Impeller run dry: effect

[mogmog2]

Just in case anyone is interested in what can happen to an impeller that has been run dry for 30 minutes:
New: height 19.26mm, old 19.24-19.35mm
New: diameter 39.56, old 39.56
Lobe width: new 4.5mm old 4.5.
Both spxflow impellers, both new, just one been run for an hour max, of which 30 mins dry.
Vernier caliper is a Mitutoyo 500 series, so not rubbish.
Not what I was expecting.
Discuss.

 

[Bobc]

Doesn't surprise me. People panic too much about stuff like this.

 

[RichardS]

Does not surprise me at all as indicated my many previous posts saying "test your engine out on the hard as not having any cooling water will not do any harm in the short term".

(Of course, it will also depend on when you last lubricated your impeller with silicone grease)

Richard

 

[SlimRick]

Can't tell from a picture whether the rubber has been affected by the heat generated from friction.

 

[VicS]

Just in case anyone is interested in what can happen to an impeller that has been run dry for 30 minutes:
New: height 19.26mm, old 19.24-19.35mm
New: diameter 39.56, old 39.56
Lobe width: new 4.5mm old 4.5.
Both spxflow impellers, both new, just one been run for an hour max, of which 30 mins dry.
Vernier caliper is a Mitutoyo 500 series, so not rubbish.
Not what I was expecting.
Discuss.

It depends on what you mean by this. A big difference , I suspect between running completely dry. with no lubrication when first fitted and allowed to run dry after normal operation with a water flow.

In the former case heat generated may well have affected the impeller and result in an early failure. In the latter case there may well have been sufficient water remaining in the housing to have prevented any serious damage.

 

[mogmog2]

Doesn't surprise me. People panic too much about stuff like this.

Absolutely. That's why posted it. Although I was expecting it to measurably smaller in at least one dimension..

 

[mogmog2]

It depends on what you mean by this. A big difference , I suspect between running completely dry. with no lubrication when first fitted and allowed to run dry after normal operation with a water flow.

In the former case heat generated may well have affected the impeller and result in an early failure. In the latter case there may well have been sufficient water remaining in the housing to have prevented any serious damage.

Im not sure what you mean? I installed it months ago, wiith the glycerine provided. The engine was immediately started a couple of times & a short test drive with the water cock open.
Then some weeks later we motored off & yours truly forgot to open the water cock. It took a full 20 to 30 minutes for the engine to let us know it wasn't happy, by stopping.

I installed the new impeller today but ran out of time to test it to see the Niagara out of the exhaust: previously, a chap at the club commented that it didn't look like enough water was coming out of the exhaust, and I agree (although I have limited experience, it didn't look much) that's partly why I expected to see the impeller in worse shape.

Any idea how much wear on the cover plate is too much? There is a bit of an 'island' in the middle but it's not well defined all the way round.

 

[mogmog2]

Can't tell from a picture whether the rubber has been affected by the heat generated from friction.

It's going in the bin anyway, just expected a bit more measurable wear.

 

[BabySharkDooDooDooDooDoo]

I'm pleasantly surprised that your exhaust isn't knackered by running without any water cooling it

 

[mogmog2]

I'm pleasantly surprised that your exhaust isn't knackered by running without any water cooling it

The hose is alright, but the muffler melted somewhat.

 

[coopec]

I am puzzled as to why OPs are suggesting flexible impeller pumps can be run dry and no damage will be done. Without water or lubrication the rubber impeller would quickly overheat and melt.

But there has been a recent invention
Apr 7, 2015 - This invention relates to a Dry Running Flexible Impeller Pump and Method of Manufacture designed to provide a flexible impeller pump ...

About D.C. Flexible Impeller Pumps / Advice & Support / Xylem ...
https://www.jabscoshop.com/advice.../jabscoshop-about-dc-flexible-impeller-pumps.h...

JABSCO flexible impeller pumps self-prime rapidly from dry, can handle moderate ... Recent Jabsco impeller pump models have built-in dry running protection ...



I will most certainly install my Jabsco in such a way that there always water around the impeller in the pump body

Clive

 

[ghostlymoron]

Conventional wisdom is that a neoprene impeller is rendered useless within minutes. I wouldn't risk any dry running - what's the point.
If you do it accidentally and water still seems to be exiting the exhaust ok, I would still examine the impeller as soon as possible.

