impellor failure monitor

[stefan_r]

I have a nipple just after my impellor on my MAN engines, I spoke to a dealer who says that the raw water circuit runs at around 2 bar (fairly sure it was 2 bar - am checking but the idea is still the same!!!) so if I get a pressure guage, attach it to this nipple and keep and eye on the pressure whilst underway - if it drops from the 'standard' 2 bar then I know I have no water (because no pressure) in the circuit and therefore a plastic bag over the raw water in / shredded impellor???

Can anyone see a problem with this proposed installation??

Cheers
Stefan

<hr width=100% size=1>mailto: stefan@athito.com

 

[Talbot]

strongly resisting temptation to comment about nipples, but resisting it!!!!!


seems like a reasonable idea - alternative method is a temp sensor in the waterways.

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[vyv_cox]

"keeping an eye on" instrumentation is not particularly good practice, as inevitably you will not be looking when something fails. Much better to attach an audible alarm to indicate high temperature, no flow or even no pressure via your nipple, which should be perfectly feasible using an oil pressure switch.

Reserve your gauge for occasional condition monitoring, where it sounds like it could be useful.

I'm a little surprised at 2 bar because there is nothing to provide back-pressure. The pump is effectively acting on an open circuit, via the exhaust pipe. You need to confirm this before specifying your pressure switch.

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[steve28]

a much more reliable way is to use a flow sensor, like the ones used in machines.
the signal from which can be used on a gauge or alarm as well.


steve

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[david_bagshaw]

Impellors dont always totally fail, surely it would be better to monitor the wet exhaust temp, as exhaust pipe overtemp produces the biggest risk.

<hr width=100% size=1>David
<A target="_blank" HREF=http://www.euroboating.net>http://www.euroboating.net</A>

 

[wpsalm]

reckon in most cases temp alarms don,t go off until damage is done....as for the cooling water intake plugged by plastic bag this does,nt happen as long as the vessel is underway...no doubt someone somewhere has caught a plastic bag or jelly fish while underway but the chances must very remote...so the time to be alert is whenever the engine is running while out of gear. charging batteries at the dock etc. which is not a good practice but sometimes nessesary so keep an eye on your exhaust. on my boat have a small deisel driven alternator for battery charging at anchor...and I protect it with a flow alarm that was designed for bait tanks on sport fishing boats ... the alarm is available through west marine...

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[Guest]

Why not just a simple manometer or red ball in pipe indicator ? ...... if theres flow the ball jiggles around at the top of pipe etc.


<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[david_bagshaw]

Well strangely have had underway total blockages caused by:-


1 Large eel on the islemeer, which was unbelieveably difficult to remove, blood & guts everywhere

2 jelley fish in the baltic, back flush them though

3 plastic bags by the doz in the belgian canals beds on the props , but that is another story

4 lemna ditto & french

5 solid oil /tar Charleroi B


none of which were protected by alarms, none of which damaged the exhaust system, all detected by keeping an eye on the engine panel

<hr width=100% size=1>David
<A target="_blank" HREF=http://www.euroboating.net>http://www.euroboating.net</A>

 

[onenyala]

I have done away with the syphon break valve and taken a small plastic tube from the spigot into the cockpit. When the engine runs some water is diverted through the small bore tube and into the cockpit as a telltale. If the impeller fails the water stops and steam comes from the tell tale. It becomes second nature to glance frequently at the tell tale. It averted a disaster coming out of Weymouth a couple of years ago.

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