Jack and Jill
I wrote yesterday about how, without a lot of effort, I’m growing into a “jack of all trades.” The post was not meant to imply that it was only me going through that transition. On the contrary, Rebecca is right there with me (would that make her a Jill of all trades?). She is very much involved with all of the boat projects, and she has developed a very good eye for when things are not quite right. Take yesterday, for example. After spending a bit of down time at the beach, we returned to the boat and fired up the generator to charge the batteries, and to get a bit of cool air from the AC. After the gen set had been running for a bit, Rebecca popped her head outside and noted that there was no longer any cooling water exiting from the stern. I would hazard a guess that a great many people would not have picked up on that crucial change but she did, earning herself a point on “the list.” *
Putting on my mechanic’s hat, I hypothesized that the lack of cooling water had to do with the impeller in the raw water pump. Since we had a spare, I grabbed my tools and set off to check it out. The water pump on our Northern Lights generator couldn’t be in a more easily accessible spot so within moments, I had it free. Although the impeller seemed to be in reasonably good shape when I took it out, you can see in the photo above that the tines were a little twisted. Even though the old impeller appeared in tact with no missing tines, I replaced it with a new one. Lo and behold, when we fired the generator back up, it started spitting out water again. Woo hoo! And just in time for sundowners too.
Sunday Slackline play time by the beach.
*Rebecca, Michael and I started joking that we are keeping track of “well done” things. No such list actually exists though, or at least I don’t think it does. 🙂
It always amazes me that impellers last as long as they do when you see the distortion that they go through as they rotate. Your picture illustrates it well.
It looks as though that one turned backwards at some stage and didn’t recover properly.
Mike
Yes, and I have no idea how long that impeller has been in there.
I was going to note the same thing that Mike Bruce noted. That impeller appears to be rotating backwards by a few degrees when the engine shuts off. Note that the tines up against the squeegee plate (or whatever it’s called) are pinched backwards instead of laying flat. Also, all of the other tines except for the one at the 5 o-clock position are also bent backwards. It looks like when the engine shut off, residual compression in one of the cylinders caused it to turn backwards just a bit. I would guess that the impeller tends to get creased into that crimped position that you see on the tines in he 2 o-clock to 4 o-clock (squeegee plate) positions.
I don’t know diesel generators all that well, but is it possible that there’s a compression shut-off that’s not doing it’s thing when the engine stops? Maybe a one-way rotation mechanism that’s stuck and allowing the water pump to rotate a fraction backwards during engine shut-off? I wonder if that is normal or expected.
How can you tell from the photo which tines/vanes are facing the proper way? My guess is the opposite of what you are suggesting, and I installed it that way, and it is working.
Sorry about being confusing.
I began with the direction the tines/vanes against the squeegee plate were arranged. I assumed that there isn’t sufficient clearance for the vanes to reverse their direction on the squeegee plate once they’ve pressed against it. Then I saw that in the picture, they aren’t fully extended. I also noted that most of the other vanes are also rotated slightly as-if the impeller had turned clockwise recently. I also noted the final vane in the 5 o-clock position and thought it looked like it might have slid back down the squeegee plate at the same time the other vanes were bent backwards.
I would have expected the the vanes against the squeegee plate would be fully extended if there was no reverse rotation, and that the shaft must normally rotate counter-clockwise, but there are other other possibilities. If the pump reversed itself and then double-reversed itself (bouncing back and forth), you could get the same result.
I might have read it wrong, and it also might not be important anyways. It’s just what I thought when I saw the photo. Based on the position of the vane in the 2 o-clock position, it looks like the assembly rotated backwards by maybe 45-60 degrees (1.5-2 clock positions). Just thinking it through, that kind-of makes sense since there would be 240 degrees rotation between each power stroke on a 3-cylinder diesel and the engine would tend to come to rest midway between one cylinder’s compression stroke and another cylinder’s power stroke – I could see flywheel inertia causing the engine to back up about that much distance to equalize cylinder pressure when it comes to rest if there is no compression cut-off that kicks in when the engine shuts down (not sure about that one).
I don’t intend to identify a problem where there isn’t one. I’m just trying to state what I thought I read in the impeller position. Maybe it’s normal, and it’s just another one of the reasons we need to replace impellers regularly.
I wish the impeller on mt outboard was that easy to access. Gotta love o-rings too because there is no gasket to scrape off and replace.
The reason I asked is threefold.
1. I surmised the opposite of you
2. My friend, who has a similar genset, said he couldn’t tell from the photo
3. I installed the new one the opposite as you indicated and it is now working
I guess that just goes to show how well I can read a photo (not!) 🙂
The important part is that it’s working.
As it turns out Dave, you were correct about the direction. I removed the cover again yesterday to see which way they ended up facing.
You have to love the easy fix that goes as planned 🙂
It balances out the “other ones.”
We have the same style pumps at the nuke plant, to pump morphaline and hydrazine into certain systems. It always amazes me how the vanes can get turned the wrong way! And how often it occurs.
Yes, it would seem to be difficult.
Fortunate for you that it is easily accessible. Ours takes at least a 1/2 day to change because of the location. We try to be proactive and change it regularly, on our terms.
