Flow Sensor Maintenance

[Peter]

I would suggest that if you found a bigger sensor that was wired correctly, the system would work in the sense that it would still give you a warning when the flow was "low". The definition of low would be a little bit different however.

If you could not find a larger sensor with the appropriate wiring, you could install some circuitry (a relay for example) to reverse the logic.

If you are determined to not lose flow and you cannot find a larger sensor that is wired right, you could install a bypass around the sensor to let the missing 7% through the system.

Both of these latter two ideas would make the whole system a bit more complex and therefore introduce more potential failure points.

You may also be able to restore flow rate by changing fittings and/or hose sizes in your cooling system. I have no doubt that some clever engineer will be able to tell us what changing from a 1/2" to a 5/8" hose would do to flow rate.

You do not mention if you are using a thermostat. if you are, unless the reduction of flow leads to the thermostat not being able to regulate the temperature, i think your engine will run at the same temperature with or without the sensor. The thermostat will adjust to get things to the same temperature.

It is true you will have lost a little "reserve" cooling capacity that you might notice under extreme conditions - running into a stiff headwind in warm seas might get your thermostat to the end of its travel.

As for the MMI pump, there are other advantages to such a pump other than its increased flow rate. Bearings versus bushings so no regular greasing required being the most attractive for me.

I guess at the end of the day it is a case of the design process being a situation that requires balancing one thing against the other. The flow rate sensor, I have the impression, was already in use with the existing Cole-Hersee system and presumably Neil determined that any advantages of going to a different sensor were outweighed by the disadvantages of changing sensors - upgrading to the EWDS would not involve buying a new sensor if you already had the Cole-Hersee system for example.

He clearly considered the flow rate issue and in his estimation it was not of sufficient concern to warrant a change. A different designer might have made a different decision but at the end of the day, it is quite likely that both systems would have ended up with an engine running at the same temperature under normal operating conditions with similar, but not identical, reserve cooling capacity.

Phew, hope that is not too much! More so, hope it is useful.

Peter

[Wrsteinesq]

I love this forum. Thank you all for sharing, generously, your time, your ideas, and your thoughts. What a lot of brain power/wisdom/consideration! I think I’m likely to try to find some workaround so as not to lose that “excess” cooling capacity. To me, anyway, having excess cooling capacity is kinda like having too much money: it’s a condition I can generally recognize in others, but somehow have never managed to diagnose myself with. I absolutely see Peter’s view of how Neil likely came to use the existing sensor, and sure, that makes sense for the fleet writ large; but selfishly I’m still wanting a solution for my situation alone, and that will likely involve a fairly unique solution. I’ll keep y’all posted as to whatever I come up with. With appreciation—

[ndutton]

If the real goal is maximizing your cooling capacity and once again looking at the total system, increasing the size of your HX to the largest 4 pass HX you can physically fit makes more of a difference than any other system modification. Other things you can do to achieve the goal are upsize your hoses, upsize your raw water intake thru-hull, upsize your raw water strainer, reduce system elbows to an absolute minimum, get rid of the thermostat and completely close the bypass.

And yes, either upsize or eliminate the flow sensor.

[Wrsteinesq]

Respectfully, I think you may be misunderstanding my objectives. I never said that my real goal was to maximize my cooling capacity, although if that were my goal, you have graciously suggested a number of ways that could be accomplished, some more involved than others. I made it quite clear that I do not believe that I have an overheating problem.

But not wanting to sacrifice ‘excess’ cooling capacity which I already have, is a very different thing from seeking to increase that cooling capacity.

Everyone seems to agree that the standard flow sensor does in fact involve some degree of flow impediment. I now have a better understanding of how I might re-order various components, like putting the PSS tee downstream of the sensor, which may help even out distribution, but which doesn’t address the actual flow reduction. But it still seems to me that the degree of that sensor-induced flow impediment is greater with a higher flow raw water pump like the MMI one: if you tried to flow a garden hose flow thru a mousehole it would be less impeded proportionally, than if you tried to flow a river thru it. I wasn’t asking about how to make a bigger river, but rather how to better utilize the river I already have.

Which is why my question went to, is there a bigger mousehole available?

Again, thanks to all.

[ndutton]

Everyone seems to agree that the standard flow sensor does in fact involve some degree of flow impediment.

That was never in dispute. Even the product description in the MMI catalog says it does. Another way to look at the 7% restriction is the MMI sensor maintains 93% flow.

edit: there are ultrasonic clamp-on flow sensors (external mount only) available that do not impart any restriction. The one I saw has a pulse output that would have to be translated to be useful for our EWDS.

[sastanley]

I see two more tests that could be done to figure this out.
Put a valve on the PSS to eliminate it from the equation for testing. (may need to provide alternate cooling source temporarily unless testing at the dock out of gear.)
Test/observe flow rate with and without the flow sensor to determine if it is a problem.
If I had a choice between a spring in my way or an open path, I'd take the open path every time. This same problem was solved with a ball valve in the sideplate bypass years ago.
My $0.02.

[Antibes]

The PSS does not need cooling water fed through the hose in a sailboat application