Raw water pump impeller sudden failure

[LifesBetterWhenYoureBeating]

A while ago I accidentally ran (for only a few minutes) my Perkins 4.108 with the raw water intake seacock closed, which resulted in a badly damaged impeller in the jabsco water pump">raw water pump connected to it. The engine has been used less than 100h since then, and today when I turned it on there was no water coming out on the exhaust and after checking that there was nothing clogging the intake, I found out that the impeller was completely destroyed. The day before I did run the engine when coming into an anchorage and there was water coming out the exhaust when I turned it on.

Is it normal for impellers to fail suddenly like this, and with so little use?

[sv_pelagia]

Originally Posted by LifesBetterWhenYoureBeating

A while ago I accidentally ran (for only a few minutes) my Perkins 4.108 with the raw water intake seacock closed, which resulted in a badly damaged impeller in the jabsco raw water pump connected to it.

Is it normal for impellers to fail suddenly like this, and with so little use?

Yes, if they are run dry.... but

There are impellers "guaranteed" to be able to run dry for up to 15 minutes:

https://www.globemarinedirect.com/Impellers-s/176.htm

However, these may not have the Yanmar handy threads which make pulling the old impeller so much easier.

There are also pump covers with a rotating disk supposedly saves impeller.

[LifesBetterWhenYoureBeating]

Originally Posted by sv_pelagia

Yes, if they are run dry.... but

I guess if the impeller got slightly damaged it would start sucking less water and possibly lead to more damage until eventually running dry and getting completely destroyed?

[Jolly Roger]

These tiny impellers always struck me as being dangerously inadequate for the serious job they are required to do—feeding the engine with cooling water all the way back to the exhaust outlet, which on my boat is about 25 feet.
Yet I must say, they seem very reliant, and I’ve run my engine more than once by forgetting to open the raw water seacock. I’ve now put a notice next to the starter button. “Check the seacock is open.”
I’ve also fitted a filter after the pump, to catch any bit of an impeller which breaks off, from entering the heat exchanger and blocking it.
Is there nothing more robust than a rubber impeller, to keep raw water flowing?

[wyb2]

I think one of the advantages of a flexible impeller pump is they are fairly tolerant of dirty and minor debris. It needs to be a positive displacement pump so that it will self prime, but I think most positive displacement pumps rely on either tight tolerances or sliding seals. Any little bit of sand or silt will chew through a sliding seal (or open up tight clearances) pretty quickly.

Of course the flexible impeller has a sliding seal, but since it’s integrated into the compressed vanes, the wear is just taken up by the vane expanding slightly.

I would think a possible, maybe even better, alternative would be a diaphragm pump. But that would probably take up quite a bit more physical space.

[Cheechako]

Originally Posted by Jolly Roger

These tiny impellers always struck me as being dangerously inadequate for the serious job they are required to do—feeding the engine with cooling water all the way back to the exhaust outlet, which on my boat is about 25 feet.
Yet I must say, they seem very reliant, and I’ve run my engine more than once by forgetting to open the raw water seacock. I’ve now put a notice next to the starter button. “Check the seacock is open.”
I’ve also fitted a filter after the pump, to catch any bit of an impeller which breaks off, from entering the heat exchanger and blocking it.
Is there nothing more robust than a rubber impeller, to keep raw water flowing?

They dont feed water back to the exhaust outlet. They just pump to the elbow on the back of the engine and exhaust blows it out.

[capt jgw]

Could be the intake got temporarily blocked, plastic bag, jellyfish, etc stuck on the intake. Does the intake have a scoop shaped screen on the outside? It's counter intuitive but those should be installed with the scoop facing AFT, not forward. That way the boat's motion through the water will help slough an obstruction off the screen. Facing forward it's held in place.

[skwanderer]

Originally Posted by Jolly Roger

These tiny impellers always struck me as being dangerously inadequate for the serious job they are required to do—feeding the engine with cooling water all the way back to the exhaust outlet, which on my boat is about 25 feet.
Yet I must say, they seem very reliant, and I’ve run my engine more than once by forgetting to open the raw water seacock. I’ve now put a notice next to the starter button. “Check the seacock is open.”
I’ve also fitted a filter after the pump, to catch any bit of an impeller which breaks off, from entering the heat exchanger and blocking it.
Is there nothing more robust than a rubber impeller, to keep raw water flowing?

Yes!! I greatly appreciated your remark here, as I had my seacocks closed once when I set out, having forgotten to open them. I felt like such an idiot, I'm heartened to hear I'm not alone making this mistake. The result was I saw my engine temp gauge climbing, and considering not trusting my instruments, I ignored it. I finally decided to open the engine hatch and whoosh! Big plumes of steam! Aigh!!! I quickly jumped down and opened the seacocks on the raw water intake when I saw they were still closed, and kept the engines running, thinking this may ensure the now flowing raw water may help cool the engines (that did), and I returned to my silp. The result was the impeller had disintegrated into tiny bits and got lodged in the system, resulting in a costly repair by my diesel mechanic. My point here is that I now use Google Keep notes for a departure checklist for everything, from checking coolant to pfd to vhf on to Seacocks open! You can use the list with checkboxes beside each, and then reset it to untick the boxes and reuse the list. Highly recommend, and I don't have to think if I did everything, I just follow the checklist every time. Screenshot s of my departure checklist attached. Hope this helps someone in the future.

[donradcliffe]

BTDT. Note to self-- open the thru hull valve before the travel lift splashes you. Be sure to take the end cap off the heat exchanger and retrieve all the impeller pieces.

[Madehn]

Clip the key to the seacock valve when you shut down. Simple and idiot proof

[LifesBetterWhenYoureBeating]

Originally Posted by capt jgw

Could be the intake got temporarily blocked, plastic bag, jellyfish, etc stuck on the intake. Does the intake have a scoop shaped screen on the outside? It's counter intuitive but those should be installed with the scoop facing AFT, not forward. That way the boat's motion through the water will help slough an obstruction off the screen. Facing forward it's held in place.

Jellyfish! There were tons of them on that Anchorage. My intake has the scoop facing aft but I guess a big jelly fish could still have blocked it temporarily

[Cwens]

Originally Posted by Jolly Roger

I’ve now put a notice next to the starter button. “Check the seacock is open.”

Whenever you close the seacock, hang the engine start key from the valve handle.

[Jolly Roger]

This is what the impeller looked like after an attempt to drag my boat off a grounding in the intracoastal. It resulted in me having to strip and clean out the whole of the raw water engine system, including two heat exchangers, and the heavy exhaust.
During the repair I installed a filter directly after the pump, which will now capture any bits of impeller or other debris.
The moral is: if you must use your engine to get off a grounding, inspect the impeller directly afterwards. Better still: kedge an anchor and pull her off - more difficult, but a darn-sight easier than stripping a Perkins 4.326, believe me!

[Jolly Roger]

Originally Posted by ChrisOwens

Whenever you close the seacock, hang the engine start key from the valve handle.

That's good advice, except that I don't use a key, and if I did the seacock is 3-feet below the floorboards and the wife just can't reach it. Point taken!

[Searles]

The impeller fitted as a replacement for the damaged one may have been old ,these things do not store well ,fit a new one every year regardless of hrs ,small cost and much safer ,by the way the globe ones are great ,gives you a small edge .⛵️⚓️