more effectively located Between the heat exchanger outlet and the elbow or mixer.
At the tail end of the system , it can sense more than just intake blockage or impeller failure, it monitors the rest of the systems parts too, hoses, clamps and coolers that can also fail.
Another bad thing about locating the sensor Immediately downstream of the pump is that it is located in a busy spot in back of the raw water pump, and can be easily broken off when wrestling with an impeller change. (Don’t ask me how I know!)

[Rob Schepis]

Edwin, how about some pics of your setup (engine room and dash), sounds interesting. Thanks for contributing.

[Edwin Harvie]

Like firehoser, I have 2 raw water indicators: a Vetus exhaust alarm temperature sensor just downstream of the mixing elbow and an outboard-type water pressure gauge feeding from the raw water pump 1/4″ NPT pressure tap. The temperature sender gives a “light and buzzer” alarm and the water pressure gauge lets me monitor the impeller and general raw water system health for peace of mind.

I actually installed an LED and loud-as-hell 12V oscillator siren for the temp sensor within the raw water gauge, so all fits into a single 2″ hole in the dash cluster.

[firehoser75]

I have both the Borel exhaust hose overtemp alarm (installed right after the exhaust elbow on the exhaust hose) and a “paddle type” of Aqualarm flow alarm installed in the raw water inlet hose between the sea strainer and the engine mounted SMX raw water pump.
To my thinking, this gives me the best of both worlds. The flow alarm will alert me to several things regarding adequate cooling water flow. If I forget to open the thru hull or the intake becomes blocked by any kind of desbris, or even if the flow drops too low, it will instantly alarm. However, if I had blown a hose downstream of the pump, it would not warn me of that, and I could unknowingly just pump water into my ER, and my engine would probably overheat before the “regular” high temp alarm would sound.
The exhaust overtemp warns of a pending overheat. This is usually the first place that high temps will be noticed, giving an early warning of higher than expected temperatures. The blown hose would show up at this alarm. The exhaust alarm potentially saved me thousands of dollars, as it warned me about a leaking exhaust elbow that due to this leak, was not adequately cooling the exhaust hose. At the time I had one of the “doomed to fail” elbows, and if left (due to just not knowing), it could have sent raw water into my turbo or worse, my engine. All other temp indications were normal, just the hose was hot.
Therefore, in my opinion, they each have their purpose, and I recommend both. They are not expensive, nor very difficult to install, and offer good “insurance” against what could be a costly problem.

[Author]

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