 

[mogmog2]

I am puzzled as to why OPs are suggesting flexible impeller pumps can be run dry and no damage will be done. Without water or lubrication the rubber impeller would quickly overheat and melt.

Not sure anyone is suggesting that they can be run dry with no damage?

I experienced no measurable erosion. There is potential for unseen heat damage. Neoprene rubber is good to about 120 degrees C. I've no idea if that temperature is likely. As it didn't melt, I can say it didn't get that hot, despite being run (absolutely) dry for as long as possible!

There is a lot of FUD concerning impellers and I am in that cloud - I was expecting the lobes to have worn noticeably after a prolonged dry run, but they haven't. People have posted fears on here after much less of a dry run so this might at least help make a rational decision if they do.

As a yachtsman, if I was in a foreign port, I'd not fly into a funk and get a new impeller biked in at all costs. I would use the engine as needed to get home and I would order a replacement as soon as practicable. Which I did.

 

[scottie]

The hose is alright, but the muffler melted somewhat.

No delamination of hose you took it off the exhaust Elbow and checked?

 

[PetiteFleur]

Well, that's interesting. Many years ago we were running late and jumped on the boat and started motoring out of the river, forgetting to turn the water on. Within 10 minutes I noticed the engine note change, realised what had happened, leapt below and quickly changed the impellor - which HAD disintegrated, turned on the water and were on our way - just before the tide took us aground... I had fitted knurled thumb screws instead of the silly tiny screws and did have suitable tools & spare impellor immediately in the engine compartment ready to use.
Nowadays, contrary to perceived wisdom, I always leave the engine seacock on...

 

[mogmog2]

Conventional wisdom is that a neoprene impeller is rendered useless within minutes. I wouldn't risk any dry running - what's the point.
If you do it accidentally and water still seems to be exiting the exhaust ok, I would still examine the impeller as soon as possible.

This is my point - "conventional wisdom". I have a hard life as I like to test and challenge conventional/received wisdom & FUD.

How is that impeller "useless"? It has been through impeller Armageddon, not "a few minutes", half an hour- and is still in one piece and is the same physical size, so it will do its job for a while, maybe to get you home. It may be (heat) compromised, but we've both addressed that by agreeing that it should be replaced.

Other people may find theirs resembles 'The Blob', or is in a thousand pieces. Mine isn't. (That's because I use SPXFlow impellers from Johnson. Available from quality marine retailers throughout the country ? )

I'm not advocating keeping it in service, just showing that despite the conventional wisdom saying that it will be a mess, that it's not.

 

[mogmog2]

No delamination of hose you took it off the exhaust Elbow and checked?

No and yes..
I think the bitterly cold March 5am start may have helped? The Vetus swivel muffler elbow melted & let go. At the same time we noticed the smoke (it was dark), the engine stopped...

 

[ghostlymoron]

Each to their own, I've enough to keep me occupied without challenging conventional wisdom.

This is my point - "conventional wisdom". I have a hard life as I like to test and challenge conventional/received wisdom & FUD.

How is that impeller "useless"? It has been through impeller Armageddon, not "a few minutes", half an hour- and is still in one piece and is the same physical size, so it will do its job for a while, maybe to get you home. It may be (heat) compromised, but we've both addressed that by agreeing that it should be replaced.

Other people may find theirs resembles 'The Blob', or is in a thousand pieces. Mine isn't. (That's because I use SPXFlow impellers from Johnson. Available from quality marine retailers throughout the country ? )

I'm not advocating keeping it in service, just showing that despite the conventional wisdom saying that it will be a mess, that it's not.

 

[coopec]

Probably the reason people have got away with running a rubber impeller pump "without water" is that the pump has been installed in such a way there is always water in left in the pump body. Of course that water would eventually boil if the pump was kept running and damage would be inevitable.

Clive

 

[RobbieW]

Last season I must have run the pump dry at some point, I'm guessing early on in the season. I went through 3 impellers before diagnosing that there was some baked on rubber around the body of the pump causing the impeller to fail after about 10 hrs, blades separating from collar. Cleaned that out, which was hard work - no solvent touched it so it was wet'n'dry, and the current impeller has done around 100 hours now (up the Portuguese coast, across Biscay etc when there wasnt enough wind)