Raw water pump impeller wings face wrong way?

[anastas]

Hi all,

I attempted to replace my raw water pump impeller and when I opened the face plate I saw this (see attached photo).
Now, I know for sure that the sea water comes from the bottom right input and leaves to the top left output.
I would expect that this implies that the pump turns clockwise.

Then, why in the world the impeller wings are facing the wrong way (as if the impeller turns counterclockwise)?
Any ideas?

thanks
Achilles

 

[kloudie1]

Sometimes, as the engine is dying, it will come up on a compression stroke that makes it kick backwards a half revolution or so. That is enough to reverse the vanes. Install the new impeller with some grease and before you put the faceplate on, leave the seacock closed, and hit the starter for a second and watch how the vanes behave.

 

[JamesG161]

Look correct to me.

This a flex vane pump.
Jim...

 

[JamesG161]

 

[anastas]

View attachment 214054

He he
Aren't you forgetting that water is an incompressible fluid?

These pumps work with the impeller turning clockwise. That's why I was surprised to see the impeller wings the wrong way. I believe the explanation of @kloudie1 makes sense.

Thank you for your time!

 

[Ralph Johnstone]

The pump is as kosher as matzo ball soup. It turns anti-clockwise if you want the water to go as @JamesG161 shows in post #4.

I would expect that this implies that the pump turns clockwise.

I couldn't imagine that thing turning CW even in my last acid flashback from the 60's.

If I could suggest, first place an arrow on the pump sheave showing the CCW direction of rotation for the impellor. Then lubricate the impellor with hand soap (must be water soluble) and assemble the pump. Replace the pump body and attach the V belt. Kick the engine with the starter and mark an arrow on the crank sheave to show engine rotation :

Follow the direction of rotation down to the pump sheave and see which way the impellor is turning.

 

[anastas]

Hi there,

this short video shows why you are mistaken and the pump should operate clockwise:

in a nutshell, the water circulates the long arc, not the short one from input to output...

anyway thanks for the funny reply!

 

[Ralph Johnstone]

We'll have to forgive you for your mistakes here as the video maker makes a few minor slips with his hands which will confuse the uninitiated.

Notice at 1:23 minutes, the speaker loosely indicates the ingress is on the RH side of the pump and sweeps his hand from right to left. This is incorrect.

At 4:44 - 5:00 the speaker corrects himself and traces the direction of flow from the RH side of the pump off to the heat exchanger mounted on the engine

This will clarify all of your misunderstandings. The impellor turns CCW and the blades are swept backwards.

The flow in this type of pump is always across the short bottom of the casing and NEVER around the long arc.

Carefully notice what the speaker says at 5:40 as to how to bend the impellor blades as they are inserted back into the pump casing.

To finally show you how the impellor blades always bend backwards as they rotate, take your open pump and turn CW for a rotation and then CCW for a rotation. Notice that the blades always flip backwards to trail the direction of rotation.

 

[Davidasailor26]

The speaker in that video is a bit unclear when he puts the impeller back in and suggests water flows over the cam. He probably got tricked when he opened the pump and saw the vane flipped backwards, exactly as @anastas saw. Water does not flow over the cam. @kloudie1 is probably right and the engine rocked back on shutdown.

Here’s how Nigel Calder shows the function of the pump-

The video shows a Yanmar YM series engine just like I have, and I know my impeller spins clockwise, bringing water around the long part of the arc. When I’ve opened my pump the vanes are dragged back in the direction you’d expect, but that’s just luck of the draw with the engine having not rocked backwards.

 

[Terry Cox]

Hi Achilles, the pink color of the bronze pump and flange appears to me in need of a new pump, that is if the photo shows the correct coloring. The pink coloring indicates a serious degradation of the bronze metal due to electrolysis, IMHO. Have a marine technician/mechanic take look see to confirm.

 

[RoyS]

In the video the guy stated to be careful to install the impeller right side up. I never heard this before and I doubt it is true.

 

[anastas]

Thank you for the post @Davidasailor26.
The nice diagram settles this once and for all.

I am summarizing for anyone else who comes across this thread:
These pumps work by transferring water from input to output over the LONG arc.
Sometimes the blades are backwards because when the engine stops it may go backwards half a rotation or so.
Bottom line: nothing to worry about.