I have been on boats like that!
I’ve had people suggest to me that I should replace the impeller when I change the oil every 100 hours. Good in theory, except my impellers cost more than $35 a piece – when added to 3 gallons of oil and a $30 filter makes for a pricey oil change!
They last a lot longer than that, the current one has been in since I replaced the water pump last November. I suppose I should inspect it more often though, impeller blades would be a nuisance to pick out of the coolers.
Changing the impeller before the vanes break off seems to be the trick.
Oooh, good job Rebecca!
Can I put in a plug for SpeedSeal Impeller covers @ SpeedSeal.com? (Thanks – right up front I’ll tell you there’s no affiliation, they just work really well).
Basically they make the job of getting the cover plate off a MUCH easier job, since they replace the easily damaged philips head screws and thin metal cover plate with 4 thumb screws and a high-quality, thick cover plate.
Cheers!
I didn’t really find it tough getting the plate off. It is held on by six or so 8mm hex head bolts.
Perhaps that may be true for the genset, but how about the engines? Once the SpeedSeal is in place, you only have to remove two screws and loosen the other two. Had to swap out an impeller in rough seas one time and the SpeedSeal made the first and last parts of the job much, much easier. They also make an upgraded cover that is designed to increase the life of the impeller.
I will look at them. They may have to go onto “the list.”
I would go ahead and change the impellers on your engines too– Just so you know where you stand… Impeller wise… You can never have to much raw water coolant!!
It’s on the list. Maybe I need a staff.
When you replace a piece, e.g. an impeller with a spare, do you run out and get a new “spare” or just put it on a list of stuff to have and get it the next time you make a parts run/order?
Well, that depends. In the case of the impeller, or filter, or things of that nature, we purchased a bunch of them. So, at this point, no, I am not running out to buy another one.
Very good catch indeed. Usually, when the water stops, you have 30 seconds before the bad stuff happens. I suppose it depends on the size and speed of impeller.
Perhaps it does.
Mike, that is my job on the boat, and one which Robert sometimes thinks I am too good at…. I find problems/issues and point them out to him! It’s up to him to figure out what’s causing it and/or how to fix it! I’m just the ‘find it’ girl! I find it, you fix it! This has saved us many times, though. I hear things, feel things, etc. before they become a big issue or break!
I’m sure he loves you for it. 🙂
Food for thought. On Ainulindale (and other Lagoon cats, as well) many find that genset impeller replacement is necessary on a far too frequent schedule. This results from a combination of conditions:
1. Be sets can run a higher speeds than other motors.
2. In many installations, the raw water lift hightower ( head) is high.
3. Foot (check) valves installed at the raw water intake are unreliable resulting in loss of prime, further resulting in “dry starts”.
Of course, installations vary and YMMV”.
The point is, we are getting tired of frequently replacing our genset impeller and plan the following “fix” which we found on a Lagoon Owners forum and has apparently resolved the problem quite satisfactorily and with the added benefit of eliminating the impeller, which may be of interest to you and your readers.
We have purchased what is, essentially, a marine, A/C (as opposed to D/C) air conditioning pump, sized for our raw water flow rate, which will be installed at the intake thruhull, along with and after a new intake strainer. It will be wired into the A/C output of the genset so that it is activated at startup. As it is no longer needed, the standard rubber water pump impeller will be permanently removed and the pump left empty but in place. Our older debris strainer which was located up near our genset will be removed as well. I would think that anyone wishing to eliminate hard to reach, or frequent impeller replacements would be interested in exploring this option. As I mentioned, the system is in place one some boats with welcome results.
In the event that you prefer not to pursue the above option, you might want to at least install two items downstream from your existing water pump:
1. A small ss screen strainer which will catch broken bits of impeller vane before they reach and become lodged in your heat exchanger ( remember these should always be recovered any time an impeller is found to be damaged during replacement.
2. A water flow sensor that shuts the genset down anytime loss of flow is detected. This one item has saved our arse many times. It has been so valuable that we keep a spare on board.
Cheers!
Sorry about the typos. Do to the length of my post I had difficulty scrolling up to proof.
Gensets run at higher speeds.
I don’t know where “Hightower” came from.
Damn autocorrect 🙁
🙂
Awesome post!!
MIKE & REBECCA
Just a thought from cruising for awhile.
Due to the nature of cruising we found that some things would slip by us in regards to routine maintenance. Don made up a spread sheet for monthly maintenance. Each day shows something to do to keep up with everything in a timely manner. Example: operating the sea cocks monthly and lubricating. Don has a unique way of doing that while in the water that works beautifully. Then of course there is the list of items not to be forgotten when you are hauled out, like lubricating the thru hulls with Lanocoat. (it is a two person job then) A set o headphone works well for communication while one person inside operates the valve and the outside person sprays the Lanocoat.
The spread sheet could be a temp-let to something you off. Then you would add your own things that are specific to your boat.
We would be glad to share what we have so you don’t have to re invent the “wheel”.
D& Don SV SOUTHERN CROSS
I would love to see a copy of that. Thank you. Our email is:
Zero to cruising ATT gmail DOTT com