Impeller direction 1998 Alpha 1 gen 2 out drive

J

joita

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Sep 20, 2010
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29
Hi,
I am changing my impeller on my Alpha 1 Gen 2 out drive. Does it matter which way the impeller fins are pointing. I would think because it turns clockwise, in forward, the fins should point right to get maximum water flow.

Any insight will be appreciated.impeller.jpg
 

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Bondo

Bondo

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Re: Impeller direction 1998 Alpha 1 gen 2 out drive

Ayuh,... That looks right to me...
 
U

UncleWillie

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Re: Impeller direction 1998 Alpha 1 gen 2 out drive

I believe you may have it in backwards.

AiG2Impeller copy.jpg

The vanes will want to trail the rotation and wipe the walls of the pump. They point Backwards.
If you start the motor the vanes will likely flip the correct way in a short time as soon as they get any friction on the wall of the pump.

These are not inertial (Centrifugal) pumps that pump by spinning the water to the outside of the pump.
Inertial pumps tend to pump from an end to a side.
Your Bilge pump is likely an inertial pump. Water enters from the end of the housing at the center of the pump and exits out of a tube at the side of the pump.

Your cooling water pump is a rotary vane pump.
Rotary Vane pumps tend to pump from one side to the other.
Water enters through a slot on the Bottom Left side. (So to Speak) and exits out a matching slot on the Top Right side.

AiG2IPump.jpg

Look closely and you will notice that the impeller is NOT centered in the pump housing.
The area between the vanes gets smaller and larger as the impeller makes each rotation.
This acts like a 6 chamber (Semi) positive displacement pump.

The rotary Vane pump will produce more pressure than an equivilent inertial pump.
Rotary Vane Pumps requires that the vanes flex on every rotation, so that hard plastic impeller that lasts forever in an inertial pump will not work is this situation.

-------------------------------------

Note: My engineering background prevents me from refering to "Centrifigal Force".
If you believe in the Centrifugal Force, feel free to replace the word "Inertia" with "Centrifugal" wherever you see it. :)

See http://regentsprep.org/regents/physics/phys06/bcentrif/centrif.htm
 
U

UncleWillie

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Oct 18, 2011
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Re: Impeller direction 1998 Alpha 1 gen 2 out drive

Looking closely at your photo again ... :redface:
If the picture is looking "Up" into the pump housing, it will be correct when you flip it over to mount it.
In any event, just look at the "Set" that the rubber in the old impeller has taken, and match it.
 
ktbarrentine

ktbarrentine

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1,296
Re: Impeller direction 1998 Alpha 1 gen 2 out drive

The service manual does a good job of explaining how to get the impeller installed correctly. It warns that if you install it with the vanes pointing the wrong way, damage may result. When replacing mine, the only effective way of even getting the impeller to start into the housing was to lube it up good, and then rotate the drive shaft in the correct direction while installing the pump housing. The impeller will vanes will naturally get their correct bend when this is done. Bottom line, though, you really need to have the service manual pages open to that section while doing the job. Get them on-line and print them out. (lesson learned... I spent good $$ for a hard copy manual before I found the online versions. The nice hard copy version looks good on my workbench, though!)
 
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