So why does my Generator impeller last forever.

[Fuss]

It never wears out, it used to last 20 seconds if it did not get water, thats right , 20 seconds, whether brand new or used, it made no difference, no water then 20 seconds.


I think yours is the same, unless you installed one of those fancy magnet pumps for a few hundred.


Anyway, for me 20 seconds was too short and I decided to fix it. Would you like to have 45 seconds or maybe even 3 minutes , I bet you would, but even if I gave you 3 minutes it would not help, we would just be transferring the problem from your little impeller to some more expensive part of your generator.


I know, I know..... no I did not read about renewables and solar panels and how you can then remove your generator. I know you want me to but I'm not going to.


Ok, so where was I, ah yes , your demanding, sensitive little impeller thats calling all the shots, perhaps it should be made captain, demanding, clear consequences, clear easy to understand rules, no water, then no impeller. All traits that help make a good captain, lets then not talk about you, lets stay on the impellor subject shall we.


So, what to do....Well I figured out that my generator was switching off instantly when it had no oil pressure, this is a good thing. I also figured out that when the generator overheated, it also switched off, sort of a good thing but it switched off around 3 minutes after it got no cooling water... this is sort of a good thing but also a bad thing. Lets not dwell on this minor point.


Ok, so what did I do.
Remember what I said about the oil pressure and instantly switching off...well I got a pressure switch that is adjustable between 1 bar and 10. I measured the number of bars pressure in the sea water cooling line ...after the pump, after the pump of course and I then set the pressure switch to switch on 1 bar less than the normal pressure. I then installed this and wired it in parallel, in parallel with the oil pressure switch off safety circuit.
Thus my impeller gets no chance to complain or take any action as I and the pressure switch are always 1 Step ahead.
So much so that if I switched off the sea water cooling supply (sea cock, this is called) then the generator instantly, instantly stops, sort of like magic really. Its been functioning perfectly for years and so I never have to replace the impeller.... you know what I mean, not actually never, but nearly never.

[rslifkin]

That's a good idea. My generator has a high exhaust temp shutdown as the first line of defense for lost cooling water. Not quite as instant as the water pressure shutdown, but it'll trip for exhaust temp long before the coolant temp gets high enough for a shutdown.

[team karst]

I put low pressure (~5psi) gauges in RW system as a trial. Even with Wika SS wetted parts, life was a problem. Probably foreign material blocking. Hopefully, switches would be more reliable for you. Next time, I would fit a filter before the gauge.

[MY6_Zofia]

So are you saying that your impeller would fail if run dry? So how do you ever prime the system

[boatpoker]

Originally Posted by MY6_Zofia

So are you saying that your impeller would fail if run dry? So how do you ever prime the system

Lube the impeller just like the manufacturer intended with that little tube of lube that came with it ... or use dish soap.

[rslifkin]

Originally Posted by MY6_Zofia

So are you saying that your impeller would fail if run dry? So how do you ever prime the system

More than a few seconds of dry running will cook an impeller. But an impeller and pump housing in good condition will self-prime in a second or so in most cases, long before the impeller self-destructs. And as Boatpoker said, you can help this process further after impeller replacement by lubricating the new impeller.

[SailingHarmonie]

There are several ways this same functionality can be added. If done with care it can be a great addition to the operating system of a generator. Which is best depends on the exact physical setup. Certainly waiting for the freshwater cooling circuit to overheat is not good for any parts of the system. Pump output pressure is certainly one way to monitor this.

Several companies make flow rate switches that can go on the inlet side of the pump that will change state if the flow rate is to low.

You can also put a high temperature switch on the exhaust elbow. This is arguably the best choice because if the exhaust elbow clogs up (which certainly happens) water flow can be reduced without lowering the pressure. It will take a few extra seconds to trip, but in some installations that might be a good thing to reduce nuisance alarms.

[Garrettw]

I have done several things over the years on my Onan MDKBH. At one point I was running an electric AC motor for the raw water and bypassed the belt driven pump. This wasn't 100% reliable though because the generator wouldn't always stabilize the AC output in enough time to get the pump running before the low flow alarm tripped.


For the last 5 years I have something that is kind of verboten in the boat world: a check valve. I have used a check valve to keep a slug of water in the raw water intake line. This has solved all my impeller issues and they last the full maintenance interval and beyond with all vanes intact, every time.

[MY6_Zofia]

Impeller life since Brand new Fischer Price generator
1st 60 hours
2nd 30 hours
3rd 10 hours
4th 6 hours with no air leaks and fully primed strainer before each start.

Genuine parts used each time and lubricant applied

This unit is rubbish

What brand is better. 10 or 15kw

[MY6_Zofia]

Looking for suggestions please members, this Fisher Price toy is driving me nuts. I want to replace it

[boatpoker]

You have a water pump problem, impeller problem or an installer problem.
Nothing to do with the generator.

Hire a mechanic to do the next change and hang over his shoulder.

[MY6_Zofia]

You're correct, so far, touch wood, the generator is working okay. It's the impellers that are not lasting. This is installed in a Fountaine Pajot MY6. They have made over 80 of them so should have the installation correct

[Fuss]

Originally Posted by MY6_Zofia

So are you saying that your impeller would fail if run dry? So how do you ever prime the system

Hmm..I think I have to answer this question ......
- prime the system, do you mean get pressure before the system shuts down......you imagine that it has no pressure so it will never switch on...ok, reasonable thought...so how did it ever switch on when it had no oil pressure? yes, it did switch on, so the same logic applies to the sea water pressure after the pump....as long as you have installed in parallel with the oil pressure shutdown, it will work with the same logic.
I hope that makes sense, its nothing to do with lubing the impeller the first time.

[Captain Bill]

I second the check valve solution. I put one on my genset 12 years ago and haven't replaced an impeller yet due to failure. I did replace the genset in 2018 but I only replaced one impeller in each one as a maintenance item and am stillusing the same line and check valve. My genset raw water pump is over 2 feet above the waterline so this solution works well.

[Cheechako]

Can you refine that down to one sentence?


Boss: "when I ask what time it is, don't tell me how to make a watch!"