killing impellers

savanahrae · Post by **savanahrae** » Mon Jul 19, 2010 5:40 pm

I have a Kohler 5E gen set in my Trojan 10 Meter. I have replaced the impeller in the raw water pump twice in the last month and don't know why they are failing. I have attached a picture to show what it looks like when it stops working. When i first replace the impeller it works fine then after several hours it stops pumping water and when I remove the cover plate there is a vane bent in the opposite direction of the others. It always seems to be in the same spot in the pump that the vane is bent backward. I have an idea what is causing it to always flap in the wrong direction at the same point but welcome feedback.

Stripermann2 · Post by **Stripermann2** » Mon Jul 19, 2010 6:00 pm

Can't tell from the pic but Kohler had issues with the housing on some of their models. Is yours plastic? A new housing or pump assembly is bronze I think...

alexander38 · Post by **alexander38** » Mon Jul 19, 2010 7:28 pm

Housing wore out ? Replaced one on port merc 454 did the same thing.

prowlersfish · Post by **prowlersfish** » Mon Jul 19, 2010 7:37 pm

That still should pump OK ,not sucking jelly fish into the pick up are you ? Happen to me several times in the last week , also had to replace intake hoses that were sucking air

k9th · Post by **k9th** » Mon Jul 19, 2010 7:47 pm

I don't believe that I have ever seen an impeller pump housing with an offset like that. The ones I am familiar with are circular with the impeller shaft centered in the housing. I certainly haven't seen them all but am wondering what purpose that would serve except wearing the impeller out quickly.

I work as Chief Engineer of a pump company and while we don't currently make impeller pumps, our competitors do and we have their entire product offering in our engineering lab for evaluation and none of them have an offset housing.

wowzer52 · Post by **wowzer52** » Mon Jul 19, 2010 7:56 pm

That's strange, all the raw water pumps I've seen are like the one pictured.

Big D · Post by **Big D** » Mon Jul 19, 2010 7:58 pm

When the blades pass the offset, they straighten out, increasing the volume between the blades. The process of increasing the volume between two blades creates a vacuum/suction.

wowzer52 · Post by **wowzer52** » Mon Jul 19, 2010 8:07 pm

Here is mine.

Big D · Post by **Big D** » Mon Jul 19, 2010 8:13 pm

As far as I know, all soft impellor pumps work on the same principal of bending the blades then opening them up to create negative pressure.

g36 · Post by **g36** » Mon Jul 19, 2010 8:52 pm

might look into trying a globe impeller. supposed to actually run dry for 15 minutes without damage

http://www.globecomposite.com/pages/products_impeller

Big D · Post by **Big D** » Mon Jul 19, 2010 10:05 pm

If the pump body is plastic and above the water line, I suspect running dry for even 5 minutes will generate enough heat to ruin the body anyway. The trick is not to let them run dry. On a typical Merc Bravo application, the pump is below the water line and in a failure (and normal wear) scores the stainless steel plate even though it's submerged in water.

prowlersfish · Post by **prowlersfish** » Mon Jul 19, 2010 10:29 pm

k9th wrote:I don't believe that I have ever seen an impeller pump housing with an offset like that. The ones I am familiar with are circular with the impeller shaft centered in the housing. I certainly haven't seen them all but am wondering what purpose that would serve except wearing the impeller out quickly.

I work as Chief Engineer of a pump company and while we don't currently make impeller pumps, our competitors do and we have their entire product offering in our engineering lab for evaluation and none of them have an offset housing.

On a impler type pump ,If the housing is circular and the saft is centered then it wont pump very well if at all , there needs to be a offset or partly non-circular shape . some pumps have a insert ( cam)to cause a flat spot in the housing make it not completely circular

Danny Bailey · Post by **Danny Bailey** » Tue Jul 20, 2010 7:28 am

There is nothing in your picture that would keep the pump from working. Most engines roll backward a little when they stop and this will cause what you see in the picture but it is not a problem. Look somewhere else to find why your pump stops pumping.

savanahrae · Post by **savanahrae** » Tue Jul 20, 2010 1:14 pm

Thanks for all the replies. My initial thought was in line with those who suggest a worn out housing. I think the space just past the offset (cam) is worn and when the bent vane is supposed to flex and cause a suction it is losing the vacuum and thereby not drawing water into the pump body. But i am going to check hoses and thru hull before spending the money on a new pump.