Raw water flow alarms

[Ruffles]

The overheat alarm came on today. Inlet blocked with weed. I had to replace the impeller as well - possibly because of the impeller running dry.

Anyway, SWMBO says I can purchase a flow alarm. I've found this one which seems reasonable. There's also one from Halyard but I can't find a price on-line. I suspect that means it's expensive.

Any recommendations?

 

[mainmarine]

you can get a simple flow switch from Radiospares for around £15, you will also need a relay to change the output for £5 a bit of wire and a buzzer or light. I have made several of these, fitted in the sea water inlet pipe they give an early warning that water is not flowing, before the engine has chance to overheat.

 

[ebbtide]

Delighted with the Halyard sensors, one in water flow, another exhaust temperature. Can't start the engine without a screech reminding me to open the iseacock!

 

[dukes4monny]

I would be interested in doing this for my Yanmar 2GM20. Which sensor from RS would you suggest using?

Thanks for your help.

 

[srp]

If you can wield a soldering iron you can make one yourself - details here. The flow switch comes from CPC and there's a catalogue reference number on the linked page. For an engine bigger than a 1gm10 with a bigger flow rate you might want to use a larger size. From memory I think CPC do two sizes.

 

[nimbusgb]

[ QUOTE ]
I would be interested in doing this for my Yanmar 2GM20. Which sensor from RS would you suggest using?

Thanks for your help.

[/ QUOTE ]

Check your inlet hose first. the sensors come in 15mm and 22mm fittings. You'll probably need the 22mm.

If you need the 15mm I have a couple lying around.

I bought a couple of ABS reducing bushes and cut them back to fit into my intake pipe since mine is 32mm.

web page

Mount the unit as close to the pump as possible, and certainly above the normal water line of the boat so if anything goes wrong its not a potential boat sinking leak. Also if your boat is MCA coded you may have to protect the unit from heat / fire.

The flow switch energises a relay to reverse the polarity ( N/O to N/C ) so when flow established, relay energised, output contact opens. Buzzer and light driven by the relay contacts go out / off.

In the diagram above you could have either warning circuit ( or both ) if you dont have a buzzer / alarm then you can wire in a new one. If you do then just add the bit into the existing oil pressure circuit.

Relays are bit more robust than LED's and transistors in the engine room and also the way this is wired if the flow sensor fails the circuit is somewhat failsafe.

 

[Ruffles]

Many thanks for the responses.

I'm concerned that the RS sensor isn't adjustable. Does this matter in practice? I generally find there's always some weed in the filter and presumably even when critically constricted there will be some water flow which might prevent the alarm from sounding.

The fifty quid unit in my post states that it can be adjusted. And seems good value.

 

[brians]

Did this happen with a saildrive and how did uou clear it?

 

[Ruffles]

[ QUOTE ]
Did this happen with a saildrive and how did uou clear it?

[/ QUOTE ]
No, sorry. Bog standard bronze water inlet. It's shaft drive.
I believe others have bypassed the saildrive inlet to a standard skin fitting for the very problem you're experiencing. Might be worth a google. I guess this removes the cooling to the saildrive. Bit it's immersed aluminium so surely it can't get that hot?

 

[maxi77]

On the other hand I never had any problems with the sail drive, perhaps the position of the inlet away from the hull has some effect, but I do have to clear the conventional strainer in my present boat.