Thank you all for your contributions and your time.
Achilles

 

[kloudie1]

Interesting part of Maine Sail's post on impellers:


New Impeller
To install the impeller lube the entire exterior with glycerin. After lubing compress it with your fingers and seat it into the pump body..
I often hear of folks talking of using zip ties to pre-compress the impeller for insertion but I honestly don’t understand why one would need to do so. I’ve replaced impellers on very large Detroit diesels, Cummins, Caterpillars and even one lung teeny tiny Yanmar’s and all of those impellers went back in fine without a zip tie pre-compressing it. You really do not need to over think the re-insertion just do it.
If your impeller had vanes pointing in different directions when you took it out, as the photo of the old one shows, DON’T WORRY. This is rather normal and is due to the little bit of back spin a diesel can develop as it shuts down. Sometimes during the last revolution the engine may actually spin back a notch or two causing the impeller blades to be out of spin direction unison.
Even of you put an impeller in with the vanes completely backwards of the pumps rotation it would correct itself with the first bump of the starter. It is 100% urban myth/dock talk that impeller vanes need to be installed in the direction of rotation.
Pumps just like these, which use identical impellers, are used in industry every single day and the pumps are often forward and reverse pumps switching directions many times per day to drain or fill tanks, vats etc.. Please don’t beat yourself up over vane direction, it simply doesn’t matter..

 

[Ralph Johnstone]

If Calder describes it as going around the long arc, good enough for me. His explanation of WHY it creates flow in the direction it does (and not the opposite) was clear and concise.

The idea of the pump backing up half a turn when stopping never entered into my mind and yet I have seen it many time as I am working on the engine and had someone stop the engine from the helm. And as far as old wive's tales being perpetuated, this is copied right out of the pages of a Yanmar maintenance and operation manual :

The vanes likely flip flop every time the engine stops and backs up half a rev. Label me as having learned something new today and thank you to all who described the flow as over the long arc.

 

[JamesG161]

Looks correct to me.

This a flex vane pump.
Jim...

Now that the smoke has cleared.

No backfire of engine. Broken screws should have told me PO has Zero knowledge about his pump.

Good luck...
Jim...

 

[Davidasailor26]

Now that the smoke has cleared.

View attachment 214079

No backfire of engine. Broken screws should have told me PO has Zero knowledge about his pump.

Good luck...
Jim...

No, vanes just flipped backward as Maine Sail said they sometimes do. The water still flows opposite the arrow you drew. (Or maybe the OP doesn’t know which way the water goes, but I think the phenomenon Maine referenced is more likely.)

Having said that, the broken screws and pink metal aren’t great signs for the life of the pump otherwise.

 

[anastas]

Now that the smoke has cleared.

View attachment 214079

No backfire of engine. Broken screws should have told me PO has Zero knowledge about his pump.

Good luck...
Jim...

Your comments are hilarious:
In your first comment you invented a NEW water pump working by transferring water on the short arc.
In this comment, you have just invented an engine with the raw water going FROM the heat exchanger TO the water inlet valve ;-)

On a general note: I have hit or miss experiences in this forum: there are a few knowledgeable people (eg, in this post @kloudie1, @Davidasailor26, @Terry Cox ) and then there is a number of clueless people with their insistence being inversely proportional to their knowledge and experience.

 

[Ralph Johnstone]

Yes, yes, yes, you're quite right. This discussion did not go well at all from people who should have known far better and I'm no exception. In this case, I attribute my bad remarks to a bad acid flashback from the 60's.

then there is a number of clueless people with their insistence being inversely proportional to their knowledge and experience.

Right again. The number one lesson I've learned and would encourage others to follow is: unless you know 90% of the subject matter of which you are enquiring, do not trust ANY information from on-line forums. Initially knowing 90% first will enable you to determine if what you are looking at is 100% bull.

Search out manufacturer's information first wherever possible.

 

[dlochner]

@Terry Cox noted the color of the bronze is pink. This is a bad sign as it indicates the zinc in the bronze is leaching out. Without zinc the bronze becomes very soft and brittle, likely part of the reason the 2 bolts sheared.

Time to replace the pump before it catastrophically fails at a bad time. Also, check all the other bronze fittings, such as through hulls, struts, and shaft for more pinking.